diff mbox series

[v1] usb: typec: tcpm: Add kernel config to wrap around tcpm logs

Message ID 20230410073134.488762-1-badhri@google.com
State New
Headers
Series [v1] usb: typec: tcpm: Add kernel config to wrap around tcpm logs |

Commit Message

Badhri Jagan Sridharan April 10, 2023, 7:31 a.m. UTC 
  This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
logs to be wrapped around. Additionally, when set, does not clear
the TCPM logs when dumped.

Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
---
 drivers/usb/typec/tcpm/Kconfig | 6 ++++++
 drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

Comments

Greg KH April 10, 2023, 7:45 a.m. UTC | #1 
On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> logs to be wrapped around. Additionally, when set, does not clear
> the TCPM logs when dumped.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> ---
>  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
>  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> index e6b88ca4a4b9..4dd2b594dfc9 100644
> --- a/drivers/usb/typec/tcpm/Kconfig
> +++ b/drivers/usb/typec/tcpm/Kconfig
> @@ -18,6 +18,12 @@ config TYPEC_TCPCI
>  	help
>  	  Type-C Port Controller driver for TCPCI-compliant controller.
>  
> +config TCPM_LOG_WRAPAROUND
> +	bool "Enable TCPM log wraparound"
> +	help
> +	  When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> +	  default gets cleared when dumped and does not wraparound when full.

Kconfig help text needs to be wrapped at the properly width.

And you do not provide any hint here as to why this is not the default
option, or why someone would want this.

So, why is this not just the default operation anyway?  Why would you
ever want the logs cleared?

thanks,

greg k-h
Badhri Jagan Sridharan April 10, 2023, 8:08 a.m. UTC | #2 
On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > logs to be wrapped around. Additionally, when set, does not clear
> > the TCPM logs when dumped.
> >
> > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > ---
> >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> >  2 files changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > --- a/drivers/usb/typec/tcpm/Kconfig
> > +++ b/drivers/usb/typec/tcpm/Kconfig
> > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> >       help
> >         Type-C Port Controller driver for TCPCI-compliant controller.
> >
> > +config TCPM_LOG_WRAPAROUND
> > +     bool "Enable TCPM log wraparound"
> > +     help
> > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > +       default gets cleared when dumped and does not wraparound when full.
>
> Kconfig help text needs to be wrapped at the properly width.

I assumed that the width is 100 characters, but it looks like it is
80. Will fix it in the next version.
>
> And you do not provide any hint here as to why this is not the default
> option, or why someone would want this.

"TCPM logs by default gets cleared when dumped and does not wraparound
when full." was intended
to convey why someone would want to set this. Perhaps it's not effective.

Does the below look better:
"TCPM logs by default gets cleared when dumped and does not wraparound
when full. This can be overridden by setting this config.
When the config is set, TCPM wraps around logs and does not clear the
logs when dumped."

Also, I could make this default if that's OK with Guenter.

>
> So, why is this not just the default operation anyway?  Why would you
> ever want the logs cleared?

I remember Guenter mentioning that he was finding it useful to not
wrap around the logs to fix problems
during tcpm_register_port (init sequence). IMHO wrapping around the
logs helps to triage interoperability
issues uncovered during testing. So both approaches have their own advantages.

Thanks for taking the time to review !
- Badhri

>
> thanks,
>
> greg k-h
Greg KH April 10, 2023, 8:26 a.m. UTC | #3 
On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
> On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > > logs to be wrapped around. Additionally, when set, does not clear
> > > the TCPM logs when dumped.
> > >
> > > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > > ---
> > >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> > >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > > --- a/drivers/usb/typec/tcpm/Kconfig
> > > +++ b/drivers/usb/typec/tcpm/Kconfig
> > > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> > >       help
> > >         Type-C Port Controller driver for TCPCI-compliant controller.
> > >
> > > +config TCPM_LOG_WRAPAROUND
> > > +     bool "Enable TCPM log wraparound"
> > > +     help
> > > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > > +       default gets cleared when dumped and does not wraparound when full.
> >
> > Kconfig help text needs to be wrapped at the properly width.
> 
> I assumed that the width is 100 characters, but it looks like it is
> 80. Will fix it in the next version.
> >
> > And you do not provide any hint here as to why this is not the default
> > option, or why someone would want this.
> 
> "TCPM logs by default gets cleared when dumped and does not wraparound
> when full." was intended
> to convey why someone would want to set this. Perhaps it's not effective.
> 
> Does the below look better:
> "TCPM logs by default gets cleared when dumped and does not wraparound
> when full. This can be overridden by setting this config.
> When the config is set, TCPM wraps around logs and does not clear the
> logs when dumped."
> 
> Also, I could make this default if that's OK with Guenter.
> 
> >
> > So, why is this not just the default operation anyway?  Why would you
> > ever want the logs cleared?
> 
> I remember Guenter mentioning that he was finding it useful to not
> wrap around the logs to fix problems
> during tcpm_register_port (init sequence). IMHO wrapping around the
> logs helps to triage interoperability
> issues uncovered during testing. So both approaches have their own advantages.

