linux-kernel - Re: [PATCH v3] virtio: Add platform bus driver for memory mapped virtio device

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Message-ID: <87lisjq6tu.fsf@rustcorp.com.au>
Date:	Tue, 18 Oct 2011 14:39:17 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Pawel Moll <pawel.moll@....com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	virtualization@...ts.linux-foundation.org
Cc:	Anthony Liguori <aliguori@...ibm.com>,
	"Michael S.Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3] virtio: Add platform bus driver for memory mapped virtio device

On Thu, 06 Oct 2011 18:13:50 +0100, Pawel Moll <pawel.moll@....com> wrote:
> > I'll post the updated device spec shortly.
> 
> Here it goes. I'm actually happy about the "maximum queue size" solution
> - it worked out quite neat in the end :-)
> 
> Please, do have a look at the hopefully final shape of things and
> comment if you still see some potential issues :-)
> 
> Cheers!
> 
> Pawel

Looks good.  I'll have a go at moving it across to the LyX master soon.

> \item 0x028 | W | GuestPageSize \\
> Guest page size.\\
> Device driver must write the guest page size in bytes to the register
> during initialization, before any queues are used.

This has to be a power of 2, and you should specify what it's used for.
It's really the multiplier for PFN values, right?

> \item 0x03c | W | QueueAlign \\
> Used Ring alignment in the virtual queue.\\
> Writing to this register notifies the Host about alignment boundary of
> the Used Ring in bytes. This applies to the queue selected by writing to
> QueueSel.

Either specify that this must be a power of 2, or actually specify it as
the power of 2 to use, (ie. valid values are 1 through 16, with 12 being
the value that virtio PCI would use).

Otherwise you have to do a divide on the qemu side.

Looks good otherwise though!

Cheers,
Rusty.
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