linux-kernel - Re: [PATCH v1 1/4] Bluetooth: hci_qca: use wait_until

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Date:   Fri, 16 Nov 2018 10:47:24 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.org>
Cc:     Johan Hovold <johan@...nel.org>, marcel@...tmann.org,
        johan.hedberg@...il.com, mka@...omium.org,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org,
        Johan Hovold <jhovold@...il.com>
Subject: Re: [PATCH v1 1/4] Bluetooth: hci_qca: use wait_until_sent() for
 power pulses

On Thu, Nov 15, 2018 at 08:04:29PM +0530, Balakrishna Godavarthi wrote:
> Hi Johan,
> 
> On 2018-11-14 20:57, Johan Hovold wrote:
> > On Tue, Nov 06, 2018 at 05:35:25PM +0530, Balakrishna Godavarthi wrote:
> >> wcn3990 requires a power pulse to turn ON/OFF along with
> >> regulators. Sometimes we are observing the power pulses are sent
> >> out with some time delay, due to queuing these commands. This is
> >> causing synchronization issues with chip, which intern delay the
> >> chip setup or may end up with communication issues.
> >> 
> >> Signed-off-by: Balakrishna Godavarthi <bgodavar@...eaurora.org>
> >> ---
> >>  drivers/bluetooth/hci_qca.c | 22 +++++++++-------------
> >>  1 file changed, 9 insertions(+), 13 deletions(-)
> >> 
> >> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> >> index f72ded4ec9ae..051f081d1835 100644
> >> --- a/drivers/bluetooth/hci_qca.c
> >> +++ b/drivers/bluetooth/hci_qca.c
> >> @@ -1016,8 +1016,7 @@ static inline void host_set_baudrate(struct 
> >> hci_uart *hu, unsigned int speed)
> >>  static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
> >>  {
> >>  	struct hci_uart *hu = hci_get_drvdata(hdev);
> >> -	struct qca_data *qca = hu->priv;
> >> -	struct sk_buff *skb;
> >> +	int ret;
> >> 
> >>  	/* These power pulses are single byte command which are sent
> >>  	 * at required baudrate to wcn3990. On wcn3990, we have an external
> >> @@ -1030,18 +1029,14 @@ static int qca_send_power_pulse(struct hci_dev 
> >> *hdev, u8 cmd)
> >>  	 * sending power pulses to SoC.
> >>  	 */
> >>  	bt_dev_dbg(hdev, "sending power pulse %02x to SoC", cmd);
> >> -
> >> -	skb = bt_skb_alloc(sizeof(cmd), GFP_KERNEL);
> >> -	if (!skb)
> >> -		return -ENOMEM;
> >> -
> >>  	hci_uart_set_flow_control(hu, true);
> >> +	ret = serdev_device_write(hu->serdev, &cmd, sizeof(cmd), 0);
> > 
> > Don't you want a non-zero timeout here? Otherwise you might as well
> > call serdev_device_write() directly.
> 
> [Bala]: we need an in definite timeout for these commands. will use 
> HCI_UART_TX_WAKEUP.
> 
> > Also have you made sure that serdev_device_write_wakeup() is called in
> > the drivers write-wakeup callback as serdev_device_write() requires?
> > 
> > See this series in case what you really wanted was to wait indefinitely
> > (you can use MAX_SCHEDULE_TIMEOUT):
> > 
> > 	https://lkml.kernel.org/r/<20181114150904.19653-1-johan@...nel.org>
> 
> [Bala]: thanks for pointers. from 
> https://lore.kernel.org/patchwork/patch/1012358/
>          it was clear to me that i need call below functions in order to 
> wait until full data is sent.
> 
>          serdev_device_write_wakeup()
>          serdev_device_write()
>          serdev_device_wait_until_sent()
> 
>          correct me whether my understanding is correct.

No, serdev_device_write_wakeup() needs to be called from the serdev
driver's write_wakeup() callback (as defined in struct struct
serdev_device_ops).

Either use serdev_device_write_wakeup() as the callback, or call it from
your driver's custom write_wakeup() callback.

Hmm, I see now that the callbacks are set in hci_uart_register_device()
to hci_serdev_client_ops, which is shared by all serdev BT drivers. You
may be able to just add the call to the callback defined there so that
all Bluetooth drivers can use serdev_device_write().

Johan