[U-Boot] [PATCH v2 1/4] ns16550: Add function to drain serial output

[Simon Glass]

Hi Wolfgang,

On Sat, Mar 10, 2012 at 12:24 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Simon Glass,
>
> In message <CAPnjgZ3wprPDNUbe0fGbsequXJgQ_bwzkDEu6FeuR-8GG1ndQQ at mail.gmail.com> you wrote:
>>
>> > Also I do not understand why it would be needed at all. =A0We did not
>> > have such a requirement for any system before, so I feel you must be
>> > doing something wrong, or at least very exotic.
>>
>> I put a fully explanation in the previous patch. Let me just add here
>
> Explanations in some other patch are not available when someone reads
> the commit message ...

I did put a motivation in this patch at least:

Sometimes we want to be sure that the output FIFO has fully drained (e.g.
because we are about to reset or the port or reset the board). Add a
function for this.


>
>> that I see a 100ms delay in the reset code to allow serial output to
>> flush, so there is at least in practice a need for this sort of thing.
>
> Note that such a delay is hardware independent.  You implement a
> special solution that works only for a minority of boards.

True, and we could just have the board panic function implement a
delay, particularly if we move to the panic idea and away from putc().

>
>> For most archs the extra code will be removed by the linker.
>
> Ok, granted.
>
>> You may also recall a discussion about a platform where the SPI flash
>> and console uart were muxed, and we had to flush the console uart
>> before switching to SPI. I feel that draining the FIFO could/should be
>> a useful function.
>
> You quote an example of highly specific hardware, which I would not
> hesitate to call a broken design.  I do not really fancy adding code
> to common files for such exceptional situations.

It is certainly broken, yes.

Regards,
Simon

>
> Best regards,
>
> Wolfgang Denk
>
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