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;
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