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Date:   Sun, 3 May 2020 23:46:27 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, kernel@...gutronix.de
Subject: Re: [PATCH v2] libata: Fix retrieving of active qcs

On Monday 27 January 2020 12:24:28 Sascha Hauer wrote:
> On Mon, Jan 27, 2020 at 12:16:30PM +0100, Pali Rohár wrote:
> > On Monday 06 January 2020 09:16:05 Sascha Hauer wrote:
> > > On Wed, Dec 25, 2019 at 07:18:40PM +0100, 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 equation is no longer valid.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?
> > > 
> > > It's in nv_swncq_sdbfis(). Here we have:
> > > 
> > > 	sactive = readl(pp->sactive_block);
> > > 	done_mask = pp->qc_active ^ sactive;
> > > 
> > > 	pp->qc_active &= ~done_mask;
> > > 	pp->dhfis_bits &= ~done_mask;
> > > 	pp->dmafis_bits &= ~done_mask;
> > > 	pp->sdbfis_bits |= done_mask;
> > > 	ata_qc_complete_multiple(ap, ap->qc_active ^ done_mask);
> > > 
> > > Sascha
> > 
> > Ok. Are you going to fix also this case?
> 
> As said, this one looks slightly different than the others and I would
> prefer if somebody could fix it who actually has a hardware and can test
> it.

Well, I have hardware and could test changes. But I'm not really sure
that I understand this part of code. So it would be better if somebody
else with better knowledge prepares patches I could test them. But
currently during coronavirus I have only remote ssh access, so boot,
modify/compile/reboot process is quite slower.

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