Re: [PATCH 2/3] scsi: pm80xx: Do not issue hard reset before NCQ EH

[Niklas Cassel <cassel@kernel.org>]

Hello Igor, TJ,

On Fri, Jun 07, 2024 at 05:57:42PM +0000, TJ Adams wrote:
> From: Igor Pylypiv <ipylypiv@google.com>
> 
> v6.2 commit 811be570a9a8 ("scsi: pm8001: Use sas_ata_device_link_abort()

Do not specify kernel version (it is irrelevant), SHA1 is enough.


> to handle NCQ errors") removed duplicate NCQ EH from the pm80xx driver
> and started relying on libata to handle the NCQ errors. The PM8006
> controller has a special EH sequence that was added in v4.15 commit
> 869ddbdcae3b ("scsi: pm80xx: corrected SATA abort handling sequence.").

Do not specify kernel version (it is irrelevant), SHA1 is enough.

Since the code added in 869ddbdcae3b still exists in the pm80xx driver,
I think that you should mention the commits in chronological order.
(Right now you mention the oldest still existing code last, which seems
a bit backwards.)


> The special EH sequence issues a hard reset to a drive before libata EH
> has a chance to read the NCQ log page. Libata EH gets confused by empty
> NCQ log page which results in HSM violation. The failed command gets
> retried a few times and each time fails with the same HSM violation.
> Finally, libata decides to disable NCQ due to subsequent HSM vioaltions.

s/vioaltions/violations/

I'm not an expert in libsas EH, but I think that your commit message fails
to explain why this change actually fixes anything. You do not mention the
relationship between the code that you add pm8001_work_fn() and the
existing code in pm8001_abort_task(), and the order in which the functions
get executed.

Does calling sas_execute_internal_abort_dev() from pm8001_work_fn() ensure
that the libsas EH is never invoked? Or does it cancel the hard reset that
is part of the "special EH sequence" in pm8001_abort_task() ?

Wouldn't it be better if this was fixed in pm8001_abort_task() or similar
instead? It appears that the code you add to pm8001_work_fn() (that has a
very ugly if (pm8006)) is only there to undo or avoid the hard reset that
is done in pm8001_abort_task() (which also has a very ugly if (pm8006)).

Now we have this ugly if (pm8006) in two different functions... which
makes my "this could be solved in a nicer way" detector go off.

If this patch (as is) is really the way to go, then I think there should
be a more detailed reasoning why this change is the most sensible one.


Kind regards,
Niklas