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Subject: Re: [PATCH 4.16 REGRESSION fix 2/2] Bluetooth: hci_bcm: Set
 pulsed_host_wake flag in sleep parameters
From: Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20180314220603.7559-3-hdegoede@redhat.com>
Date: Thu, 15 Mar 2018 19:40:21 +0100
Cc: "Gustavo F. Padovan" <gustavo@padovan.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        =?utf-8?Q?Fr=C3=A9d=C3=A9ric_Danis?= <frederic.danis.oss@gmail.com>,
        Lukas Wunner <lukas@wunner.de>,
        linux-bluetooth@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-acpi@vger.kernel.org
Message-Id: <42ADB588-D50F-468A-9E42-7D991A78847A@holtmann.org>
References: <20180314220603.7559-1-hdegoede@redhat.com>
 <20180314220603.7559-3-hdegoede@redhat.com>
To: Hans de Goede <hdegoede@redhat.com>
Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Hans,

> 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@redhat.com>
> ---
> drivers/bluetooth/hci_bcm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

patch has been applied to bluetooth-stable tree.

Regards

Marcel