diff mbox series

i40e: fix the wrong PTP frequency calculation

Message ID 20230627022658.1876747-1-yajun.deng@linux.dev
State New
Headers
Series i40e: fix the wrong PTP frequency calculation |

Commit Message

Yajun Deng June 27, 2023, 2:26 a.m. UTC 
  The new adjustment should be based on the base frequency, not the
I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().

This issue was introduced in commit 3626a690b717 ("i40e: use
mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
parts per million"). However the latter is a new feature and hasn't been
backported to the stable releases.

This issue affects both v6.0 and v6.1 versions, and the v6.1 version is
an LTS version.

Fixes: 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for PTP frequency calculation")
Cc: <stable@vger.kernel.org> # 6.1
Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
 drivers/net/ethernet/intel/i40e/i40e_ptp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Jacob Keller June 27, 2023, 8:20 p.m. UTC | #1 
On 6/26/2023 7:26 PM, Yajun Deng wrote:
> The new adjustment should be based on the base frequency, not the
> I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().
> 
> This issue was introduced in commit 3626a690b717 ("i40e: use
> mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
> commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
> parts per million"). However the latter is a new feature and hasn't been
> backported to the stable releases.
> 
> This issue affects both v6.0 and v6.1 versions, and the v6.1 version is
> an LTS version.
> 
> Fixes: 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for PTP frequency calculation")
> Cc: <stable@vger.kernel.org> # 6.1
> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_ptp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_ptp.c b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
> index ffea0c9c82f1..97a9efe7b713 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_ptp.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
> @@ -361,9 +361,9 @@ static int i40e_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
>  				   1000000ULL << 16);
>  
>  	if (neg_adj)
> -		adj = I40E_PTP_40GB_INCVAL - diff;
> +		adj = freq - diff;
>  	else
> -		adj = I40E_PTP_40GB_INCVAL + diff;
> +		adj = freq + diff;
>  
>  	wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>  	wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);

This straight forward fix makes sense. However, it wasn't obvious to me
without context why the 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for
PTP frequency calculation") was where the fault got introduced. Thus,
here is that context for anyone else who failed to spot it just looking
at shrunk patch diffs.

--> code before that commit <---
> /**
>  * i40e_ptp_adjfreq - Adjust the PHC frequency
>  * @ptp: The PTP clock structure
>  * @ppb: Parts per billion adjustment from the base
>  *
>  * Adjust the frequency of the PHC by the indicated parts per billion from the
>  * base frequency.
>  **/
> static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
> {
>         struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>         struct i40e_hw *hw = &pf->hw;
>         u64 adj, freq, diff;
>         int neg_adj = 0;
> 
>         if (ppb < 0) {
>                 neg_adj = 1;
>                 ppb = -ppb;
>         }
> 
>         freq = I40E_PTP_40GB_INCVAL;

frequency is left just as base I40E_PTP_40GB_INCVAL.

>         freq *= ppb;
>         diff = div_u64(freq, 1000000000ULL);
> 
>         if (neg_adj)
>                 adj = I40E_PTP_40GB_INCVAL - diff;
>         else
>                 adj = I40E_PTP_40GB_INCVAL + diff;
> 

So the base here can't be freq since we modify freq above using *=, but
using I40E_PTP_40GB_INCVAL is consistent.

>         /* At some link speeds, the base incval is so large that directly
>          * multiplying by ppb would result in arithmetic overflow even when
>          * using a u64. Avoid this by instead calculating the new incval
>          * always in terms of the 40GbE clock rate and then multiplying by the
>          * link speed factor afterwards. This does result in slightly lower
>          * precision at lower link speeds, but it is fairly minor.
>          */
>         smp_mb(); /* Force any pending update before accessing. */
>         adj *= READ_ONCE(pf->ptp_adj_mult);
> 

Finally, the multiply is applied last. This affects the combined base +
difference, and is done in order to avoid overflowing the *= used in the
original implementation.

>         wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>         wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
> 
>         return 0;
> }


---> code after that commit <---
> /**
>  * i40e_ptp_adjfreq - Adjust the PHC frequency
>  * @ptp: The PTP clock structure
>  * @ppb: Parts per billion adjustment from the base
>  *
>  * Adjust the frequency of the PHC by the indicated parts per billion from the
>  * base frequency.
>  **/
> static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
> {
>         struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>         struct i40e_hw *hw = &pf->hw;
>         u64 adj, freq, diff;
>         int neg_adj = 0;
> 
>         if (ppb < 0) {
>                 neg_adj = 1;
>                 ppb = -ppb;
>         }
> 
>         smp_mb(); /* Force any pending update before accessing. */
>         freq = I40E_PTP_40GB_INCVAL * READ_ONCE(pf->ptp_adj_mult);
>         diff = mul_u64_u64_div_u64(freq, (u64)ppb,
>                                    1000000000ULL);
> 

Here, we assign freq to be the I40E_PTP_40GB_INCVAL times the
ptp_adj_mult value, and then we don't modify it, instead using
mul_u64_u64_div_u64.

