linux-kernel - Re: [PATCH v2] libata: Fix retrieving of active qcs

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Date:   Wed, 25 Dec 2019 19:36:01 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Sascha Hauer <s.hauer@...gutronix.de>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH v2] libata: Fix retrieving of active qcs

On Wednesday 25 December 2019 11:26:47 Jens Axboe wrote:
> On 12/25/19 11:18 AM, Pali Rohár wrote:
> > Hello Sascha!
> > 
> > On Friday 13 December 2019 09:04:08 Sascha Hauer wrote:
> >> ata_qc_complete_multiple() is called with a mask of the still active
> >> tags.
> >>
> >> mv_sata doesn't have this information directly and instead calculates
> >> the still active tags from the started tags (ap->qc_active) and the
> >> finished tags as (ap->qc_active ^ done_mask)
> >>
> >> Since 28361c40368 the hw_tag and tag are no longer the same and the
> >> equation is no longer valid. In ata_exec_internal_sg() ap->qc_active is
> >> initialized as 1ULL << ATA_TAG_INTERNAL, but in hardware tag 0 is
> >> started and this will be in done_mask on completion. ap->qc_active ^
> >> done_mask becomes 0x100000000 ^ 0x1 = 0x100000001 and thus tag 0 used as
> >> the internal tag will never be reported as completed.
> >>
> >> This is fixed by introducing ata_qc_get_active() which returns the
> >> active hardware tags and calling it where appropriate.
> >>
> >> This is tested on mv_sata, but sata_fsl and sata_nv suffer from the same
> >> problem. There is another case in sata_nv that most likely needs fixing
> >> as well, but this looks a little different, so I wasn't confident enough
> >> to change that.
> > 
> > I can confirm that sata_nv.ko does not work in 4.18 (and new) kernel
> > version correctly. More details are in email:
> > 
> > https://lore.kernel.org/linux-ide/20191225180824.bql2o5whougii4ch@pali/T/
> > 
> > I tried this patch and it fixed above problems with sata_nv.ko. It just
> > needs small modification (see below).
> > 
> > So you can add my:
> > 
> > Tested-by: Pali Rohár <pali.rohar@...il.com>
> > 
> > And I hope that patch would be backported to 4.18 and 4.19 stable
> > branches soon as distributions kernels are broken for machines with
> > these nvidia sata controllers.
> > 
> > Anyway, what is that another case in sata_nv which needs to be fixed
> > too?
> 
> Thanks for testing, I've applied this for 5.5 and marked it for stable.

It is this one?
https://git.kernel.dk/cgit/linux-block/commit/?h=libata-5.5&id=d80f359d0ebddb3ab3e9cc3fe96f244827ae7b09

Because there is missing EXPORT_SYMBOL_GPL for ata_qc_get_active()
function as I wrote in previous email.

-- 
Pali Rohár
pali.rohar@...il.com

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