From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] EFI development issues
Date: Fri, 17 Jan 2020 09:57:15 +0100 [thread overview]
Message-ID: <149c932d-16b6-f0da-9f7f-1e10cd7e74c5@suse.com> (raw)
In-Reply-To: <9a0fb4ab-831d-f293-7fa1-b969a1571690@citrix.com>
On 16.01.2020 21:28, Andrew Cooper wrote:
> On 13/01/2020 16:46, Jan Beulich wrote:
>> On 13.01.2020 17:02, Andrew Cooper wrote:
>>> (Waiting for a
>>> keypress on StdIn however does work, which is how I eventually diagnosed
>>> that it was an output problem.) Skipping this logic allows debugging to
>>> work.
>> As should then do -basevideo.
>
> That is another observation. It is very confusing having command line
> parameters to xen.efi which are different to command line parameters to
> Xen. The parameters to xen.efi aren't documented anywhere, as far as I
> can tell.
Well, if "xen.efi -help" doesn't count, then yes, this may want adding
to efi.pandoc. The -cfg option is mentioned there (albeit not in a
systematic manner), and the only other possibly useful option that was
there from the beginning was -basevideo; -mapbs appeared only later.
When creating that doc, focus was clearly on the commonly used aspects.
>>> What is the purpose of changing to a different mode? Certainly as far
>>> as serial consoles go, sticking with the mode the loader uses certainly
>>> feels like a safer option.
>> Does a serial console report a "resolution" in the first place?
>
> How would I find out?
You could log the values found in case of a pure serial console
setup (i.e. headless). But the multiplexed case is going to be the
more involved one anyway.
>> And
>> if we were able to (sufficiently easily) tell video from serial
>> console, how would we deal with the case of StdOut / StdErr being
>> multiplexed to both?
>
> In my case they are multiplexed, and all work fine before set_mode() call.
>
> After set_mode(), VGA still works, while serial sees nothing further on
> StdOut/Stderr (pre-existing lines are still in place).
Unfortunately the two of the three EFI boxes I routinely work with
and that I've tried mux-ed configurations on had no such issue, so
I'm afraid I couldn't easily debug this myself even if I wanted to.
But anyway, situations like this one are exactly why -basevideo has
been there from the very beginning.
For systems with a video device, the mode set here may be the mode
an eventual X driver also uses; sadly Linux'es kernel mode setting
looks to be having a high (and increasing) failure rate according
to my experience. Possibly much like the high rate of EFI issues
you observe / get reported, as opposed to me not having seen most
of them on the boxes I work with all the time (i.e. simply bad vs
good luck).
Jan
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next prev parent reply other threads:[~2020-01-17 8:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 16:02 [Xen-devel] EFI development issues Andrew Cooper
2020-01-13 16:46 ` Jan Beulich
2020-01-16 20:28 ` Andrew Cooper
2020-01-17 8:57 ` Jan Beulich [this message]
2020-01-17 15:24 ` Jan Beulich
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