linux-kernel - Re: [PATCH] Bluetooth: hci

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Date:   Mon, 4 Nov 2019 15:19:50 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Claire Chang <tientzu@...omium.org>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        Balakrishna Godavarthi <bgodavar@...eaurora.org>,
        Rocky Liao <rjliao@...eaurora.org>,
        Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: hci_qca: add PM support

Hi Claire,

> Add PM suspend/resume callbacks for hci_qca driver.
> 
> BT host will make sure both Rx and Tx go into sleep state in
> qca_suspend. Without this, Tx may still remain in awake state, which
> prevents BTSOC from entering deep sleep. For example, BlueZ will send
> Set Event Mask to device when suspending and this will wake the device
> Rx up. However, the Tx idle timeout on the host side is 2000 ms. If the
> host is suspended before its Tx idle times out, it won't send
> HCI_IBS_SLEEP_IND to the device and the device Rx will remain awake.
> 
> We implement this by canceling relevant work in workqueue, sending
> HCI_IBS_SLEEP_IND to the device and then waiting HCI_IBS_SLEEP_IND sent
> by the device.
> 
> In order to prevent the device from being awaken again after qca_suspend
> is called, we introduce QCA_SUSPEND flag. QCA_SUSPEND is set in the
> beginning of qca_suspend to indicate system is suspending and that we'd
> like to ignore any further wake events.
> 
> With QCA_SUSPEND and spinlock, we can avoid race condition, e.g. if
> qca_enqueue acquires qca->hci_ibs_lock before qca_suspend calls
> cancel_work_sync and then qca_enqueue adds a new qca->ws_awake_device
> work after the previous one is cancelled.
> 
> If BTSOC wants to wake the whole system up after qca_suspend is called,
> it will keep sending HCI_IBS_WAKE_IND and uart driver will take care of
> waking the system. For example, uart driver will reconfigure its Rx pin
> to a normal GPIO pin and enable irq wake on that pin when suspending.
> Once host detects Rx falling, the system will begin resuming. Then, the
> BT host clears QCA_SUSPEND flag in qca_resume and begins dealing with
> normal HCI packets. By doing so, only a few HCI_IBS_WAKE_IND packets are
> lost and there is no data packet loss.
> 
> Signed-off-by: Claire Chang <tientzu@...omium.org>
> ---
> drivers/bluetooth/hci_qca.c | 127 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 124 insertions(+), 3 deletions(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel