From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 613086FCF for ; Mon, 25 Sep 2023 07:55:37 +0000 (UTC) Received: from out-205.mta1.migadu.com (out-205.mta1.migadu.com [95.215.58.205]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 34966B3 for ; Mon, 25 Sep 2023 00:55:34 -0700 (PDT) Message-ID: <72bfc00f-7c60-f027-61cb-03084021c218@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695628532; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=l4uaK2NAz0kQWXVGJqJdnSvIF01RSrsxRcBRw98P7Xo=; b=v5hhDL2M9ia8zckH0z93X+e58vN0PpXpaidx8X8FRZpIZ1QpmwFZqng2W2ZU2b2AMJ0F7a oEE76dGg7Gl8gLZdlLYKF+Jsooxcul0wSkHM/o5k7DWjZ/ax2CmlBZKPqCjS8s4uzYZEi0 IpY7rKKhWdmTx807Fcueu9Sbx2pIxqI= Date: Mon, 25 Sep 2023 15:55:21 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] i40e: fix the wrong PTP frequency calculation Content-Language: en-US To: Jacob Keller , jesse.brandeburg@intel.com, anthony.l.nguyen@intel.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, richardcochran@gmail.com Cc: intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20230627022658.1876747-1-yajun.deng@linux.dev> <10269e86-ed8a-0b09-a39a-a5239a1ba744@intel.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yajun Deng In-Reply-To: <10269e86-ed8a-0b09-a39a-a5239a1ba744@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net 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: # 6.1 >> Signed-off-by: Yajun Deng >> --- >> 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 > Kindly ping...