But as this is a build-time option, what would cause someone to choose
one over the other, and then when the system is running, they can't
change them?

That does not seem good at all.

Why not just use tracing instead of this odd custom log buffer?  That's
a better solution overall, right?

thanks,

greg k-h
Badhri Jagan Sridharan April 10, 2023, 9 a.m. UTC | #4 
On Mon, Apr 10, 2023 at 1:27 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
> > On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > > > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > > > logs to be wrapped around. Additionally, when set, does not clear
> > > > the TCPM logs when dumped.
> > > >
> > > > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > > > ---
> > > >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> > > >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> > > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > > > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > > > --- a/drivers/usb/typec/tcpm/Kconfig
> > > > +++ b/drivers/usb/typec/tcpm/Kconfig
> > > > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> > > >       help
> > > >         Type-C Port Controller driver for TCPCI-compliant controller.
> > > >
> > > > +config TCPM_LOG_WRAPAROUND
> > > > +     bool "Enable TCPM log wraparound"
> > > > +     help
> > > > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > > > +       default gets cleared when dumped and does not wraparound when full.
> > >
> > > Kconfig help text needs to be wrapped at the properly width.
> >
> > I assumed that the width is 100 characters, but it looks like it is
> > 80. Will fix it in the next version.
> > >
> > > And you do not provide any hint here as to why this is not the default
> > > option, or why someone would want this.
> >
> > "TCPM logs by default gets cleared when dumped and does not wraparound
> > when full." was intended
> > to convey why someone would want to set this. Perhaps it's not effective.
> >
> > Does the below look better:
> > "TCPM logs by default gets cleared when dumped and does not wraparound
> > when full. This can be overridden by setting this config.
> > When the config is set, TCPM wraps around logs and does not clear the
> > logs when dumped."
> >
> > Also, I could make this default if that's OK with Guenter.
> >
> > >
> > > So, why is this not just the default operation anyway?  Why would you
> > > ever want the logs cleared?
> >
> > I remember Guenter mentioning that he was finding it useful to not
> > wrap around the logs to fix problems
> > during tcpm_register_port (init sequence). IMHO wrapping around the
> > logs helps to triage interoperability
> > issues uncovered during testing. So both approaches have their own advantages.
>
> But as this is a build-time option, what would cause someone to choose
> one over the other, and then when the system is running, they can't
> change them?

During initial phases of bringup, it makes sense to not wrap around
the logs, but, once bringup is done its most effective to wraparound
so that interop issues reported by the end users can be triaged where
TCPM logs are very effective.
Also, without wrapping around, the logbuffer logs are completely stale
after the user goes through a few USB connect and disconnect cycles
till the system is rebooted.
If we don't want to pursue the Kconfig option, we should atleast make
TCPM default to wrapping the logs around when full so we could
maximise the use of the logbuffer contents.

>
> That does not seem good at all.
>
> Why not just use tracing instead of this odd custom log buffer?  That's
> a better solution overall, right?

Tracing is not enabled by default in most systems. End users don't
want to retry and reproduce the failure to collect traces even if they
could reproduce it consistently.
So tracing was not proving handy here.