>         if (neg_adj)
>                 adj = I40E_PTP_40GB_INCVAL - diff;
>         else
>                 adj = I40E_PTP_40GB_INCVAL + diff;
> 

But then the diff is applied on the wrong value, and no multiplication
is done afterwards.

>         wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>         wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
> 
>         return 0;
> }

---> current version with adjust_by_scaled_ppm <---
> /**
>  * i40e_ptp_adjfine - Adjust the PHC frequency
>  * @ptp: The PTP clock structure
>  * @scaled_ppm: Scaled parts per million adjustment from base
>  *
>  * Adjust the frequency of the PHC by the indicated delta from the base
>  * frequency.
>  *
>  * Scaled parts per million is ppm with a 16 bit binary fractional field.
>  **/
> static int i40e_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
> {
>         struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>         struct i40e_hw *hw = &pf->hw;
>         u64 adj, base_adj;
> 
>         smp_mb(); /* Force any pending update before accessing. */
>         base_adj = I40E_PTP_40GB_INCVAL * READ_ONCE(pf->ptp_adj_mult);
> 
>         adj = adjust_by_scaled_ppm(base_adj, scaled_ppm);
> 

Using adjust_by_scaled_ppm correctly performs the calculation and uses
the base adjustment, so there's no error here.

>         wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>         wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
> 
>         return 0;
> }


