[U-Boot] [PATCH 03/11] serial: atmel_usart: Use fixed clock value in SPL version

[Eugen.Hristev at microchip.com]

On 20.03.2019 09:30, Stefan Roese wrote:
> 
> On 20.03.19 08:25, Eugen.Hristev at microchip.com wrote:
>>
>>
>> On 19.03.2019 17:56, Stefan Roese wrote:
>>> External E-Mail
>>>
>>>
>>> This patch adds an alterative SPL version of atmel_serial_enable_clk().
>>> This enables the usage of this driver without full clock support (in
>>> drivers and DT nodes). This saves some space in the SPL image.
>>>
>>> If some boards need a different clock than the one provided with this
>>> patch, then support for this needs to be added later.
>>>
>>> Signed-off-by: Stefan Roese <sr at denx.de>
>>> Cc: Heiko Schocher <hs at denx.de>
>>> Cc: Andreas Bießmann <andreas at biessmann.org>
>>> Cc: Eugen Hristev <eugen.hristev at microchip.com>
>>> ---
>>>    drivers/serial/atmel_usart.c | 12 ++++++++++++
>>>    1 file changed, 12 insertions(+)
>>>
>>> diff --git a/drivers/serial/atmel_usart.c b/drivers/serial/atmel_usart.c
>>> index aa8cdff840..049172baef 100644
>>> --- a/drivers/serial/atmel_usart.c
>>> +++ b/drivers/serial/atmel_usart.c
>>> @@ -218,6 +218,17 @@ static const struct dm_serial_ops 
>>> atmel_serial_ops = {
>>>        .setbrg = atmel_serial_setbrg,
>>>    };
>>> +#ifdef CONFIG_SPL_BUILD
>>> +static int atmel_serial_enable_clk(struct udevice *dev)
>>> +{
>>> +    struct atmel_serial_priv *priv = dev_get_priv(dev);
>>> +
>>> +    /* Use fixed clock value in SPL */
>>> +    priv->usart_clk_rate = 132096000;
>>
>> Hi Stefan,
>>
>> Does this mean that the SPL will work *if and only if* this clock
>> matches the board's clock, for all at91 boards? (thus, boards having a
>> different clock , the serial will not function correctly anymore ?)
> 
> Yes, thats the case (as explained in the commit message above). For
> this to work on all boards we need to add some macro like
> CONFIG_DEBUG_UART_CLOCK which can be set by each board port
> individually.
> 
> If agreed on such an idea, I can add this new Kconfig option in a
> later version of this patch. Perhaps something like
> CONFIG_SPL_UART_CLOCK?

If this breaks the serial for the other boards... it's not good.
I think either we do a patch that fixes a thing, but does not break 
other functionality... or we leave it as is.
Would hate to see serial failing on all other SPLs

How big is the SPL reduction with this ?
Maybe just keep old code in case CONFIG_SPL_UART_CLOCK is *not* defined ?
and if defined, use the hardcoded value from config ?

Eugen
> 
> Thanks,
> Stefan