Thanks,
Badhri

>
> thanks,
>
> greg k-h
Badhri Jagan Sridharan April 10, 2023, 9:08 a.m. UTC | #5 
On Mon, Apr 10, 2023 at 2:00 AM Badhri Jagan Sridharan
<badhri@google.com> wrote:
>
> On Mon, Apr 10, 2023 at 1:27 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
> > > On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > > > > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > > > > logs to be wrapped around. Additionally, when set, does not clear
> > > > > the TCPM logs when dumped.
> > > > >
> > > > > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > > > > ---
> > > > >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> > > > >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> > > > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > > > > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > > > > --- a/drivers/usb/typec/tcpm/Kconfig
> > > > > +++ b/drivers/usb/typec/tcpm/Kconfig
> > > > > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> > > > >       help
> > > > >         Type-C Port Controller driver for TCPCI-compliant controller.
> > > > >
> > > > > +config TCPM_LOG_WRAPAROUND
> > > > > +     bool "Enable TCPM log wraparound"
> > > > > +     help
> > > > > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > > > > +       default gets cleared when dumped and does not wraparound when full.
> > > >
> > > > Kconfig help text needs to be wrapped at the properly width.
> > >
> > > I assumed that the width is 100 characters, but it looks like it is
> > > 80. Will fix it in the next version.
> > > >
> > > > And you do not provide any hint here as to why this is not the default
> > > > option, or why someone would want this.
> > >
> > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > when full." was intended
> > > to convey why someone would want to set this. Perhaps it's not effective.
> > >
> > > Does the below look better:
> > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > when full. This can be overridden by setting this config.
> > > When the config is set, TCPM wraps around logs and does not clear the
> > > logs when dumped."
> > >
> > > Also, I could make this default if that's OK with Guenter.
> > >
> > > >
> > > > So, why is this not just the default operation anyway?  Why would you
> > > > ever want the logs cleared?
> > >
> > > I remember Guenter mentioning that he was finding it useful to not
> > > wrap around the logs to fix problems
> > > during tcpm_register_port (init sequence). IMHO wrapping around the
> > > logs helps to triage interoperability
> > > issues uncovered during testing. So both approaches have their own advantages.
> >
> > But as this is a build-time option, what would cause someone to choose
> > one over the other, and then when the system is running, they can't
> > change them?
>
> During initial phases of bringup, it makes sense to not wrap around
> the logs, but, once bringup is done its most effective to wraparound
> so that interop issues reported by the end users can be triaged where
> TCPM logs are very effective.
> Also, without wrapping around, the logbuffer logs are completely stale
> after the user goes through a few USB connect and disconnect cycles
> till the system is rebooted.
> If we don't want to pursue the Kconfig option, we should atleast make
> TCPM default to wrapping the logs around when full so we could
> maximise the use of the logbuffer contents.
>

The other option that I could think of is to expose another debugfs node
that can be used to control wrapping around the logs in runtime.

Thanks,
Badhri

> >
> > That does not seem good at all.
> >
> > Why not just use tracing instead of this odd custom log buffer?  That's
> > a better solution overall, right?
>
> Tracing is not enabled by default in most systems. End users don't
> want to retry and reproduce the failure to collect traces even if they
> could reproduce it consistently.
> So tracing was not proving handy here.
>
> Thanks,
> Badhri
>
> >
> > thanks,
> >
> > greg k-h
Guenter Roeck April 10, 2023, 2:13 p.m. UTC | #6 
On 4/10/23 01:08, Badhri Jagan Sridharan wrote:
> On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>>
>> On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
>>> This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
>>> logs to be wrapped around. Additionally, when set, does not clear
>>> the TCPM logs when dumped.
>>>
>>> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
>>> ---
>>>   drivers/usb/typec/tcpm/Kconfig | 6 ++++++
>>>   drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
>>>   2 files changed, 13 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
>>> index e6b88ca4a4b9..4dd2b594dfc9 100644
>>> --- a/drivers/usb/typec/tcpm/Kconfig
>>> +++ b/drivers/usb/typec/tcpm/Kconfig
>>> @@ -18,6 +18,12 @@ config TYPEC_TCPCI
>>>        help
>>>          Type-C Port Controller driver for TCPCI-compliant controller.
>>>
>>> +config TCPM_LOG_WRAPAROUND
>>> +     bool "Enable TCPM log wraparound"
>>> +     help
>>> +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
>>> +       default gets cleared when dumped and does not wraparound when full.
>>
>> Kconfig help text needs to be wrapped at the properly width.
> 
> I assumed that the width is 100 characters, but it looks like it is
> 80. Will fix it in the next version.
>>
>> And you do not provide any hint here as to why this is not the default
>> option, or why someone would want this.
> 
> "TCPM logs by default gets cleared when dumped and does not wraparound
> when full." was intended
> to convey why someone would want to set this. Perhaps it's not effective.
> 
> Does the below look better:
> "TCPM logs by default gets cleared when dumped and does not wraparound
> when full. This can be overridden by setting this config.
> When the config is set, TCPM wraps around logs and does not clear the
> logs when dumped."
> 
> Also, I could make this default if that's OK with Guenter.
> 

The reason to not wrap around the buffer was that it tends to fill up quickly
if something goes wrong. Initially I had it wrap around and often ended up
seeing endless reset sequences in the log but not the actual problem.

