netdev - Re: [PATCH iwl-net v3 0/6] igc: Fix PTM timeout

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Message-ID: <ZzN2wIg6qE3_gAm4@calimero.vinschen.de>
Date: Tue, 12 Nov 2024 16:39:44 +0100
From: Corinna Vinschen <vinschen@...hat.com>
To: Christopher S M Hall <christopher.s.hall@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, david.zage@...el.com,
	vinicius.gomes@...el.com, netdev@...r.kernel.org,
	rodrigo.cadore@...coustics.com
Subject: Re: [PATCH iwl-net v3 0/6] igc: Fix PTM timeout

Hi Chris,

On Nov  6 18:47, Christopher S M Hall wrote:
> There have been sporadic reports of PTM timeouts using i225/i226 devices
> 
> These timeouts have been root caused to:
> 
> 1) Manipulating the PTM status register while PTM is enabled and triggered
> 2) The hardware retrying too quickly when an inappropriate response is
>    received from the upstream device
> 
> The issue can be reproduced with the following:
> 
> $ sudo phc2sys -R 1000 -O 0 -i tsn0 -m
> 
> Note: 1000 Hz (-R 1000) is unrealistically large, but provides a way to
> quickly reproduce the issue.
> 
> PHC2SYS exits with:
> 
> "ioctl PTP_OFFSET_PRECISE: Connection timed out" when the PTM transaction
>   fails
> 
> Additional problem description tested by:
> Corinna Vinschen <vinschen@...hat.com>
> 
>   This patch also fixes a hang in igc_probe() when loading the igc
>   driver in the kdump kernel on systems supporting PTM.
> 
>   The igc driver running in the base kernel enables PTM trigger in
>   igc_probe().  Therefore the driver is always in PTM trigger mode,
>   except in brief periods when manually triggering a PTM cycle.
> 
>   When a crash occurs, the NIC is reset while PTM trigger is enabled.
>   Due to a hardware problem, the NIC is subsequently in a bad busmaster
>   state and doesn't handle register reads/writes.  When running
>   igc_probe() in the kdump kernel, the first register access to a NIC
>   register hangs driver probing and ultimately breaks kdump.
> 
>   With this patch, igc has PTM trigger disabled most of the time,
>   and the trigger is only enabled for very brief (10 - 100 us) periods
>   when manually triggering a PTM cycle.  Chances that a crash occurs
>   during a PTM trigger are not zero, but extremly reduced.

The patchset looks good to me, but I don't see that this description
will make it into the commit message of patch 1.  Was that intended?

Other than that...

Reviewed-by: Corinna Vinschen <vinschen@...hat.com>


Thanks,
Corinna