linux-kernel - Re: [PATCH v6 2/4] Add support for SCT Write Same

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Date:   Wed, 24 Aug 2016 14:10:06 +0800
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 2/4] Add support for SCT Write Same

Btw, I wonder if you need to memset your buffer with 0 first, like
what is done in ata_scsi_rbuf_get.

On 24 August 2016 at 13:57, Tom Yan <tom.ty89@...il.com> wrote:
> Never mind. I was a bit lightheaded.
>
> Anyway I don't think you should use ata_scsi_rbuf. It is a buffer
> created and used for ata_scsi_simulate, which interacts with the SCSI
> layer but not the ATA device (v.s. ata_scsi_translate). You should
> probably create buffer inside ata_format_dsm_trim_descr() and
> ata_format_sct_write_same() of size(s) you need.
>
> On 23 August 2016 at 18:56, Shaun Tancheff <shaun.tancheff@...gate.com> wrote:
>> On Tue, Aug 23, 2016 at 5:37 AM, Tom Yan <tom.ty89@...il.com> wrote:
>>> On 22 August 2016 at 04:23, Shaun Tancheff <shaun@...cheff.com> wrote:
>>>> +/**
>>>> + * ata_format_dsm_trim_descr() - SATL Write Same to ATA SCT Write Same
>>>> + * @cmd: SCSI command being translated
>>>> + * @lba: Starting sector
>>>> + * @num: Number of logical sectors to be zero'd.
>>>> + *
>>>> + * Rewrite the WRITE SAME descriptor to be an SCT Write Same formatted
>>>> + * descriptor.
>>>> + * NOTE: Writes a pattern (0's) in the foreground.
>>>> + *       Large write-same requents can timeout.
>>>> + */
>>>> +static void ata_format_sct_write_same(struct scsi_cmnd *cmd, u64 lba, u64 num)
>>>> +{
>>>> +       u16 *sctpg;
>>>> +       unsigned long flags;
>>>> +
>>>> +       spin_lock_irqsave(&ata_scsi_rbuf_lock, flags);
>>>> +       sctpg = ((void *)ata_scsi_rbuf);
>>>
>>> Because ata_scsi_rbuf is of a fixed size of ATA_SCSI_RBUF_SIZE.
>>>
>>> #define ATA_SCSI_RBUF_SIZE      4096
>>> ...
>>> static u8 ata_scsi_rbuf[ATA_SCSI_RBUF_SIZE];
>>>
>>>> +
>>>> +       put_unaligned_le16(0x0002,  &sctpg[0]); /* SCT_ACT_WRITE_SAME */
>>>> +       put_unaligned_le16(0x0101,  &sctpg[1]); /* WRITE PTRN FG */
>>>> +       put_unaligned_le64(lba,     &sctpg[2]);
>>>> +       put_unaligned_le64(num,     &sctpg[6]);
>>>> +       put_unaligned_le32(0u,      &sctpg[10]);
>>>> +
>>>> +       sg_copy_from_buffer(scsi_sglist(cmd), scsi_sg_count(cmd), sctpg, 512);
>>>
>>> You have no reason to use 512 here instead of ATA_SCSI_RBUF_SIZE this time.
>>
>> Ah .. because SCT Write Same is a fixed 512 byte transfer?
>> Ah .. because I only have 512 bytes to copy?
>>
>>>> +       spin_unlock_irqrestore(&ata_scsi_rbuf_lock, flags);
>>>> +}