linux-kernel - Re: [PATCH v6 3/4] SCT Write Same / DSM Trim

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Date:   Mon, 22 Aug 2016 20:57:52 +0000
From:   Tom Yan <tom.ty89@...il.com>
To:     Shaun Tancheff <shaun.tancheff@...gate.com>
Cc:     Shaun Tancheff <shaun@...cheff.com>, linux-ide@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Hellwig <hch@....de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Damien Le Moal <damien.lemoal@...t.com>,
        Hannes Reinecke <hare@...e.de>,
        Josh Bingaman <josh.bingaman@...gate.com>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH v6 3/4] SCT Write Same / DSM Trim

On 22 August 2016 at 18:52, Tom Yan <tom.ty89@...il.com> wrote:
>
> For the "payload block size" that is "always" 512-byte as per the same
> spec, I don't think we need to concern about it. I think it only
> matters if we want to enable multi-block TRIM payload according to the
> reported limit in IDENTIFY DEVICE data. Probably it merely means that
> the "each of the blocks" in the reported limit will always mean 64
> TRIM entries, even on 4Kn drives, instead of 512.
>

Actually that's what we assumed in our current code that forms the DSM
command as well. See how (hob_)feature for queued TRIM and how
(hob_)nsect for non-queued TRIM are set in ata_scsi_write_same_xlat in
libata-scsi ('size / 512').

So if you are going to increase the payload block size per logical
sector size (in other word, you assume that the payload block size is
_expected_ to be the logical block size, in spite of what ACS told,
you'll need to adjust how the aforementioned fields in the ATA
taskfile are set as well.