Re: [PATCH v4 1/5] Bluetooth: hci_qca: use wait_until_sent() for power pulses

From: Balakrishna Godavarthi
Date: Tue Dec 18 2018 - 05:55:34 EST

Hi Johan,

On 2018-12-18 14:43, Johan Hovold wrote:
On Mon, Dec 17, 2018 at 07:43:26PM +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@xxxxxxxxxxxxxx>
* used serdev_device_write_buf() instead of serdev_device_write()

* no change.
* Updated function qca_send_power_pulse()
* addressed reviewer comments.

* initial patch

drivers/bluetooth/hci_qca.c | 37 +++++++++++++------------------------
1 file changed, 13 insertions(+), 24 deletions(-)

diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
index f036c8f98ea3..d8bc77c8c9b9 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;
+ }

As I mentioned earlier, serdev_device_write_buf() can buffer less than
sizeof(cmd) bytes if the tty driver's write buffer is full (and return
the number of bytes buffered).

How you want to deal with that is up to you and the bluetooth
maintainers, but I think you want to at least log it even if you choose
to ignore it.


[Bala]: thanks for reminding me for buffer size.
we use the qca_send_power_pulse() where we use serdev_write_buf() to send
a single byte commands to the chip during power ON or power OFF i.e. as soon as we open port or before close.

during power on:
ideally open port can guarantee me to the have tty buffer empty as we didn't queued any data.
let us assume that if the buffer is full(), serdev_device_write_buf() will return -1 (as buffer is full)
anyways i have check for return status to log the write_buf failure.

during power off:
yes here we may face an issue as already we have some data queued in the buffer. i.e. due to previous transactions.
I think we can achieve this by calling serdev_device_write_flush() and then calling serdev_device_write_buf().