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

From: Ohad Ben-Cohen
Date: Wed Jun 22 2011 - 06:47:07 EST

On Wed, Jun 22, 2011 at 5:42 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> On Tue, 21 Jun 2011 10:18:33 +0300, Ohad Ben-Cohen <ohad@xxxxxxxxxx> 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!

And we really liked it: virtio_rpmsg_bus.c, the virtio driver which
does most of the magic here ended up pretty small thanks to virtio.
and the performance numbers are really good, too.

>> +     /* 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.

Yes, I was (mis-)using the config space for now to talk with
platform-specific code (on the host), and not with the peer, so I
opted for simplicity.

But this is definitely one thing that is going away: I don't see any
reason why not just use dma_alloc_coherent (or even dma_pool_create)
directly from the driver here in order to get those buffers.

>> +#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...

Yes, looks like I can remove this. thanks.

>> +#define VIRTIO_ID_RPMSG              10 /* virtio remote processor messaging */
> I think you want 6.  Plan 9 jumped ahead to grab 9 :)

6 it is :)

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