>>
>> So, why is this not just the default operation anyway?  Why would you
>> ever want the logs cleared?
> 
> I remember Guenter mentioning that he was finding it useful to not
> wrap around the logs to fix problems
> during tcpm_register_port (init sequence). IMHO wrapping around the
> logs helps to triage interoperability
> issues uncovered during testing. So both approaches have their own advantages.
> 
Yes, except that "testing" at the time included connecting an arbitrary new
device to the type c port. Pretty much each of them had its own flaws.
This was also the reason for not using tracing, because I wanted to have a
log available _all_ the time, not just when explicitly enabled.

Maybe the protocol is now more stable than it used to be, and switching
to a wraparound buffer and/or to tracing makes more sense now.
I can't really say.

Guenter

> Thanks for taking the time to review !
> - Badhri
> 
>>
>> thanks,
>>
>> greg k-h
Guenter Roeck April 10, 2023, 5 p.m. UTC | #7 
On Mon, Apr 10, 2023 at 02:00:08AM -0700, Badhri Jagan Sridharan wrote:
> On Mon, Apr 10, 2023 at 1:27 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
> > > On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > > > > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > > > > logs to be wrapped around. Additionally, when set, does not clear
> > > > > the TCPM logs when dumped.
> > > > >
> > > > > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > > > > ---
> > > > >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> > > > >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> > > > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > > > > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > > > > --- a/drivers/usb/typec/tcpm/Kconfig
> > > > > +++ b/drivers/usb/typec/tcpm/Kconfig
> > > > > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> > > > >       help
> > > > >         Type-C Port Controller driver for TCPCI-compliant controller.
> > > > >
> > > > > +config TCPM_LOG_WRAPAROUND
> > > > > +     bool "Enable TCPM log wraparound"
> > > > > +     help
> > > > > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > > > > +       default gets cleared when dumped and does not wraparound when full.
> > > >
> > > > Kconfig help text needs to be wrapped at the properly width.
> > >
> > > I assumed that the width is 100 characters, but it looks like it is
> > > 80. Will fix it in the next version.
> > > >
> > > > And you do not provide any hint here as to why this is not the default
> > > > option, or why someone would want this.
> > >
> > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > when full." was intended
> > > to convey why someone would want to set this. Perhaps it's not effective.
> > >
> > > Does the below look better:
> > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > when full. This can be overridden by setting this config.
> > > When the config is set, TCPM wraps around logs and does not clear the
> > > logs when dumped."
> > >
> > > Also, I could make this default if that's OK with Guenter.
> > >
> > > >
> > > > So, why is this not just the default operation anyway?  Why would you
> > > > ever want the logs cleared?
> > >
> > > I remember Guenter mentioning that he was finding it useful to not
> > > wrap around the logs to fix problems
> > > during tcpm_register_port (init sequence). IMHO wrapping around the
> > > logs helps to triage interoperability
> > > issues uncovered during testing. So both approaches have their own advantages.
> >
> > But as this is a build-time option, what would cause someone to choose
> > one over the other, and then when the system is running, they can't
> > change them?
> 
> During initial phases of bringup, it makes sense to not wrap around
> the logs, but, once bringup is done its most effective to wraparound
> so that interop issues reported by the end users can be triaged where
> TCPM logs are very effective.

Not really, because the problem tends to be the remote device
(or at least it used to be), not a driver under development.

> Also, without wrapping around, the logbuffer logs are completely stale
> after the user goes through a few USB connect and disconnect cycles
> till the system is rebooted.

Unless they are cleared.

Again, the premise is wrong here. The idea was to ensure that the
beginning of a problem is caught and available in the log, not its tail.
This includes "beginning" as the behavior immediately after boot regarding
an already connected device, and the behavior observed when inserting
a device into the running system. Again, in both cases it was most
important to catch the beginning of a problem, not its tail.

> If we don't want to pursue the Kconfig option, we should atleast make
> TCPM default to wrapping the logs around when full so we could
> maximise the use of the logbuffer contents.
> 

I don't really agree, but then I am not in a position to argue either.
Maybe the premise and reasons have changed since I wrote the driver.

