linux-kernel - Re: [PATCH RESEND] i40e: fix the wrong PTP frequency calculation

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Message-ID: <2023100707-hydrogen-tapestry-62e8@gregkh>
Date:   Sat, 7 Oct 2023 13:33:17 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
Cc:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        jacob.e.keller@...el.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH RESEND] i40e: fix the wrong PTP frequency calculation

On Tue, Sep 26, 2023 at 03:10:59PM +0800, 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"), frequency is left
> just as base I40E_PTP_40GB_INCVAL before the commit. After the commit,
> frequency is the I40E_PTP_40GB_INCVAL times the ptp_adj_mult value.
> But then the diff is applied on the wrong value, and no multiplication
> is done afterwards.
> 
> It was accidentally fixed in commit 1060707e3809 ("ptp: introduce helpers
> to adjust by scaled parts per million"). It uses adjust_by_scaled_ppm
> correctly performs the calculation and uses the base adjustment, so
> there's no error here. But it is a new feature and doesn't need to
> backported to the stable releases.
> 
> This issue affects both v6.0 and v6.1, and the v6.1 version is an LTS
> release. Therefore, the patch only needs to be applied to v6.1 stable.
> 
> Fixes: 3626a690b717 ("i40e: use mul_u64_u64_div_u64 for PTP frequency calculation")
> Cc: <stable@...r.kernel.org> # 6.1
> Cc: Tony Nguyen <anthony.l.nguyen@...el.com>
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_ptp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Now queued up, thanks.

greg k-h