linux-kernel - Re: [PATCH 2/3] [SCSI]: runtime resume parent for child's system-resume

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Date:	Wed, 14 Dec 2011 11:20:09 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Jeff Garzik <jgarzik@...ox.com>,
	James Bottomley <JBottomley@...allels.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/3] [SCSI]: runtime resume parent for child's system-resume

On Wed, Dec 14, 2011 at 11:18 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> [Patch description from Alan Stern]
>
> 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.
>
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>

Hi Alan,

May I add your SOB?

Thanks,
Lin Ming

> ---
>  drivers/scsi/scsi_pm.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
> index a633076..bf8bf79 100644
> --- a/drivers/scsi/scsi_pm.c
> +++ b/drivers/scsi/scsi_pm.c
> @@ -72,8 +72,17 @@ static int scsi_bus_resume_common(struct device *dev)
>  {
>        int err = 0;
>
> -       if (scsi_is_sdev_device(dev))
> +       if (scsi_is_sdev_device(dev)) {
> +               /*
> +                * Parent device may have runtime suspended as soon as
> +                * it is woken up during the system resume.
> +                *
> +                * Resume it on behalf of child.
> +                */
> +               pm_runtime_get_sync(dev->parent);
>                err = scsi_dev_type_resume(dev);
> +               pm_runtime_put_sync(dev->parent);
> +       }
>
>        if (err == 0) {
>                pm_runtime_disable(dev);
> --
> 1.7.2.5
>
> --
--
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