Guenter

> >
> > That does not seem good at all.
> >
> > Why not just use tracing instead of this odd custom log buffer?  That's
> > a better solution overall, right?
> 
> Tracing is not enabled by default in most systems. End users don't
> want to retry and reproduce the failure to collect traces even if they
> could reproduce it consistently.
> So tracing was not proving handy here.
> 
> Thanks,
> Badhri
> 
> >
> > thanks,
> >
> > greg k-h
Badhri Jagan Sridharan April 10, 2023, 8:57 p.m. UTC | #8 
On Mon, Apr 10, 2023 at 10:00 AM Guenter Roeck <linux@roeck-us.net> wrote:
>
> On Mon, Apr 10, 2023 at 02:00:08AM -0700, Badhri Jagan Sridharan wrote:
> > On Mon, Apr 10, 2023 at 1:27 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
> > > > On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > > >
> > > > > On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
> > > > > > This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
> > > > > > logs to be wrapped around. Additionally, when set, does not clear
> > > > > > the TCPM logs when dumped.
> > > > > >
> > > > > > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > > > > > ---
> > > > > >  drivers/usb/typec/tcpm/Kconfig | 6 ++++++
> > > > > >  drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
> > > > > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
> > > > > > index e6b88ca4a4b9..4dd2b594dfc9 100644
> > > > > > --- a/drivers/usb/typec/tcpm/Kconfig
> > > > > > +++ b/drivers/usb/typec/tcpm/Kconfig
> > > > > > @@ -18,6 +18,12 @@ config TYPEC_TCPCI
> > > > > >       help
> > > > > >         Type-C Port Controller driver for TCPCI-compliant controller.
> > > > > >
> > > > > > +config TCPM_LOG_WRAPAROUND
> > > > > > +     bool "Enable TCPM log wraparound"
> > > > > > +     help
> > > > > > +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
> > > > > > +       default gets cleared when dumped and does not wraparound when full.
> > > > >
> > > > > Kconfig help text needs to be wrapped at the properly width.
> > > >
> > > > I assumed that the width is 100 characters, but it looks like it is
> > > > 80. Will fix it in the next version.
> > > > >
> > > > > And you do not provide any hint here as to why this is not the default
> > > > > option, or why someone would want this.
> > > >
> > > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > > when full." was intended
> > > > to convey why someone would want to set this. Perhaps it's not effective.
> > > >
> > > > Does the below look better:
> > > > "TCPM logs by default gets cleared when dumped and does not wraparound
> > > > when full. This can be overridden by setting this config.
> > > > When the config is set, TCPM wraps around logs and does not clear the
> > > > logs when dumped."
> > > >
> > > > Also, I could make this default if that's OK with Guenter.
> > > >
> > > > >
> > > > > So, why is this not just the default operation anyway?  Why would you
> > > > > ever want the logs cleared?
> > > >
> > > > I remember Guenter mentioning that he was finding it useful to not
> > > > wrap around the logs to fix problems
> > > > during tcpm_register_port (init sequence). IMHO wrapping around the
> > > > logs helps to triage interoperability
> > > > issues uncovered during testing. So both approaches have their own advantages.
> > >
> > > But as this is a build-time option, what would cause someone to choose
> > > one over the other, and then when the system is running, they can't
> > > change them?
> >
> > During initial phases of bringup, it makes sense to not wrap around
> > the logs, but, once bringup is done its most effective to wraparound
> > so that interop issues reported by the end users can be triaged where
> > TCPM logs are very effective.
>
> Not really, because the problem tends to be the remote device
> (or at least it used to be), not a driver under development.

Thanks for clarifying Guenter !
Right now if we DONT wrap around, once an issue is observed with a
remote device, the logs have to be cleared(if already full) and then
the issue has to be reproduced to collect the TCPM logbuffer
logsagain.

Having a log available _all_ the time, not just when explicitly
enabled is still very useful to catch hard to reproduce intertop
issues.

Given this would you be OK if I change the logic to wrap around always ?

IMHO based on what I have seen in the last couple of years, this would
also cover the boot with accessory connected as if the link gets into
a reset loop, the sequence after the reset reveals what had gone
wrong.

>
> > Also, without wrapping around, the logbuffer logs are completely stale
> > after the user goes through a few USB connect and disconnect cycles
> > till the system is rebooted.
>
> Unless they are cleared.

