Re: [PATCH 4.16 REGRESSION fix 1/2] Revert "Bluetooth: hci_bcm: Streamline runtime PM code"

[Lukas Wunner <lukas@wunner.de>]

On Wed, Mar 14, 2018 at 11:06:02PM +0100, Hans de Goede wrote:
> This reverts commit 43fff7683468 ("Bluetooth: hci_bcm: Streamline runtime
> PM code"). The commit msg for this commit states "No functional change
> intended.", but replacing:
> 
>  pm_runtime_get();
>  pm_runtime_mark_last_busy();
>  pm_runtime_put_autosuspend();
> 
> with:
> 
>  pm_request_resume();
> 
> Does result in a functional change, pm_request_resume() only calls
> pm_runtime_mark_last_busy() if the device was suspended before the call.
> 
> This results in the following happening:
> 
> 1) Device is runtime suspended
> 2) Device drives host_wake IRQ logically high as it starts receiving data
> 3) bcm_host_wake() gets called, causes the device to runtime-resume,
>    current time gets marked as last_busy time
> 4) After 5 seconds the autosuspend timer expires and the dev autosuspends
>    as no one has been calling pm_runtime_mark_last_busy(), the device was
>    resumed during those 5 seconds, so all the pm_request_resume() calls
>    while receiving data and/or bcm_host_wake() calls were nops
> 5) If 4) happens while the device has (just received) data in its buffer to
>    be read by the host the IRQ line is *already* / still logically high
>    when we autosuspend and since we use an edge triggered IRQ, the IRQ
>    will never trigger, causing the device to get stuck in suspend
> 
> Therefor this commit has to be reverted, so that we avoid the device
> getting stuck in suspend.
> 
> Cc: Lukas Wunner <lukas@wunner.de>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Acked-by: Lukas Wunner <lukas@wunner.de>