Re: [PATCH v5 1/5] Bluetooth: hci_qca: use wait_until_sent() for power pulses

From: Johan Hovold <johan@kernel.org>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: Balakrishna Godavarthi <bgodavar@codeaurora.org>,
	marcel@holtmann.org, johan.hedberg@gmail.com, johan@kernel.org,
	linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org,
	hemantg@codeaurora.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v5 1/5] Bluetooth: hci_qca: use wait_until_sent() for power pulses
Date: Wed, 9 Jan 2019 15:38:22 +0100	[thread overview]
Message-ID: <20190109143822.GM14782@localhost> (raw)
In-Reply-To: <20181222015947.GF261387@google.com>

On Fri, Dec 21, 2018 at 05:59:47PM -0800, Matthias Kaehlcke wrote:
> On Thu, Dec 20, 2018 at 08:16:35PM +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@codeaurora.org>
> > ---
> >  drivers/bluetooth/hci_qca.c | 38 ++++++++++++++-----------------------
> >  1 file changed, 14 insertions(+), 24 deletions(-)
> > 
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index f036c8f98ea3..5a07c2370289 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -1013,11 +1013,9 @@ static inline void host_set_baudrate(struct hci_uart *hu, unsigned int speed)
> >  		hci_uart_set_baudrate(hu, speed);
> >  }
> >  
> > -static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
> > +static int qca_send_power_pulse(struct hci_uart *hu, 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
> > @@ -1029,19 +1027,16 @@ static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
> >  	 * save power. Disabling hardware flow control is mandatory while
> >  	 * 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;
> > -
> > +	bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
> >  	hci_uart_set_flow_control(hu, true);
> > +	ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd));
> > +	if (ret < 0) {
> > +		bt_dev_err(hu->hdev, "failed to send power pulse %02x to SoC",
> > +			   cmd);
> > +		return ret;
> > +	}
> >  
> > -	skb_put_u8(skb, cmd);
> > -	hci_skb_pkt_type(skb) = HCI_COMMAND_PKT;
> > -
> > -	skb_queue_tail(&qca->txq, skb);
> > -	hci_uart_tx_wakeup(hu);
> > +	serdev_device_wait_until_sent(hu->serdev, 0);

Again, do you really want to wait indefinitely here?

> serdev_device_wait_until_sent() might only guarantee that the UART
> circular buffer is empty (see
> https://elixir.bootlin.com/linux/v4.19/source/drivers/tty/tty_ioctl.c#L225),
> not that the data has actually sent (e.g. it might be sitting in
> the UART FIFO).

For serial core, uart_wait_until_sent() makes sure also the UART FIFO is
empty, although it may time out when using flow control (as then the
FIFO may never empty, and flow control appears to be enabled here).

Johan