[1/6] ASoC: wcd938x: switch to using gpiod API

  From: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Switch the driver from legacy gpio API that is deprecated to the newer
gpiod API that respects line polarities described in ACPI/DT.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
[krzysztof: rebased on recent dev_err_probe() changes]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

---

Cc: Patrick Lai <quic_plai@quicinc.com>
---
 sound/soc/codecs/wcd938x.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)
  

On Thu, Apr 20, 2023 at 12:16:12PM +0200, Krzysztof Kozlowski wrote:

> -	gpio_direction_output(wcd938x->reset_gpio, 0);
> -	/* 20us sleep required after pulling the reset gpio to LOW */
> +	gpiod_set_value_cansleep(wcd938x->reset_gpio, 1);
> +	/* 20us sleep required after asserting the reset gpio */

This is inverting the sense of the GPIO in the API from active low to
active high which will mean we're introducing a new reliance on having
the signal described as active low in DT.  That's an ABI concern.

I remain deeply unconvinced that remapping active low outputs like this
in the GPIO API is helping.
  

On 20/04/2023 13:58, Mark Brown wrote:
> On Thu, Apr 20, 2023 at 12:16:12PM +0200, Krzysztof Kozlowski wrote:
> 
>> -	gpio_direction_output(wcd938x->reset_gpio, 0);
>> -	/* 20us sleep required after pulling the reset gpio to LOW */
>> +	gpiod_set_value_cansleep(wcd938x->reset_gpio, 1);
>> +	/* 20us sleep required after asserting the reset gpio */
> 
> This is inverting the sense of the GPIO in the API from active low to
> active high which will mean we're introducing a new reliance on having
> the signal described as active low in DT.  That's an ABI concern.

It's bringing it to the correct level. Old code was not respecting the
DTS thus if such DTS came with inverted design, the driver would not work.

We were already fixing the upstream DTS users and I thought all of them
are fixed since long time (half a year) or even correct from the
beginning. Now I found one more case with incorrect level, which I will fix.

> 
> I remain deeply unconvinced that remapping active low outputs like this
> in the GPIO API is helping.

The code is mapping them to correct state. The previous state was
incorrect and did not allow to handle active high (which can happen).
This is the effort to make code correct - driver and DTS.

Best regards,
Krzysztof
  

On 20/04/2023 14:30, Krzysztof Kozlowski wrote:
> On 20/04/2023 13:58, Mark Brown wrote:
>> On Thu, Apr 20, 2023 at 12:16:12PM +0200, Krzysztof Kozlowski wrote:
>>
>>> -	gpio_direction_output(wcd938x->reset_gpio, 0);
>>> -	/* 20us sleep required after pulling the reset gpio to LOW */
>>> +	gpiod_set_value_cansleep(wcd938x->reset_gpio, 1);
>>> +	/* 20us sleep required after asserting the reset gpio */
>>
>> This is inverting the sense of the GPIO in the API from active low to
>> active high which will mean we're introducing a new reliance on having
>> the signal described as active low in DT.  That's an ABI concern.
> 
> It's bringing it to the correct level. Old code was not respecting the
> DTS thus if such DTS came with inverted design, the driver would not work.
> 
> We were already fixing the upstream DTS users and I thought all of them
> are fixed since long time (half a year) or even correct from the
> beginning. Now I found one more case with incorrect level, which I will fix.

No, my bad - all upstream DTSes are corrected since half year.

> 
>>
>> I remain deeply unconvinced that remapping active low outputs like this
>> in the GPIO API is helping.
> 
> The code is mapping them to correct state. The previous state was
> incorrect and did not allow to handle active high (which can happen).
> This is the effort to make code correct - driver and DTS.

Best regards,
Krzysztof
  

On Thu, Apr 20, 2023 at 02:30:17PM +0200, Krzysztof Kozlowski wrote:
> On 20/04/2023 13:58, Mark Brown wrote:
> > On Thu, Apr 20, 2023 at 12:16:12PM +0200, Krzysztof Kozlowski wrote:

> >> -	gpio_direction_output(wcd938x->reset_gpio, 0);
> >> -	/* 20us sleep required after pulling the reset gpio to LOW */
> >> +	gpiod_set_value_cansleep(wcd938x->reset_gpio, 1);
> >> +	/* 20us sleep required after asserting the reset gpio */

> > This is inverting the sense of the GPIO in the API from active low to
> > active high which will mean we're introducing a new reliance on having
> > the signal described as active low in DT.  That's an ABI concern.

> It's bringing it to the correct level. Old code was not respecting the
> DTS thus if such DTS came with inverted design, the driver would not work.

Sure, but OTOH if the user didn't bother specifying as active low it
would work.  I suspect it's more likely that someone missed a flag that
had no practical impact in DT than that someone would add an inverter to
their design.

