| Message ID | 20200701211337.3027448-1-danielwinkler@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Revert "serial: 8250: Fix max baud limit in generic 8250 port" | expand |
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 >
On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote: > 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) 8250_bcm2835aux.c seems to suffer from a similar issue and solves it like this in the ->probe hook: /* the HW-clock divider for bcm2835aux is 8, * but 8250 expects a divider of 16, * so we have to multiply the actual clock by 2 * to get identical baudrates. */ up.port.uartclk = clk_get_rate(data->clk) * 2; > 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. That sound preferable as adding new quirks into core code feels like a case of midlayer fallacy: https://blog.ffwll.ch/2016/12/midlayers-once-more-with-feeling.html Thanks, Lukas
On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote: > 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. Sounds like a sane fix, thanks for looking into this. greg k-h
On Thu, Jul 02, 2020 at 06:11:52AM +0200, Lukas Wunner wrote: > On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote: > > 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) > > 8250_bcm2835aux.c seems to suffer from a similar issue and > solves it like this in the ->probe hook: > > /* the HW-clock divider for bcm2835aux is 8, > * but 8250 expects a divider of 16, > * so we have to multiply the actual clock by 2 > * to get identical baudrates. > */ > up.port.uartclk = clk_get_rate(data->clk) * 2; 8250_mid for example lies about UART clock due to this. It has a comment in the code in its ->set_termios(). Yes, we have a lot of possibilities here to fix, I guess. We have custom termios callback, also get and set divisor and so on.