Ah yes. I forgot about that. Wrapping around would still make TCPM
logbuffer logs  more effective to debug issues with remote device.

Thanks,
Badhri





>
> Again, the premise is wrong here. The idea was to ensure that the
> beginning of a problem is caught and available in the log, not its tail.
> This includes "beginning" as the behavior immediately after boot regarding
> an already connected device, and the behavior observed when inserting
> a device into the running system. Again, in both cases it was most
> important to catch the beginning of a problem, not its tail.
>
> > If we don't want to pursue the Kconfig option, we should atleast make
> > TCPM default to wrapping the logs around when full so we could
> > maximise the use of the logbuffer contents.
> >
>
> I don't really agree, but then I am not in a position to argue either.
> Maybe the premise and reasons have changed since I wrote the driver.
>
> Guenter
>
> > >
> > > That does not seem good at all.
> > >
> > > Why not just use tracing instead of this odd custom log buffer?  That's
> > > a better solution overall, right?
> >
> > Tracing is not enabled by default in most systems. End users don't
> > want to retry and reproduce the failure to collect traces even if they
> > could reproduce it consistently.
> > So tracing was not proving handy here.
> >
> > Thanks,
> > Badhri
> >
> > >
> > > thanks,
> > >
> > > greg k-h
Guenter Roeck April 10, 2023, 10:12 p.m. UTC | #9 
On 4/10/23 13:57, Badhri Jagan Sridharan wrote:
> On Mon, Apr 10, 2023 at 10:00 AM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> On Mon, Apr 10, 2023 at 02:00:08AM -0700, Badhri Jagan Sridharan wrote:
>>> On Mon, Apr 10, 2023 at 1:27 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>>>>
>>>> On Mon, Apr 10, 2023 at 01:08:55AM -0700, Badhri Jagan Sridharan wrote:
>>>>> On Mon, Apr 10, 2023 at 12:45 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>>>>>>
>>>>>> On Mon, Apr 10, 2023 at 07:31:34AM +0000, Badhri Jagan Sridharan wrote:
>>>>>>> This change adds CONFIG_TCPM_LOG_WRAPAROUND which when set allows the
>>>>>>> logs to be wrapped around. Additionally, when set, does not clear
>>>>>>> the TCPM logs when dumped.
>>>>>>>
>>>>>>> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
>>>>>>> ---
>>>>>>>   drivers/usb/typec/tcpm/Kconfig | 6 ++++++
>>>>>>>   drivers/usb/typec/tcpm/tcpm.c  | 9 +++++++--
>>>>>>>   2 files changed, 13 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
>>>>>>> index e6b88ca4a4b9..4dd2b594dfc9 100644
>>>>>>> --- a/drivers/usb/typec/tcpm/Kconfig
>>>>>>> +++ b/drivers/usb/typec/tcpm/Kconfig
>>>>>>> @@ -18,6 +18,12 @@ config TYPEC_TCPCI
>>>>>>>        help
>>>>>>>          Type-C Port Controller driver for TCPCI-compliant controller.
>>>>>>>
>>>>>>> +config TCPM_LOG_WRAPAROUND
>>>>>>> +     bool "Enable TCPM log wraparound"
>>>>>>> +     help
>>>>>>> +       When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
>>>>>>> +       default gets cleared when dumped and does not wraparound when full.
>>>>>>
>>>>>> Kconfig help text needs to be wrapped at the properly width.
>>>>>
>>>>> I assumed that the width is 100 characters, but it looks like it is
>>>>> 80. Will fix it in the next version.
>>>>>>
>>>>>> And you do not provide any hint here as to why this is not the default
>>>>>> option, or why someone would want this.
>>>>>
>>>>> "TCPM logs by default gets cleared when dumped and does not wraparound
>>>>> when full." was intended
>>>>> to convey why someone would want to set this. Perhaps it's not effective.
>>>>>
>>>>> Does the below look better:
>>>>> "TCPM logs by default gets cleared when dumped and does not wraparound
>>>>> when full. This can be overridden by setting this config.
>>>>> When the config is set, TCPM wraps around logs and does not clear the
>>>>> logs when dumped."
>>>>>
>>>>> Also, I could make this default if that's OK with Guenter.
>>>>>
>>>>>>
>>>>>> So, why is this not just the default operation anyway?  Why would you
>>>>>> ever want the logs cleared?
>>>>>
>>>>> I remember Guenter mentioning that he was finding it useful to not
>>>>> wrap around the logs to fix problems
>>>>> during tcpm_register_port (init sequence). IMHO wrapping around the
>>>>> logs helps to triage interoperability
>>>>> issues uncovered during testing. So both approaches have their own advantages.
>>>>
>>>> But as this is a build-time option, what would cause someone to choose
>>>> one over the other, and then when the system is running, they can't
>>>> change them?
>>>
>>> During initial phases of bringup, it makes sense to not wrap around
>>> the logs, but, once bringup is done its most effective to wraparound
>>> so that interop issues reported by the end users can be triaged where
>>> TCPM logs are very effective.
>>
>> Not really, because the problem tends to be the remote device
>> (or at least it used to be), not a driver under development.
> 
> Thanks for clarifying Guenter !
> Right now if we DONT wrap around, once an issue is observed with a
> remote device, the logs have to be cleared(if already full) and then
> the issue has to be reproduced to collect the TCPM logbuffer
> logsagain.
> 
> Having a log available _all_ the time, not just when explicitly
> enabled is still very useful to catch hard to reproduce intertop
> issues.
> 
> Given this would you be OK if I change the logic to wrap around always ?
> 
> IMHO based on what I have seen in the last couple of years, this would
> also cover the boot with accessory connected as if the link gets into
> a reset loop, the sequence after the reset reveals what had gone
> wrong.
> 