> We were already fixing the upstream DTS users and I thought all of them
> are fixed since long time (half a year) or even correct from the
> beginning. Now I found one more case with incorrect level, which I will fix.

That's just upstream, what about any downstream users?

> > I remain deeply unconvinced that remapping active low outputs like this
> > in the GPIO API is helping.

> The code is mapping them to correct state. The previous state was
> incorrect and did not allow to handle active high (which can happen).
> This is the effort to make code correct - driver and DTS.

We could handle inversions through an explicit property if that were
needed, that would be a less problematic transition and clearer in the
consumer code.
  

On 20/04/2023 15:00, Mark Brown wrote:
> On Thu, Apr 20, 2023 at 02:30:17PM +0200, Krzysztof Kozlowski wrote:
>> On 20/04/2023 13:58, Mark Brown wrote:
>>> On Thu, Apr 20, 2023 at 12:16:12PM +0200, Krzysztof Kozlowski wrote:
> 
>>>> -	gpio_direction_output(wcd938x->reset_gpio, 0);
>>>> -	/* 20us sleep required after pulling the reset gpio to LOW */
>>>> +	gpiod_set_value_cansleep(wcd938x->reset_gpio, 1);
>>>> +	/* 20us sleep required after asserting the reset gpio */
> 
>>> This is inverting the sense of the GPIO in the API from active low to
>>> active high which will mean we're introducing a new reliance on having
>>> the signal described as active low in DT.  That's an ABI concern.
> 
>> It's bringing it to the correct level. Old code was not respecting the
>> DTS thus if such DTS came with inverted design, the driver would not work.
> 
> Sure, but OTOH if the user didn't bother specifying as active low it
> would work.  I suspect it's more likely that someone missed a flag that
> had no practical impact in DT than that someone would add an inverter to
> their design.
> 
>> We were already fixing the upstream DTS users and I thought all of them
>> are fixed since long time (half a year) or even correct from the
>> beginning. Now I found one more case with incorrect level, which I will fix.
> 
> That's just upstream, what about any downstream users?

Life of downstream. We all know the drill: merge your DTS or suffer. The
WCD938x codecs are moderately new, so I do not expect many downstream
users. They are in theory possible, because driver was merged in
v5.14-rc1 and for the newest products Qualcomm uses v5.15. Although now
it is v5.15, but the time driver was merged, maybe it was v5.10.

I could rework this patch to provide backwards compatible solution like
I did for WSA:
https://lore.kernel.org/all/20230102114152.297305-4-krzysztof.kozlowski@linaro.org/

There are downsides of it, but as you pointed out - it's actually very
rare to have the signal inverted in hardware.

> 
>>> I remain deeply unconvinced that remapping active low outputs like this
>>> in the GPIO API is helping.
> 
>> The code is mapping them to correct state. The previous state was
>> incorrect and did not allow to handle active high (which can happen).
>> This is the effort to make code correct - driver and DTS.
> 
> We could handle inversions through an explicit property if that were
> needed, that would be a less problematic transition and clearer in the
> consumer code.

I am not sure if it is worth. The DTS is supposed to describe hardware,
so even if reset pin flag was not effective, it is a mistake to describe
it as ACTIVE_HIGH. Do we care about keeping broken code happy? If yes,
then property is the way to go. If partially, then I can add
backwards-compatible approach like I mentioned above.

Best regards,
Krzysztof
  

On Thu, Apr 20, 2023 at 04:16:59PM +0200, Krzysztof Kozlowski wrote:
> On 20/04/2023 15:00, Mark Brown wrote:

> > That's just upstream, what about any downstream users?

> Life of downstream. We all know the drill: merge your DTS or suffer. The

No, the DT is supposed to be an ABI.  The point in having a domain
specific language with a compiler is to allow device trees to be
distributed independently of the kernel.

> I could rework this patch to provide backwards compatible solution like
> I did for WSA:
> https://lore.kernel.org/all/20230102114152.297305-4-krzysztof.kozlowski@linaro.org/

There we go...

> > We could handle inversions through an explicit property if that were
> > needed, that would be a less problematic transition and clearer in the
> > consumer code.

> I am not sure if it is worth. The DTS is supposed to describe hardware,
> so even if reset pin flag was not effective, it is a mistake to describe
> it as ACTIVE_HIGH. Do we care about keeping broken code happy? If yes,
> then property is the way to go. If partially, then I can add
> backwards-compatible approach like I mentioned above.

It's not just this individual transition, it's the whole thing with
encoding the polarity of the signal at all - it's a layer of abstraction
that feels like it introduces at least as many problems as it solves,
and requiring configuration on every single system integration doesn't
feel like the right choice in general.
  

