Re: [PATCH v5 5/6] ata: add ata port system PM callbacks

Lin Ming
2011-12-13T18:59:27Z

On Tue, 2011-12-13 at 23:47 +0800, Alan Stern wrote:
> On Tue, 13 Dec 2011, Lin Ming wrote:
>
> > I just realized that the ata port runtime PM status need to be updated
> > after system resume.
> >
> > I tried below patch.
> > Unfortunately, it causes a problem that sd can't resume correctly.
> >
> > During system resume, ata port is resumed first and then sd resumed.
> >
> > When ata port resumed, device_resume(...) calls pm_runtime_put_sync(..),
> > which causes ata port to be runtime suspended immediately.
> >
> > So sd resume fails because it requires ata port to be active to handle
> > start device command.
> >
> > This seems a PM core's bug.
> >
> > device_resume(...) should not runtime suspend the parent device, because
> > its children have not resumed yet.
> >
> > Alan,
> >
> > What do you think?
>
> This appears to be the first time this problem has come up. But it is
> a real problem.
>
> If a child device was runtime-suspended when a system suspend began,
> then there will be nothing to prevent its parent from
> runtime-suspending as soon as it is woken up during the system resume.
> Then when the time comes to resume the child, the resume will fail
> because the parent is already back at low power.
>
> On the other hand, there are some devices which should remain at low
> power across an entire suspend-resume cycle. The details depend on the
> device and the platform.
>
> This suggests that the PM core is not the right place to solve the
> problem. One possible solution is for the subsystem or device driver
> to call pm_runtime_get_sync(dev->parent) at the start of the
> system-resume procedure and pm_runtime_put_sync(dev->parent) at the
> end.

How about below?
(Not tested yet)

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index a633076..5cf9a19 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -71,9 +71,17 @@ static int scsi_bus_suspend_common(struct device *dev, pm_message_t msg)
static int scsi_bus_resume_common(struct device *dev)
{
int err = 0;
+ bool put = false;

- if (scsi_is_sdev_device(dev))
+ if (scsi_is_sdev_device(dev)) {
+ if (dev->parent && pm_runtime_suspended(dev->parent)) {
+ pm_runtime_get_sync(dev->parent);
+ put = true;
+ }
err = scsi_dev_type_resume(dev);
+ if (put)
+ pm_runtime_put_sync(dev->parent);
+ }

if (err == 0) {
pm_runtime_disable(dev);

>
> Alan Stern
>