Thanks for finding and fixing this mistake. I think its the simplest fix
to get into the stable kernel that are broken, since taking the
adjust_by_scaled_ppm version would require additional patches.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Yajun Deng Sept. 25, 2023, 7:55 a.m. UTC | #2 
On 2023/6/28 04:20, Jacob Keller wrote:
>
> On 6/26/2023 7:26 PM, Yajun Deng wrote:
>> The new adjustment should be based on the base frequency, not the
>> I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().
>>
>> This issue was introduced in commit 3626a690b717 ("i40e: use
>> mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
>> commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
>> parts per million"). However the latter is a new feature and hasn't been
>> backported to the stable releases.
>>
>> This issue affects both v6.0 and v6.1 versions, and the v6.1 version is
>> an LTS version.
>>
>> Fixes: 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for PTP frequency calculation")
>> Cc: <stable@vger.kernel.org> # 6.1
>> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
>> ---
>>   drivers/net/ethernet/intel/i40e/i40e_ptp.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_ptp.c b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
>> index ffea0c9c82f1..97a9efe7b713 100644
>> --- a/drivers/net/ethernet/intel/i40e/i40e_ptp.c
>> +++ b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
>> @@ -361,9 +361,9 @@ static int i40e_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
>>   				   1000000ULL << 16);
>>   
>>   	if (neg_adj)
>> -		adj = I40E_PTP_40GB_INCVAL - diff;
>> +		adj = freq - diff;
>>   	else
>> -		adj = I40E_PTP_40GB_INCVAL + diff;
>> +		adj = freq + diff;
>>   
>>   	wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>>   	wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
> This straight forward fix makes sense. However, it wasn't obvious to me
> without context why the 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for
> PTP frequency calculation") was where the fault got introduced. Thus,
> here is that context for anyone else who failed to spot it just looking
> at shrunk patch diffs.
>
> --> code before that commit <---
>> /**
>>   * i40e_ptp_adjfreq - Adjust the PHC frequency
>>   * @ptp: The PTP clock structure
>>   * @ppb: Parts per billion adjustment from the base
>>   *
>>   * Adjust the frequency of the PHC by the indicated parts per billion from the
>>   * base frequency.
>>   **/
>> static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
>> {
>>          struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>>          struct i40e_hw *hw = &pf->hw;
>>          u64 adj, freq, diff;
>>          int neg_adj = 0;
>>
>>          if (ppb < 0) {
>>                  neg_adj = 1;
>>                  ppb = -ppb;
>>          }
>>
>>          freq = I40E_PTP_40GB_INCVAL;
> frequency is left just as base I40E_PTP_40GB_INCVAL.
>
>>          freq *= ppb;
>>          diff = div_u64(freq, 1000000000ULL);
>>
>>          if (neg_adj)
>>                  adj = I40E_PTP_40GB_INCVAL - diff;
>>          else
>>                  adj = I40E_PTP_40GB_INCVAL + diff;
>>
> So the base here can't be freq since we modify freq above using *=, but
> using I40E_PTP_40GB_INCVAL is consistent.
>
>>          /* At some link speeds, the base incval is so large that directly
>>           * multiplying by ppb would result in arithmetic overflow even when
>>           * using a u64. Avoid this by instead calculating the new incval
>>           * always in terms of the 40GbE clock rate and then multiplying by the
>>           * link speed factor afterwards. This does result in slightly lower
>>           * precision at lower link speeds, but it is fairly minor.
>>           */
>>          smp_mb(); /* Force any pending update before accessing. */
>>          adj *= READ_ONCE(pf->ptp_adj_mult);
>>
> Finally, the multiply is applied last. This affects the combined base +
> difference, and is done in order to avoid overflowing the *= used in the
> original implementation.
>
>>          wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>>          wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
>>
>>          return 0;
>> }
>
> ---> code after that commit <---
>> /**
>>   * i40e_ptp_adjfreq - Adjust the PHC frequency
>>   * @ptp: The PTP clock structure
>>   * @ppb: Parts per billion adjustment from the base
>>   *
>>   * Adjust the frequency of the PHC by the indicated parts per billion from the
>>   * base frequency.
>>   **/
>> static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
>> {
>>          struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>>          struct i40e_hw *hw = &pf->hw;
>>          u64 adj, freq, diff;
>>          int neg_adj = 0;
>>
>>          if (ppb < 0) {
>>                  neg_adj = 1;
>>                  ppb = -ppb;
>>          }
>>
>>          smp_mb(); /* Force any pending update before accessing. */
>>          freq = I40E_PTP_40GB_INCVAL * READ_ONCE(pf->ptp_adj_mult);
>>          diff = mul_u64_u64_div_u64(freq, (u64)ppb,
>>                                     1000000000ULL);
>>
> Here, we assign freq to be the I40E_PTP_40GB_INCVAL times the
> ptp_adj_mult value, and then we don't modify it, instead using
> mul_u64_u64_div_u64.
>
>>          if (neg_adj)
>>                  adj = I40E_PTP_40GB_INCVAL - diff;
>>          else
>>                  adj = I40E_PTP_40GB_INCVAL + diff;
>>
> But then the diff is applied on the wrong value, and no multiplication
> is done afterwards.
>
>>          wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>>          wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
>>
>>          return 0;
>> }
> ---> current version with adjust_by_scaled_ppm <---
>> /**
>>   * i40e_ptp_adjfine - Adjust the PHC frequency
>>   * @ptp: The PTP clock structure
>>   * @scaled_ppm: Scaled parts per million adjustment from base
>>   *
>>   * Adjust the frequency of the PHC by the indicated delta from the base
>>   * frequency.
>>   *
>>   * Scaled parts per million is ppm with a 16 bit binary fractional field.
>>   **/
>> static int i40e_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
>> {
>>          struct i40e_pf *pf = container_of(ptp, struct i40e_pf, ptp_caps);
>>          struct i40e_hw *hw = &pf->hw;
>>          u64 adj, base_adj;
>>
>>          smp_mb(); /* Force any pending update before accessing. */
>>          base_adj = I40E_PTP_40GB_INCVAL * READ_ONCE(pf->ptp_adj_mult);
>>
>>          adj = adjust_by_scaled_ppm(base_adj, scaled_ppm);
>>
> Using adjust_by_scaled_ppm correctly performs the calculation and uses
> the base adjustment, so there's no error here.
>
>>          wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
>>          wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
>>
>>          return 0;
>> }
>
> Thanks for finding and fixing this mistake. I think its the simplest fix
> to get into the stable kernel that are broken, since taking the
> adjust_by_scaled_ppm version would require additional patches.
>
> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
>
Kindly ping...
Tony Nguyen Sept. 25, 2023, 11:59 p.m. UTC | #3 
On 9/25/2023 12:55 AM, Yajun Deng wrote:
> 
> On 2023/6/28 04:20, Jacob Keller wrote:
>>
>> On 6/26/2023 7:26 PM, Yajun Deng wrote:
>>> The new adjustment should be based on the base frequency, not the
>>> I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().
>>>
>>> This issue was introduced in commit 3626a690b717 ("i40e: use
>>> mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
>>> commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
>>> parts per million"). However the latter is a new feature and hasn't been
>>> backported to the stable releases.
>>>
>>> This issue affects both v6.0 and v6.1 versions, and the v6.1 version is
>>> an LTS version.
>>>

...

