On Wed, Jul 01, 2020 at 02:13:36PM -0700, Daniel Winkler wrote:
This change regresses the QCA6174A-3 bluetooth chip, preventing firmware from being properly loaded. Without this change, the chip works as intended.
The device is the Kukui Chromebook using the Mediatek chipset and the 8250_mtk uart. Initial controller baudrate is 115200 and operating speed is 3000000. Our entire suite of bluetooth tests now fail on this platform due to an apparent failure to sync its firmware on initialization.
Ok. It's mediatek 8250 driver, which is responsible for the failure. Then we'll have two options:
1) Add a new capability like UART_CAP_NO16DIV and take it into account in the serial8250_get_baud_rate() method.
I don't have a documentation for the Mediatek UART port, but it seems to me that that controller calculates the baud rate differently from the standard 8250 port. A standard 8250 port does that by the next formulae: baud = uartclk / (16 * divisor). While it seems to me that the Mediatek port uses the formulae like: baud = uartclk / divisor. (Please, correct me if I'm wrong) If so, then we could introduce a new capability like UART_CAP_NO16DIV. The 8250_mtk driver will add it to the 8250-port capabilities field. The serial8250_get_baud_rate() method should be altered in a way so one would check whether the UART_CAP_NO16DIV flag is set and if it is then the uart_get_baud_rate() function will be called without uartclk normalized by the factor of 16.
2) Manually call serial8250_do_set_divisor() in the custom set_termios() callback.
Just add the uart_update_timeout() and serial8250_do_set_divisor() methods invocation into the mtk8250_set_termios() function, which the original commit 81bb549fdf14 ("serial: 8250_mtk: support big baud rate") author should have done in the first place.
-Sergey
The driver is in the cros tree at drivers/bluetooth/hci_qca.c and uses the serdev interface. Specifically, this is the QCA_ROME chipset.
Daniel Winkler (1): Revert "serial: 8250: Fix max baud limit in generic 8250 port"
drivers/tty/serial/8250/8250_port.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
-- 2.27.0.212.ge8ba1cc988-goog