linux-kernel - Re: [Xen-devel] [PATCH] xen: use hvc console for dom0

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Message-ID: <19afb9f9-a845-e627-8f78-d1fdb349c6bd@arm.com>
Date:   Tue, 27 Feb 2018 20:09:05 +0000
From:   Julien Grall <julien.grall@....com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     nd@....com, Juergen Gross <jgross@...e.com>,
        Andrii Anisov <andrii_anisov@...m.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        boris.ostrovsky@...cle.com, jbeulich@...e.com
Subject: Re: [Xen-devel] [PATCH] xen: use hvc console for dom0

Hi,

On 27/02/2018 20:03, Stefano Stabellini wrote:
> On Tue, 27 Feb 2018, Julien Grall wrote:
>> Hi,
>>
>> On 26/02/18 12:32, Juergen Gross wrote:
>>> On 26/02/18 13:06, Andrii Anisov wrote:
>>>> Hello Juergen,
>>>>
>>>>
>>>> On 26.02.18 13:08, Juergen Gross wrote:
>>>>> Today the hvc console is added as a preferred console for pv domUs
>>>>> only. As this requires a boot parameter for getting dom0 messages per
>>>>> default add it for dom0, too.
>>>>>
>>>>> Signed-off-by: Juergen Gross <jgross@...e.com>
>>>>> ---
>>>>>     arch/x86/xen/enlighten_pv.c | 4 +++-
>>>>>     1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>>>> Is this something x86 specific? Could it be a generic approach?
>>>
>>> In case ARM wants something similar I guess the test for
>>> xen_initial_domain() should be dropped in xen_early_init().
>> I am pretty sure we discussed to remove !xen_initial_domain() for Arm in the
>> past. But I don't remember why the patch was not sent to remove it.
>>
>> Anyway, I guess this should be fine to have hvc as a preferred console for the
>> initial domain as well.
> 
> Usually, Dom0 has access to several physical UARTs and/or VGA, making
> this patch less obviously desirable. I think that for Dom0 the best
> behavior would be to add "hvc0" as first console rather than last
> console, so that if the user specified something else, this call won't
> interfere with it.

Well, that's exactly the goal of add_preferred_console. It will use hvc0 
unless specified otherwise by the user on the command line.

Cheers,

-- 
Julien Grall