Re: [PATCH 05/10] xen/arm: vpl011: Allocate a new PFN in the toolstack for the virtual console

From: Julien Grall <julien.grall@arm.com>
To: Bhupinder Thakur <bhupinder.thakur@linaro.org>
Cc: xen-devel@lists.xenproject.org,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>
Subject: Re: [PATCH 05/10] xen/arm: vpl011: Allocate a new PFN in the toolstack for the virtual console
Date: Wed, 19 Apr 2017 14:35:01 +0100	[thread overview]
Message-ID: <7da02bd5-151d-8137-e77d-5ede63f2da0b@arm.com> (raw)
In-Reply-To: <CACtJ1JT4y6S3tGsnCLteSYHzDNJ=YBM9RaJrQsx_fxk-MqQSoQ@mail.gmail.com>

On 19/04/17 14:05, Bhupinder Thakur wrote:
> Hi,

Hi Bhupinder,

> On 19 April 2017 at 16:31, Julien Grall <julien.grall@arm.com> wrote:
>> There were some concerns on the first version about using HVM params because
>> this is tying the virtual UART to HVM and only allow us to have one virtual
>> console.
>>
>> HVM params are part of the stable ABI, so this would restrict ourselves to
>> future extension.
>>
>> It was suggested to look at the DOMCTL way, I would have expected to some
>> investigation and a summary in the cover letter. So why do we keep HVM
>> PARAM?
>
> It is more flexible to use DOMCTL interface in terms of supporting
> multiple vUARTs in future without changing the interface. This DOMCTL
> interface cannot be called from xenconsoled though because xenconsoled
> does not know the PFN to be passed to Xen. It is ok to call this
> DOMCTL interface from the toolstack since it knows the PFN and can
> pass it on to Xen.

I am not sure to understand what you mean. The DOMCTL could be used to 
set the PFN by the toolstack and then retrieved by the console.

You could also use xenstore to pass the PFN. So what is the problem?

Cheers,

-- 
Julien Grall

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