[U-Boot] [PATCH v2 09/11] drivers: serial_sifive: Skip baudrate config if no input clock

[Auer, Lukas <lukas.auer@aisec.fraunhofer.de>]

On Sun, 2019-01-20 at 17:07 -0800, Atish Patra wrote:
> On 1/20/19 12:22 PM, Auer, Lukas wrote:
> > Hi Anup,
> > 
> > On Fri, 2019-01-18 at 11:19 +0000, Anup Patel wrote:
> > > From: Atish Patra <atish.patra@wdc.com>
> > > 
> > > It is possible that input clock is not available because clk
> > > device was not available and 'clock-frequency' DT property is
> > > also not available.
> > 
> > Why would the clock device not be available?
> > I suspect the problem is that the clock driver is not probed pre-
> > relocation. Adding DM_FLAG_PRE_RELOC to the driver flags would fix
> > this.
> > 
> 
> The problem is serial driver gets probed first before clock driver
> even 
> if we add DM_FLAG_PRE_RELOC.

That makes sense. I just browsed through the code to see what other
boards do here. The serial driver for the MPC83xx SoC series directly
probes the clock driver (see get_serial_clock in
driver/clk/mpc83xx_clk.c called from the serial driver). Maybe we
should do something similar here?

> 
> > > In this case, instead of failing we should just skip baudrate
> > > config by returning zero.
> > 
> > Won't this cause issues if an incorrect baudrate is set?
> > 
> It might be possible that baudrate is configured by earlier boot
> stage.
> Thus, any early information can be displayed in console by the
> serial 
> driver even if it is not configured correctly by u-boot.
> 

Yes, it is very likely not going to be a problem, but if we can fix it
it would be great :)

Thanks,
Lukas

> 
> Regards,
> Atish
> > Thanks,
> > Lukas
> > 
> > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > > Signed-off-by: Anup Patel <anup.patel@wdc.com>
> > > Reviewed-by: Alexander Graf <agraf@suse.de>
> > > ---
> > >   drivers/serial/serial_sifive.c | 32 ++++++++++++++++-----------
> > > -----
> > >   1 file changed, 16 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/drivers/serial/serial_sifive.c
> > > b/drivers/serial/serial_sifive.c
> > > index ea4d35d48c..537bc7a975 100644
> > > --- a/drivers/serial/serial_sifive.c
> > > +++ b/drivers/serial/serial_sifive.c
> > > @@ -99,27 +99,27 @@ static int _sifive_serial_getc(struct
> > > uart_sifive
> > > *regs)
> > >   
> > >   static int sifive_serial_setbrg(struct udevice *dev, int
> > > baudrate)
> > >   {
> > > -	int err;
> > > +	int ret;
> > >   	struct clk clk;
> > >   	struct sifive_uart_platdata *platdata =
> > > dev_get_platdata(dev);
> > > +	u32 clock = 0;
> > >   
> > > -	err = clk_get_by_index(dev, 0, &clk);
> > > -	if (!err) {
> > > -		err = clk_get_rate(&clk);
> > > -		if (!IS_ERR_VALUE(err))
> > > -			platdata->clock = err;
> > > -	} else if (err != -ENOENT && err != -ENODEV && err != -ENOSYS)
> > > {
> > > +	ret = clk_get_by_index(dev, 0, &clk);
> > > +	if (IS_ERR_VALUE(ret)) {
> > >   		debug("SiFive UART failed to get clock\n");
> > > -		return err;
> > > -	}
> > > -
> > > -	if (!platdata->clock)
> > > -		platdata->clock = dev_read_u32_default(dev, "clock-
> > > frequency", 0);
> > > -	if (!platdata->clock) {
> > > -		debug("SiFive UART clock not defined\n");
> > > -		return -EINVAL;
> > > +		ret = dev_read_u32(dev, "clock-frequency", &clock);
> > > +		if (IS_ERR_VALUE(ret)) {
> > > +			debug("SiFive UART clock not defined\n");
> > > +			return 0;
> > > +		}
> > > +	} else {
> > > +		clock = clk_get_rate(&clk);
> > > +		if (IS_ERR_VALUE(clock)) {
> > > +			debug("SiFive UART clock get rate failed\n");
> > > +			return 0;
> > > +		}
> > >   	}
> > > -
> > > +	platdata->clock = clock;
> > >   	_sifive_serial_setbrg(platdata->regs, platdata->clock,
> > > baudrate);
> > >   
> > >   	return 0;