linux-kernel - Re: [iwl-net v1 1/2] igc: Fix missing time sync events

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Message-ID: <87y1bhok6k.fsf@kurt.kurt.home>
Date: Sun, 18 Feb 2024 16:40:03 +0100
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 intel-wired-lan@...ts.osuosl.org
Cc: sasha.neftin@...el.com, richardcochran@...il.com,
 anthony.l.nguyen@...el.com, jesse.brandeburg@...el.com, Vinicius Costa
 Gomes <vinicius.gomes@...el.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Jeff Kirsher
 <jeffrey.t.kirsher@...el.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [iwl-net v1 1/2] igc: Fix missing time sync events

On Fri Feb 16 2024, Vinicius Costa Gomes wrote:
> Fix "double" clearing of interrupts, which can cause external events
> or timestamps to be missed.
>
> The IGC_TSIRC Time Sync Interrupt Cause register can be cleared in two
> ways, by either reading it or by writing '1' into the specific cause
> bit. This is documented in section 8.16.1.
>
> The following flow was used:
>  1. read IGC_TSIRC into 'tsicr';
>  2. handle the interrupts present in 'tsirc' and mark them in 'ack';
>  3. write 'ack' into IGC_TSICR;
>
> As both (1) and (3) will clear the interrupt cause, if an interrupt
> happens between (1) and (3) it will be ignored, causing events to be
> missed.
>
> Remove the extra clear in (3).
>
> Fixes: 2c344ae24501 ("igc: Add support for TX timestamping")
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>

No obvious issues found while testing.

Reviewed-by: Kurt Kanzenbach <kurt@...utronix.de>
Tested-by: Kurt Kanzenbach <kurt@...utronix.de> # Intel i225

Thanks!

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