On Wed, Mar 14, 2018 at 11:06:03PM +0100, Hans de Goede wrote:
> The IRQ output of the bcm bt-device is really a level IRQ signal, which
> signals a logical high as long as the device's buffer contains data. Since
> the draining in the buffer is done in the tty driver, we cannot (easily)
> wait in a threaded interrupt handler for the draining, after which the
> IRQ should go low again.
>
> So instead we treat the IRQ as an edge interrupt. This opens the window
> for a theoretical race where we wakeup, read some data and then autosuspend
> *before* the IRQ has gone (logical) low, followed by the device just at
> that moment receiving more data, causing the IRQ to stay high and we never
> see an edge.
>
> Since we call pm_runtime_mark_last_busy() on every received byte, there
> should be plenty time for the IRQ to go (logical) low before we ever
> suspend, so this should never happen, but after commit 43fff7683468
> ("Bluetooth: hci_bcm: Streamline runtime PM code"), which has been reverted
> since, this was actually happening causing the device to get stuck in
> runtime suspend.
>
> The bcm bt-device actually has a workaround for this, if we set the
> pulsed_host_wake flag in the sleep parameters, then the device monitors
> if the host is draining the buffer and if not then after a timeout the
> device will pulse the IRQ line, causing us to see an edge, fixing the
> stuck in suspend condition.
>
> This commit sets the pulsed_host_wake flag to fix the (mostly theoretical)
> race caused by us treating the IRQ as an edge IRQ.
>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>
Good work, thanks.
> ---
> drivers/bluetooth/hci_bcm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/bluetooth/hci_bcm.c b/drivers/bluetooth/hci_bcm.c
> index b089012a49f9..04b9a6c75c75 100644
> --- a/drivers/bluetooth/hci_bcm.c
> +++ b/drivers/bluetooth/hci_bcm.c
> @@ -307,7 +307,7 @@ static const struct bcm_set_sleep_mode default_sleep_params = {
> .usb_auto_sleep = 0,
> .usb_resume_timeout = 0,
> .break_to_host = 0,
> - .pulsed_host_wake = 0,
> + .pulsed_host_wake = 1,
> };
>
> static int bcm_setup_sleep(struct hci_uart *hu)
> --
> 2.14.3
>
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