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

[Scott Wood]

On 10/25/2011 06:37 PM, Graeme Russ 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

Even in Linux you can get loss if you overflow the kernel's buffer.

Flow control is just not that commonly used in this sort of application.
 If we insist on software flow control for U-Boot to get any usable
multi-line pasting to work, the user has to reconfigure their terminal
software for this -- it would take some effort for me to figure out how
to do that on our board farm serial server.  And maybe that's not the
right setting for what the user wants to do with the port later on.

Someone also raised the issue of TX buffering -- and you replied that it
should be turned off if hardware flow control is not used.  This is not
what happens in Linux, at least, and we should not be depending in
U-Boot on the other end not using TX buffers.

The point here is to make an incremental improvement that solves a
problem for some people (even if not "solving" the general problem),
without significant impact elsewhere.  The minor size increase when the
option is not enabled can be fixed.  See previous discussion:

http://lists.denx.de/pipermail/u-boot/2011-April/089878.html

If someone wants to further improve things by adding optional interrupt
support or flow control, I don't see how this patch makes that more
difficult.

-Scott