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

[Lukasz Majewski]

Hi Sean,

> 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?
> 
> mx6ull at least does not have CONFIG_SPL_CLK enabled.

The problem with serial is that not all boards support DM clock in SPL.
I'm wondering if this patch has passed the CI tests for all boards.

> 
> > +		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




Best regards,

Lukasz Majewski

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