On 20/04/2023 18:28, Mark Brown wrote:
> On Thu, Apr 20, 2023 at 04:16:59PM +0200, Krzysztof Kozlowski wrote:
>> On 20/04/2023 15:00, Mark Brown wrote:
> 
>>> That's just upstream, what about any downstream users?
> 
>> Life of downstream. We all know the drill: merge your DTS or suffer. The
> 
> No, the DT is supposed to be an ABI.  

No, the DT bindings are the ABI. We are supposed not to break
user-space, but out-of-tree users of drivers are not ABI by itself.
Bindings are. If out-of-tree users make mistakes in their DTS and do not
want to upstream it, it's their choice but it does not come for free.

> The point in having a domain
> specific language with a compiler is to allow device trees to be
> distributed independently of the kernel.

When it is written incorrectly - wrong flag used for GPIO - there is no
requirement to support it.

>> I could rework this patch to provide backwards compatible solution like
>> I did for WSA:
>> https://lore.kernel.org/all/20230102114152.297305-4-krzysztof.kozlowski@linaro.org/
> 
> There we go...
> 
>>> We could handle inversions through an explicit property if that were
>>> needed, that would be a less problematic transition and clearer in the
>>> consumer code.
> 
>> I am not sure if it is worth. The DTS is supposed to describe hardware,
>> so even if reset pin flag was not effective, it is a mistake to describe
>> it as ACTIVE_HIGH. Do we care about keeping broken code happy? If yes,
>> then property is the way to go. If partially, then I can add
>> backwards-compatible approach like I mentioned above.
> 
> It's not just this individual transition, it's the whole thing with
> encoding the polarity of the signal at all - it's a layer of abstraction
> that feels like it introduces at least as many problems as it solves,
> and requiring configuration on every single system integration doesn't
> feel like the right choice in general.

Choosing appropriate flag for GPIO in DTS is not difficult. It was
skipped because we rarely cared in the drivers, but it should have been
chosen correctly. The same about interrupt flags. We had many DTS for
many times marking all possible interrupts as IRQ_TYPE_NONE. Did it
matter for many drivers and setups? No, was perfectly "fine". Is it
correct from DTS point of view. Also no.

Best regards,
Krzysztof
  

On Thu, Apr 20, 2023 at 07:51:27PM +0200, Krzysztof Kozlowski wrote:
> On 20/04/2023 18:28, Mark Brown wrote:
> > On Thu, Apr 20, 2023 at 04:16:59PM +0200, Krzysztof Kozlowski wrote:

> >> Life of downstream. We all know the drill: merge your DTS or suffer. The

> > No, the DT is supposed to be an ABI.  

> No, the DT bindings are the ABI. We are supposed not to break
> user-space, but out-of-tree users of drivers are not ABI by itself.
> Bindings are. If out-of-tree users make mistakes in their DTS and do not
> want to upstream it, it's their choice but it does not come for free.

This is absolutely not the case, users should be able to ship DTs
without upstreaming them and run multiple operating systems on top of a
single DT - ideally boards would ship with DTs in firmware and people
would be able to install generic OSs onto them with just off the shelf
install media.  This is even a thing that people have actually done,
both non-FDT systems like SPARC and the PowerPC systems from Apple and a
few FDT ones like Synquacer.

The enormous costs of DT would hardly be worth it if it were purely an
in tree thing.

> > The point in having a domain
> > specific language with a compiler is to allow device trees to be
> > distributed independently of the kernel.

> When it is written incorrectly - wrong flag used for GPIO - there is no
> requirement to support it.

If it worked was it ever really wrong (and note that the bindings may
not always be super clear...)?  While there is a point at which things
never worked, can be fixed and we don't need to care about it or where
we know the userbase well enough to know there won't be any issue those
shouldn't be the default and should generally be avoided.  Where there
is a good reason to break compatibility it should be something we're
actively deciding to do for a clear reason having considered the
tradeoffs, not something that gets done on a whim without even
mentioning it.

> > It's not just this individual transition, it's the whole thing with
> > encoding the polarity of the signal at all - it's a layer of abstraction
> > that feels like it introduces at least as many problems as it solves,
> > and requiring configuration on every single system integration doesn't
> > feel like the right choice in general.

> Choosing appropriate flag for GPIO in DTS is not difficult. It was
> skipped because we rarely cared in the drivers, but it should have been
> chosen correctly. The same about interrupt flags. We had many DTS for
> many times marking all possible interrupts as IRQ_TYPE_NONE. Did it
> matter for many drivers and setups? No, was perfectly "fine". Is it
> correct from DTS point of view. Also no.

There's no natural definition of "correct" here though - it's just
picking something in a binding.  If someone for example flips the label
on a signal from reset to enable (perhaps during review) that ends up
changing active high to active low, and really I'm not sure how much
we're really winning compared to just having code in the end consumer
which just directly says what value it wants the physical signal to
have.

My point is not that we haven't defined things such that the user has to
specify if something is active high or active low, it's that it feels
like it's more trouble han it's worth.