[PATCH][RFC] 8250_dw: unregister dw8250_set_termios for rk3188 chip

[Heiko Stübner]

Am Montag, 20. November 2017, 16:26:56 CET schrieb Ed Blake:
> On 20/11/17 16:14, Shuyu Wei wrote:
> > On Mon, Nov 20, 2017 at 03:44:13PM +0000, Ed Blake wrote:
> >> On 20/11/17 14:40, Shuyu Wei wrote:
> >>> dw8250_set_termios is causing problems for rk3188 on my radxa board.
> >>> It's using a fixed clock at 24M, not baud*16 in dw8250_set_termios.
> >>> I'm not sure if other rk3xxx chips are facing the same problem.
> >>> 
> >>> Signed-off-by Wei Shuyu <wsy at dogben.com>
> >>> ---
> >>> 
> >>>  drivers/tty/serial/8250/8250_dw.c | 3 +++
> >>>  1 file changed, 3 insertions(+)
> >>> 
> >>> diff --git a/drivers/tty/serial/8250/8250_dw.c
> >>> b/drivers/tty/serial/8250/8250_dw.c index 5bb0c42c88dd..e760a5c1f3f6
> >>> 100644
> >>> --- a/drivers/tty/serial/8250/8250_dw.c
> >>> +++ b/drivers/tty/serial/8250/8250_dw.c
> >>> @@ -340,6 +340,9 @@ static void dw8250_quirks(struct uart_port *p,
> >>> struct dw8250_data *data)>>> 
> >>>  			data->skip_autocfg = true;
> >>>  		
> >>>  		}
> >>>  
> >>>  #endif
> >>> 
> >>> +		if (of_device_is_compatible(np, "rockchip,rk3188-uart")) {
> >>> +			p->set_termios = NULL;
> >>> +		}
> >>> 
> >>>  		if (of_device_is_big_endian(p->dev->of_node)) {
> >>>  		
> >>>  			p->iotype = UPIO_MEM32BE;
> >>>  			p->serial_in = dw8250_serial_in32be;
> >> 
> >> Can you provide more details on the problem you're trying to solve?
> > 
> > Hi Ed,
> > 
> > Current dw8250_set_termios() trys to set p->uartclk and d->clk to
> > baud*16, which is incorrect for rk3188. It should be a fixed 24000000.
> > The incorrect value will result in a wrong baud rate, generating bad
> > bytes on my serial console. Heikki Krogerus had worried about this,
> > see https://patchwork.kernel.org/patch/9306275/.
> 
> If the clock is fixed to 24000000, shouldn't clk_round_rate() always
> return that value?  In which case dw8250_set_termios() wouldn't try to
> change the rate.
> 
> If clk_round_rate() is returning a different value for a fixed clock, it
> sounds like it's the clock driver which needs to change.

Also, the rk3188 uarts are definitly not fixed at 24MHz and can use other 
sources as well. So I'm puzzled because at least the serial console on my 
rk3188 radxarock works without issues.

Can you tell us which uart you are failing to control correctly?


I do remember that I ran into problems when the set_termios change
was introduced originally, resulting in the patch
	"serial: 8250_dw: Honor clk_round_rate errors in dw8250_set_termios" [0]
but that is in mainline for quite some time now.

[0] https://patchwork.kernel.org/patch/9594657/


Heiko