Re: [RFC PATCH] libata: scsi: flush cache on scsi stop command

[Gwendal Grignou <gwendal@google.com>]

On Wed, Sep 19, 2012 at 1:56 AM, Aaron Lu <aaron.lu@intel.com> wrote:
> scsi stop command is used to put a device into stopped power
> condition, and scsi devices will take care of its internal cache
> before entering this power condition. For ata devices, this command
> should be translated to flush cache + standby immediate, currently,
> we are translating it to only standby.
>
> This patch handle this by sending flush cache command when standby is
> to be sent, and in its qc complete function, send the actual standby.
>
> This patch will be used to support poweroff hard disk either when
> runtime or when system is going to S3/S4/S5. The sd_suspend will be
> modified to only send a stop command to the device if device manages
> start_stop, the current implementation will send a sync cache command,
> which is not necessary per the scsi spec.
>
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> ---
>  drivers/ata/libata-scsi.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 8ec81ca..de6e734 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -1759,6 +1759,27 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
>         ata_qc_free(qc);
>  }
>
> +static void ata_flush_qc_complete(struct ata_queued_cmd *qc)
> +{
> +       if (qc->err_mask) {
> +               ata_gen_ata_sense(qc);
> +               qc->scsidone(qc->scsicmd);
> +               ata_qc_free(qc);
> +       } else {
> +               qc->complete_fn = ata_scsi_qc_complete;
> +               qc->tf.command = ATA_CMD_STANDBYNOW1;
> +               ata_qc_issue(qc);
> +       }
> +}
> +
> +static void ata_qc_issue_flush(struct ata_queued_cmd *qc)
> +{
> +       qc->complete_fn = ata_flush_qc_complete;
> +       qc->tf.command = qc->dev->flags & ATA_DFLAG_FLUSH_EXT ?
> +                               ATA_CMD_FLUSH_EXT : ATA_CMD_FLUSH;
> +       ata_qc_issue(qc);
> +}
> +
>  /**
>   *     ata_scsi_translate - Translate then issue SCSI command to ATA device
>   *     @dev: ATA device to which the command is addressed
> @@ -1821,8 +1842,15 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
>                         goto defer;
>         }
>
> -       /* select device, send command to hardware */
> -       ata_qc_issue(qc);
> +       /*
> +        * If we received scsi stop command,
> +        * we will need to flush cache first
> +        */
> +       if (qc->tf.command == ATA_CMD_STANDBYNOW1 && ata_try_flush_cache(dev))
You are adding tests on the data path.
What about changing the xlat function ata_scsi_start_stop_xlat to -
when stop is requested:
- if try_flush_cache is true,
 change qc->complete_fn to ata_flush_qc_complete
 build a flush command
- else
 do as usual.

ata_flush_qc_complete remains the same.

> +               ata_qc_issue_flush(qc);
> +       else
> +               /* select device, send command to hardware */
> +               ata_qc_issue(qc);
>
>         VPRINTK("EXIT\n");
>         return 0;
> --
> 1.7.12.21.g871e293
>
> --
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