linux-kernel - Re: [PATCH 0/2] Early printk support for virtio console devices.

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Message-ID: <CALrVBkuyby_KY_M+yp0e=PLk=7_W_kSxxm62YYSwwp8rwLsCAQ@mail.gmail.com>
Date:	Fri, 26 Apr 2013 18:29:45 +0530
From:	Anup Patel <anup.patel@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linaro-kernel@...ts.linaro.org,
	Peter Maydell <peter.maydell@...aro.org>, patches@...aro.org,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>, kvmarm@...ts.cs.columbia.edu,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/2] Early printk support for virtio console devices.

On 26 April 2013 18:03, Arnd Bergmann <arnd@...db.de> wrote:
> On Friday 26 April 2013 17:36:16 Anup Patel wrote:
>> On 26 April 2013 17:03, Peter Maydell <peter.maydell@...aro.org> wrote:
>> > On 26 April 2013 12:19, Alexander Graf <agraf@...e.de> wrote:
>> >> MMIO registers are handled by a different layer than the virtio
>> >> console itself. After the virtio refactoring in QEMU, they will
>> >> be completely separate drivers.
>> >
>> > Good point -- we don't really want to be mixing up the
>> > transport and the backend. You can see it in the kvmtool
>> > patch, in fact -- it introduces an "if this is virtio-console"
>> > special case into the mmio.c file which previously was
>> > entirely backend agnostic.
>>
>> Well, we can always have virtio device specific config registers
>> handle by virtio device backends and generic virtio config register
>> handled by transport.
>>
>> kvmtool patch is hacky because it does not provide virtio device
>> specific config read/write callbacks.
>
> Couldn't kvmtool implement the interface used by smh_printch()
> for early output instead?
>
> Or if that's not a fitting inteface, maybe a psci call for writing
> a character to the console?
>
>         Arnd

I am curious about how smh-based or hypercall-based early prints would
be handled in following scenario:

"A board is running KVM ARM enabled kernel and linux console on serial
port. Now a user remotely connects to the board via telnet/ssh and
launches a VM with smh-based or hypercall-based earlyprintk."

In the above scenario, will smh-based or hypercall-based earlyprints
appear to user on remote shell or not ?

--Anup
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