linux-kernel - RE: [PATCHv2] virtio_console: Add support for remoteproc serial

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Date:	Thu, 20 Sep 2012 11:29:27 +0200
From:	Sjur BRENDELAND <sjur.brandeland@...ricsson.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Sjur Brændeland <sjurbren@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Amit Shah <amit.shah@...hat.com>
Subject: RE: [PATCHv2] virtio_console: Add support for remoteproc serial

> From: Michael S. Tsirkin [mailto:mst@...hat.com]
> sjur.brandeland@...ricsson.com wrote:
> > From: Sjur Brændeland <sjur.brandeland@...ricsson.com>
> >
> > Add a simple serial connection driver called
> > VIRTIO_ID_RPROC_SERIAL (0xB) for communicating with a
> > remote processor in an asymmetric multi-processing
> > configuration.
> >
> > This implementation reuses the existing virtio_console
> > implementation, and adds support for DMA allocation
> > of data buffers and disables use of tty console and
> > the virtio control queue.
> 
> Can't repoteproc work with control queue?
> Reason I ask, there are known races when
> using config space and I was working on
> a spec change that uses control queue for
> all config accesses.

In my case rproc-serial will be used for transferring boot
image or crash-dump to a modem. In these scenarios the
execution environment is very limited (no OS) and  the size
and complexity of the virtio code at the modem should be kept
to a minimum.

The usage pattern in this case is also very simple,
the virtio device is opened only once, and only reopened
after a complete modem cold-start.

So the control queue is not appropriate for my use-case,
simplicity is the most important requirement.
(And currently the virtio config-space is not supported
by remoteproc anyway).

I don't know if other potential users of rproc_serial have more
complex use-cases in mind?

Regards,
Sjur



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