(resending due to GMail mess-up, sorry) On Mon, Mar 11, 2013 at 2:49 AM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 2013-03-11 at 11:42 +0800, Aaron Lu wrote: >> Hi all, >> >> I've seen some reports on STANDBY IMMEDIATE failed on NVIDIA MCP5x >> controllers when system goes to suspend(this command is sent by scsi sd >> driver on system suspend as a SCSI STOP command, which is translated to >> STANDBY IMMEDIATE ATA command). I've no idea of why this happened, so >> I wrote this email in hope of getting some new idea. >> >> The related bug report: >> https://bugzilla.kernel.org/show_bug.cgi?id=48951 >> >> And google search showed that Peter reported a similar problem here: >> http://marc.info/?l=linux-ide&m=133534061316338&w=2 >> >> And bladud has found that, disable asyn suspend for the scsi target >> device can work around this problem. >> >> Please feel free to suggest what can possibly be the cause, thanks. > > I sometimes despair of people getting PM stuff right. What on earth is > the point of refusing to suspend if the disk refuses to stop? In theory > it gives the device more time to park its head, but almost no modern > drive requires this. The next action suspend will take (if allowed) is > to power down peripherals which will forcibly stop the device. The stop > request is purely informational for the device. If it ignores it, then > the bigger hammer still works. This really does matter. Especially on laptop hard drives (but on many desktop ones as well), we really want to stop the drive, and therefore unload the heads, before the power is shut off. Drives are often rated for a much lower number of emergency head unloads (caused by power loss) over their lifespan than normal software-commanded ones. So over a long period of time, repeatedly failing to stop the drive before power off will shorten its life. Maybe aborting suspend for this is a bit harsh but it's not something that should be ignored. Just to add to this point, it doesn't just matter for rotational drives, either. A lot of SSDs use the "standby now" command to do some kind of cleanup before power off. Some drives document that a subsequent power up may take longer for the drive to be ready if it wasn't "spun down" prior to the last power off. It's conceivable that in some crappy drives, lack of proper power-off sequence could even cause data loss. The question is, at the point where we are stopping the drive, has anything been done to the ATA controller to suspend it? If so, that sounds like a definite bug somewhere. It has to be something we are doing on the kernel side, otherwise why would this work if async suspend was disabled? > > You really need to discriminate better between conditions we should and > shouldn't care about for suspend. so in sd_suspend, we definitely care > if we can't flush the cache of a write back device because the power off > could lose data. We don't really care if the disk says I can't stop, so > this is probably the correct fix. > > James > > --- > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c > index 7992635..384b621d 100644 > --- a/drivers/scsi/sd.c > +++ b/drivers/scsi/sd.c > @@ -3079,7 +3079,11 @@ static int sd_suspend(struct device *dev) > > if (sdkp->device->manage_start_stop) { > sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n"); > - ret = sd_start_stop_device(sdkp, 0); > + /* > + * this is informational for the disk we're going to power it > + * off anyway, so don't bother about the return status > + */ > + sd_start_stop_device(sdkp, 0); > } > > done: > > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