>>
>> Thanks for finding and fixing this mistake. I think its the simplest fix
>> to get into the stable kernel that are broken, since taking the
>> adjust_by_scaled_ppm version would require additional patches.
>>
>> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
>>
> Kindly ping...

As this patch looks to be for stable, you need to follow the process for 
that. I believe your situation would fall into option 3:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-3

Thanks,
Tony
Yajun Deng Sept. 26, 2023, 1:54 a.m. UTC | #4 
On 2023/9/26 07:59, Tony Nguyen wrote:
> On 9/25/2023 12:55 AM, Yajun Deng wrote:
>>
>> On 2023/6/28 04:20, Jacob Keller wrote:
>>>
>>> On 6/26/2023 7:26 PM, Yajun Deng wrote:
>>>> The new adjustment should be based on the base frequency, not the
>>>> I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().
>>>>
>>>> This issue was introduced in commit 3626a690b717 ("i40e: use
>>>> mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
>>>> commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
>>>> parts per million"). However the latter is a new feature and hasn't 
>>>> been
>>>> backported to the stable releases.
>>>>
>>>> This issue affects both v6.0 and v6.1 versions, and the v6.1 
>>>> version is
>>>> an LTS version.
>>>>
>
> ...
>
>>>
>>> Thanks for finding and fixing this mistake. I think its the simplest 
>>> fix
>>> to get into the stable kernel that are broken, since taking the
>>> adjust_by_scaled_ppm version would require additional patches.
>>>
>>> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
>>>
>> Kindly ping...
>
> As this patch looks to be for stable, you need to follow the process 
> for that. I believe your situation would fall into option 3:
> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-3 
>
>
Yes, it needs an upstream commit ID. But this patch didn't need to apply 
to the upstream.

As the commit of the patch, the issue was fixed in
commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
parts per million"). However the commit is a new feature and hasn't been
backported to the stable releases.

Therefore, the patch does not have an upstream commit ID, and only needs 
to be applied to stable.


> Thanks,
> Tony
Greg KH Sept. 26, 2023, 4:47 a.m. UTC | #5 
On Tue, Sep 26, 2023 at 09:54:29AM +0800, Yajun Deng wrote:
> 
> On 2023/9/26 07:59, Tony Nguyen wrote:
> > On 9/25/2023 12:55 AM, Yajun Deng wrote:
> > > 
> > > On 2023/6/28 04:20, Jacob Keller wrote:
> > > > 
> > > > On 6/26/2023 7:26 PM, Yajun Deng wrote:
> > > > > The new adjustment should be based on the base frequency, not the
> > > > > I40E_PTP_40GB_INCVAL in i40e_ptp_adjfine().
> > > > > 
> > > > > This issue was introduced in commit 3626a690b717 ("i40e: use
> > > > > mul_u64_u64_div_u64 for PTP frequency calculation"), and was fixed in
> > > > > commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
> > > > > parts per million"). However the latter is a new feature and
> > > > > hasn't been
> > > > > backported to the stable releases.
> > > > > 
> > > > > This issue affects both v6.0 and v6.1 versions, and the v6.1
> > > > > version is
> > > > > an LTS version.
> > > > > 
> > 
> > ...
> > 
> > > > 
> > > > Thanks for finding and fixing this mistake. I think its the
> > > > simplest fix
> > > > to get into the stable kernel that are broken, since taking the
> > > > adjust_by_scaled_ppm version would require additional patches.
> > > > 
> > > > Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
> > > > 
> > > Kindly ping...
> > 
> > As this patch looks to be for stable, you need to follow the process for
> > that. I believe your situation would fall into option 3:
> > https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-3
> > 
> > 
> Yes, it needs an upstream commit ID. But this patch didn't need to apply to
> the upstream.
> 
> As the commit of the patch, the issue was fixed in
> commit 1060707e3809 ("ptp: introduce helpers to adjust by scaled
> parts per million"). However the commit is a new feature and hasn't been
> backported to the stable releases.
> 
> Therefore, the patch does not have an upstream commit ID, and only needs to
> be applied to stable.

That wasn't very obvious to most of us, perhaps resend it and explicitly
ask for acks/reviews so it can be only applied to the 6.1.y tree?

thanks,

greg k-h
diff mbox series

Patch

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ptp.c b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
index ffea0c9c82f1..97a9efe7b713 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ptp.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
@@ -361,9 +361,9 @@  static int i40e_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 				   1000000ULL << 16);
 
 	if (neg_adj)
-		adj = I40E_PTP_40GB_INCVAL - diff;
+		adj = freq - diff;
 	else
-		adj = I40E_PTP_40GB_INCVAL + diff;
+		adj = freq + diff;
 
 	wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);
 	wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);