Re: [PATCH v8 1/3] Bluetooth: hci_qca: use wait_until_sent() for power pulses

From: Balakrishna Godavarthi
Date: Thu Jan 17 2019 - 05:25:21 EST

Hi Matthias,

On 2019-01-17 01:52, Matthias Kaehlcke wrote:
On Wed, Jan 16, 2019 at 05:16:01PM +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>
Changes in v8:
* Updated 1 second timeout instead of indefinite wait.

Changes in v7:
* updated the wait time to 5 ms after sending power pulses.

Changes in v6:
* added serdev_device_write_flush() in qca_send_power_pulse
instead during the power off pulse.

Changes in v5:
* added serdev_device_write_flush() in qca_power_off().
drivers/bluetooth/hci_qca.c | 46 ++++++++++++++++---------------------
1 file changed, 20 insertions(+), 26 deletions(-)

diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
index f036c8f98ea3..681bfa30467e 100644
--- a/drivers/bluetooth/hci_qca.c
+++ b/drivers/bluetooth/hci_qca.c
@@ -60,6 +60,7 @@

nit: Not that it should make a different in normal operation, but 1s
seems extreme. Is there really any chance that the byte hasn't been
sent after say 100ms (which is still an eternity for a single byte)?

/* susclk rate */
#define SUSCLK_RATE_32KHZ 32768
@@ -1013,11 +1014,10 @@ 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;
+ int timeout = __msecs_to_jiffies(POWER_PULSE_TRANS_TIMEOUT_MS);

use msecs_to_jiffies()

[Bala]: will upadte.

/* These power pulses are single byte command which are sent
* at required baudrate to wcn3990. On wcn3990, we have an external
@@ -1029,22 +1029,22 @@ 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 controller", cmd);

+ serdev_device_write_flush(hu->serdev);
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", 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);
- /* Wait for 100 uS for SoC to settle down */
- usleep_range(100, 200);
+ serdev_device_wait_until_sent(hu->serdev, timeout);
+ /* Wait of 5ms is required for assuring to send the byte on the Tx
+ * line and also for the controller to settle down for the received
+ * byte.
+ */
+ usleep_range(5000, 6000);

I incorrectly claimed that there might be still bytes sitting in the
UART FIFO when serdev_device_wait_until_sent() returns, Johan
corrected me on that (thanks!). So if it takes the SoC 100us to settle
down we should be good with the original code.

[Bala]: sure will revert, i think he commented that wait_until_sent()
will only guarantee circular buffer is empty. if wait_until_sent()
guarantee us that the data was transmitted from the FIFO, then 100us will work.