I have no strong opinion. As I said, maybe conditions have changed.
When I wrote the code, failure conditions happened all the time, and
reset loops overwrote the log repeatedly. I didn't implement the current
code because I was lazy or something, it was because wrap-around
did not work for me. Again, maybe the situation has changed.
And, to follow-up on Greg's question, maybe switching to tracing
instead of re-implementing it would make sense nowadays. I simply
don't know. I'll accept whatever solution you and Greg can agree on.

Thanks,
Guenter
diff mbox series

Patch

diff --git a/drivers/usb/typec/tcpm/Kconfig b/drivers/usb/typec/tcpm/Kconfig
index e6b88ca4a4b9..4dd2b594dfc9 100644
--- a/drivers/usb/typec/tcpm/Kconfig
+++ b/drivers/usb/typec/tcpm/Kconfig
@@ -18,6 +18,12 @@  config TYPEC_TCPCI
 	help
 	  Type-C Port Controller driver for TCPCI-compliant controller.
 
+config TCPM_LOG_WRAPAROUND
+	bool "Enable TCPM log wraparound"
+	help
+	  When set, wraps around TCPM logs and does not clear the logs when dumped. TCPM logs by
+	  default gets cleared when dumped and does not wraparound when full.
+
 if TYPEC_TCPCI
 
 config TYPEC_RT1711H
diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index ab3a54662ed9..3f708749431b 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -619,7 +619,7 @@  static void _tcpm_log(struct tcpm_port *port, const char *fmt, va_list args)
 
 	vsnprintf(tmpbuffer, sizeof(tmpbuffer), fmt, args);
 
-	if (tcpm_log_full(port)) {
+	if (!IS_ENABLED(CONFIG_TCPM_LOG_WRAPAROUND) && tcpm_log_full(port)) {
 		port->logbuffer_head = max(port->logbuffer_head - 1, 0);
 		strcpy(tmpbuffer, "overflow");
 	}
@@ -644,6 +644,10 @@  static void _tcpm_log(struct tcpm_port *port, const char *fmt, va_list args)
 		  tmpbuffer);
 	port->logbuffer_head = (port->logbuffer_head + 1) % LOG_BUFFER_ENTRIES;
 
+	if (IS_ENABLED(CONFIG_TCPM_LOG_WRAPAROUND) && port->logbuffer_head == port->logbuffer_tail)
+		port->logbuffer_tail =
+			(port->logbuffer_tail + 1) % LOG_BUFFER_ENTRIES;
+
 abort:
 	mutex_unlock(&port->logbuffer_lock);
 }
@@ -746,7 +750,8 @@  static int tcpm_debug_show(struct seq_file *s, void *v)
 		seq_printf(s, "%s\n", port->logbuffer[tail]);
 		tail = (tail + 1) % LOG_BUFFER_ENTRIES;
 	}
-	if (!seq_has_overflowed(s))
+
+	if (!IS_ENABLED(CONFIG_TCPM_LOG_WRAPAROUND) && !seq_has_overflowed(s))
 		port->logbuffer_tail = tail;
 	mutex_unlock(&port->logbuffer_lock);