[RFC] serial: mxc: get the clock frequency from the used clock for the device

[Heiko Thiery]

Hi Sean,

Am Do., 17. März 2022 um 15:38 Uhr schrieb Sean Anderson <seanga2 at gmail.com>:
>
> Hi Heiko,
>
> On 3/17/22 8:41 AM, Heiko Thiery wrote:
> > With the clock driver enabled for the imx8mq, it was noticed that the
> > frequency used to calculate the baud rate is always taken from the root
> > clock of UART1. This can cause problems if UART1 is not used as console
> > and the settings are different from UART1. The result is that the console
> > output is garbage. To do this correctly the UART frequency is taken from
> > the used device. For the implementations that don't have the igp clock
> > frequency written or can't return it the old way is tried.
> >
> > Signed-off-by: Heiko Thiery <heiko.thiery at gmail.com>
> > ---
> >   drivers/serial/serial_mxc.c | 15 +++++++++++++--
> >   1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
> > index e4970a169b..6fdb2b2397 100644
> > --- a/drivers/serial/serial_mxc.c
> > +++ b/drivers/serial/serial_mxc.c
> > @@ -3,6 +3,7 @@
> >    * (c) 2007 Sascha Hauer <s.hauer at pengutronix.de>
> >    */
> >
> > +#include <clk.h>
> >   #include <common.h>
> >   #include <dm.h>
> >   #include <errno.h>
> > @@ -266,9 +267,19 @@ __weak struct serial_device *default_serial_console(void)
> >   int mxc_serial_setbrg(struct udevice *dev, int baudrate)
> >   {
> >       struct mxc_serial_plat *plat = dev_get_plat(dev);
> > -     u32 clk = imx_get_uartclk();
> > +     u32 rate = 0;
> > +
> > +     if (IS_ENABLED(CONFIG_CLK)) {
>
> CONFIG_IS_ENABLED?

This should be correct. The CONFIG_IS_ENABLED is a preprocessor macro
and the IS_ENABLED can be used in c code. Or do you mean something
else?

>
> mx6ull at least does not have CONFIG_SPL_CLK enabled.

I expect that in that case it will fallback to the old behavior ... not?

>
> > +             struct clk clk;
> > +             if(!clk_get_by_name(dev, "ipg", &clk))
> > +                     rate = clk_get_rate(&clk);
> > +     }
> > +
> > +     /* as fallback we try to get the clk rate that way */
> > +     if (rate == 0)
>
> !rate || IS_ERR_VALUE(rate)
>
> > +             rate = imx_get_uartclk();
> >
> > -     _mxc_serial_setbrg(plat->reg, clk, baudrate, plat->use_dte);
> > +     _mxc_serial_setbrg(plat->reg, rate, baudrate, plat->use_dte);
> >
> >       return 0;
> >   }
> >
> --Sean

-- 
Heiko