On Fri, Sep 14, 2012 at 09:54:16PM +0800, Aaron Lu wrote:
> On Fri, Sep 14, 2012 at 11:26:29AM +0100, James Bottomley wrote:
> > On Fri, 2012-09-14 at 16:48 +0800, Aaron Lu wrote:
> > > So if we program the device to let it enter standby/stopped power
> > > condition with the start_stop_unit command, do we need to sync the
> > > cache?
> >
> > No, that's what the spec says. The device must manage the cache in both
> > the forced (start stop unit) and timed (power control mode page) cases.
> >
> > The reason is the spec doesn't define what idle and standby actually
> > mean (just that they're "lower" power states). So the device
> > implementers get to choose if they stop the platter or power off the
> > motor. The spec just means that if they do anything that causes danger
> > to data in the cache, they have to deal with it themselves.
>
> Thanks for the clear explanation.
>
> So what about the following change? In sd_suspend, if device supports
> start_stop command, then we just need issue this command then both
> runtime suspend case and system S3/S4 case are OK, since when the device
> enters stopped power condition, the internal cache should be taken care
> of by the device and it is also ready to be powered off. And if device
This is not the case for ata device, so scsi stop command should
translate to 2 ata commands: flush cache + enter standby.
If flush cache is skipped in sd driver, then ata scsi translate will
need to update to address this issue.
A possible change(not tested) like this:
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 8ec81ca..2de5fac 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -1759,6 +1759,19 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
ata_qc_free(qc);
}
+static int ata_flush_cache(struct ata_device *dev)
+{
+ u8 cmd;
+
+ if (dev->flags & ATA_DFLAG_FLUSH_EXT)
+ cmd = ATA_CMD_FLUSH_EXT;
+ else
+ cmd = ATA_CMD_FLUSH;
+
+ return ata_do_simple_cmd(dev, cmd);
+}
+
+
/**
* ata_scsi_translate - Translate then issue SCSI command to ATA device
* @dev: ATA device to which the command is addressed
@@ -1816,6 +1829,13 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
if (xlat_func(qc))
goto early_finish;
+ /* scsi stop cmd = flush cache + standby */
+ if (qc->tf.command == ATA_CMD_STANDBYNOW1 && ata_try_flush_cache(dev)) {
+ rc = ata_flush_cache(dev);
+ if (rc)
+ goto err_did;
+ }
+
if (ap->ops->qc_defer) {
if ((rc = ap->ops->qc_defer(qc)))
goto defer;
Thanks,
Aaron
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