Re: [PATCH 6/6] USB / PM: Allow USB devices to remain runtime-suspended when sleeping
From: Tomeu Vizoso
Date: Fri Apr 03 2015 - 09:06:24 EST
On 31 March 2015 at 19:09, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 31 Mar 2015, Tomeu Vizoso wrote:
>> Have dev_pm_ops.prepare return 1 for USB devices, interfaces, endpoints
>> and ports so that USB devices can remain runtime-suspended when the
>> system goes to a sleep state.
>> Also enable runtime PM for endpoints, which is another requirement for
>> the above to work.
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
>> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
>> index b1fb9ae..1498faa 100644
>> --- a/drivers/usb/core/usb.c
>> +++ b/drivers/usb/core/usb.c
>> @@ -300,7 +300,7 @@ static int usb_dev_uevent(struct device *dev, struct kobj_uevent_env *env)
>> static int usb_dev_prepare(struct device *dev)
>> - return 0; /* Implement eventually? */
>> + return 1; /* Implement eventually? */
> The rest of the patch is okay, but this part is wrong. The documented
> requirement is that the prepare callback should return 1 if the device
> is already in the appropriate state. This means it has to have the
> right wakeup setting.
> In other words, if the device is currently in runtime suspend with
> remote wakeup enabled, but device_may_wakeup() returns 0 (so that the
> device should be disabled for wakeup when the system goes into
> suspend), then the prepare callback has to return 0.
> Therefore what you need to do here is something like this:
> struct usb_device *udev = to_usb_device(dev);
> /* Return 0 if the current wakeup setting is wrong, otherwise 1 */
> if (udev->do_remote_wakeup && !device_may_wakeup(dev))
> return 0;
> return 1;
Thanks, in v2 I have also covered the other case, as suggested by Oliver.
> Aside from this issue, I like the patch set. Do you think you can do
> something similar for drivers/scsi/scsi_pm.c? I'm not aware of any
> wakeup-capable SCSI devices -- not disk or CD/DVD drives, anyway.
I think I will be able to allocate some time on monday to look at this.
> Alan Stern
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