2023-06-27 02:57:26

by Yajun Deng

[permalink] [raw]
Subject: [PATCH] i40e: fix the wrong PTP frequency calculation

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: <[email protected]> # 6.1
Signed-off-by: Yajun Deng <[email protected]>
---
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);
--
2.25.1



2023-06-27 20:49:37

by Jacob Keller

[permalink] [raw]
Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation



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: <[email protected]> # 6.1
> Signed-off-by: Yajun Deng <[email protected]>
> ---
> 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 <[email protected]>


2023-09-25 10:23:58

by Yajun Deng

[permalink] [raw]
Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation


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: <[email protected]> # 6.1
>> Signed-off-by: Yajun Deng <[email protected]>
>> ---
>> 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 <[email protected]>
>
Kindly ping...

2023-09-26 01:54:47

by Yajun Deng

[permalink] [raw]
Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation


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 <[email protected]>
>>>
>> 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

2023-09-26 05:19:30

by Tony Nguyen

[permalink] [raw]
Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation

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 <[email protected]>
>>
> 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

2023-09-26 05:54:47

by Greg Kroah-Hartman

[permalink] [raw]
Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation

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 <[email protected]>
> > > >
> > > 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