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

[Julien Grall <julien.grall@xxxxxxx>]

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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