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

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Message-Id: <47354634-CA37-47E3-99D2-D4DDB08A9870@suse.de>
Date:	Thu, 18 Apr 2013 10:44:32 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC] arm64: Early printk support for virtio-mmio console devices.



Am 18.04.2013 um 09:32 schrieb Pranavkumar Sawargaonkar <pranavkumar@...aro.org>:

> 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.

A boot loader should easily be able to implement virtio-console for real.

In fact, you should be able to do a simple virtio-console implementation for early printk too, that polls the host for acks rather than use interrupts. Check out my s390-zipl code for reference. I use that there.

The advantage to that would be that no host changes are required whatsoever and the interface strictly stays as it is.


Alex

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