[U-Boot] [PATCH v2] NS16550: buffer reads

[Simon Glass]

Hi Graeme,

On Tue, Oct 25, 2011 at 4:37 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
> Hi Simon,
>
> On Wed, Oct 26, 2011 at 10:17 AM, Simon Glass <sjg at chromium.org> wrote:
>
> [big snip]
>
>> Did I mention a can of worms? After 65 messages on this topic Scott's
>> patch seems pretty appealing right now! We can even move it up a level
>> in the s/w stack if that helps.
>
> But I agree with Wolfgang that Scott's proposal only hides the real
> problem even deeper and will make a real solution more difficult
> next time around

I feel that the 'real' solution is flow control or buffering and probably both.

>
>> But to continue this a little, and donning my asbestos suit, should
>> U-Boot have a CONFIG to enable an event loop called in delay
>> functions, network functions, read/write operations, etc.? It would
>> permit us to solve this problem properly I think, if we think it is
>> worth solving. Not saying it is a good idea...
>
> That is what the watchdog code does - It is a horrible hack, and every now
> and again, another patch comes through which adds another call to the
> watchdog trigger in some obscure loop in some obscure code location. Or
> someone submits new code for a board that does not have a watchdog that
> somebody else then uses on a board that does have one and the watchdog
> suddenly triggers resetting the board. It's messy and ugly.
>
> My biggest point about the 'dropped character' issue is that the fix is
> simple provided the 'tasks' that use the serial console behave and inform
> the serial console driver that they have finished receiving characters -
> not a big ask in my opinion. Way smaller that spattering 'Check the
> serial port' all over the code

I kind-of agree so long as it is more of an event loop and less of
something specific to serial (of course serial might be the only
customer but then we could display a spinning thing on the LCD...).
Funnily enough that problem (one bit of code wanting to tell serial
something) exists on Seaboard, where the SPI driver has to tell the
UART to flush or invalidate since they cannot co-exist. And that is
why I was so interested in this patch.

Regards,
Simon

>
> Regards,
>
> Graeme
>