linux-kernel - Re: [RFC 7/8] drivers: introduce rpmsg, a remote-processor messaging bus

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Message-ID: <87liwu8u3q.fsf@rustcorp.com.au>
Date:	Wed, 22 Jun 2011 12:12:33 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ohad Ben-Cohen <ohad@...ery.com>, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:	akpm@...ux-foundation.org, Brian Swetland <swetland@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...retlab.ca>,
	davinci-linux-open-source 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: [RFC 7/8] drivers: introduce rpmsg, a remote-processor messaging bus

On Tue, 21 Jun 2011 10:18:33 +0300, Ohad Ben-Cohen <ohad@...ery.com> wrote:
> Add a virtio-based IPC bus, which enables kernel users to communicate
> with remote processors over shared memory using a simple messaging
> protocol.

Wow, sometimes one writes a standard and people use it.  Thanks!

I'm still digesting exactly what you're doing, but this is a bit
unconventional:

> +	/* Platform must supply pre-allocated uncached buffers for now */
> +	vdev->config->get(vdev, VPROC_BUF_ADDR, &addr, sizeof(addr));
> +	vdev->config->get(vdev, VPROC_BUF_NUM, &num_bufs, sizeof(num_bufs));
> +	vdev->config->get(vdev, VPROC_BUF_SZ, &buf_size, sizeof(buf_size));
> +	vdev->config->get(vdev, VPROC_BUF_PADDR, &vrp->phys_base,
> +						sizeof(vrp->phys_base));

The normal way is to think of the config space as a structure, and use
offsets rather than using an enum value to distinguish the fields.

> +#define RPMSG_NAME_SIZE			32
> +#define RPMSG_DEVICE_MODALIAS_FMT	"rpmsg:%s"
> +
> +struct rpmsg_device_id {
> +	char name[RPMSG_NAME_SIZE];
> +	kernel_ulong_t driver_data	/* Data private to the driver */
> +			__attribute__((aligned(sizeof(kernel_ulong_t))));
> +};

This alignment directive seems overkill...

> +#define VIRTIO_ID_RPMSG		10 /* virtio remote processor messaging */

I think you want 6.  Plan 9 jumped ahead to grab 9 :)

Cheers,
Rusty.
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