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

[Angus Ainslie]

Hi Heiko,

On 2022-03-17 05:41, 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.thi...@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.ha...@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)) {
+               struct clk clk;
+               if(!clk_get_by_name(dev, "ipg", &clk))
+                       rate = clk_get_rate(&clk);

Is the "ipg" clock the correct name for all of the imx DM boards ?

+       }
+
+       /* as fallback we try to get the clk rate that way */
+       if (rate == 0)
+               rate = imx_get_uartclk();

Would it be better to re-write imx_get_uartclk so that both the getting 
and setting of clocks was correct ?

With DM clocks enabled I don't even think it makes sense to call those 
older functions.

Angus

-       _mxc_serial_setbrg(plat->reg, clk, baudrate, plat->use_dte);
+       _mxc_serial_setbrg(plat->reg, rate, baudrate, plat->use_dte);

        return 0;
 }