linux-kernel - Re: [RFC] arm64: Early printk support for virtio-mmio console devices.

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Message-ID: <87ehe3bbsm.fsf@rustcorp.com.au>
Date:	Mon, 22 Apr 2013 10:51:13 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
Cc:	"kvmarm\@lists.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	linux-kernel@...r.kernel.org, Anup Patel <anup.patel@...aro.org>
Subject: Re: [RFC] arm64: Early printk support for virtio-mmio console devices.

Pranavkumar Sawargaonkar <pranavkumar@...aro.org> writes:
> On 18 April 2013 12:21, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>
>> PranavkumarSawargaonkar <pranavkumar@...aro.org> writes:
>> > From: Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
>> >
>> > This patch implements early printk support for virtio-mmio console devices without using any hypercalls.
>>
>> This makes some sense, though not sure that early console *read* makes
>> much sense.  I can see the PCI version of this being useful as well.
>
> Read can be useful for "mach-virt" which will have only virtio console
> as a console device. Then if someone wants to have UEFI or any other
> boot-loader emulation, which expects user to input few things, in that
> case read might become handy.

But implementing virtio inside a bootloader has already been done for
coreboot, for example.  A bootloader probably wants a virtio block
device, so a console is trivial.

A single writable field for debugging makes sense.  Anything more is far
less certain.

Thanks,
Rusty.
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