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Re: [Xen-devel] [PATCH 00/17 v5] SBSA UART emulation support in Xen





On 05/07/2017 21:05, Stefano Stabellini wrote:
On Wed, 5 Jul 2017, Julien Grall wrote:
On 05/07/2017 20:06, Stefano Stabellini wrote:
On Wed, 5 Jul 2017, Julien Grall wrote:
On 07/04/2017 08:31 AM, Bhupinder Thakur wrote:
Hi Julien,

Hi Bhupinder,

Thank you for the summary!

[...]

Currently, UEFI firmware uses hvc as the console for input/output. Now
with the support
of SBSA UART in Xen, it is preferrable that UEFI firmware should be
able to the uart
as well.

One option which was discussed was to use pl011 purely as a debug
port. Currently the debug
prints are intermixed with the normal console output. Now with uart
port becoming available
the debug prints can be redirected to pl011 thus cleaning up the console
output.

Other option is to output everything on both HVC and pl011 both but it
takes away the advantage
of separating out the debug and normal console prints. However, pl011
can be used as debug
port based on a compile time flag. If this compile-time is off, then
the output can be sent to both
HVC and pl011.

Based on this discussion I feel that:
- the default behaviour should be writing the output to both HVC and
pl011.

Hmmm. If I remember correctly this was suggested but ruled out. It was
considered that pl011 and PV console should not be treated equal. PL011
would
be used for boot diagnostics (i.e imagine an Image with no Xen support).

Actually I remember the opposite:
afd2e931-706b-6e25-1f0e-feee16e83c88@xxxxxxxxxx (this was a private
reply though).

This was an answer to my question whether a user could select the serial by
himself. To this reply, you asked whether it was feasible to output on all the
serials console, but I don't see any yes/no answer.

On the rest of the thread, it has been mentioned it was difficult to multiplex
to serial console (I forwarded you the thread). Christoffer, Laszlo and Ard
agreed that PL011 should only be used as boot diagnostics and debug (if
selected at compile time).

I see now that I missed an important part of the thread. Just follow
Lazlo's suggestion.

Sorry for that. I forgot to include you from beginning.

Cheers,

--
Julien Grall

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