On Fri, Apr 20, 2018 at 10:23 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> Hello!
> I note the following in the serial console:
>
> if (is_rproc_serial(vdev)) {
> /*
> * Allocate DMA memory from ancestor. When a virtio
> * device is created by remoteproc, the DMA memory is
> * associated with the grandparent device:
> * vdev => rproc => platform-dev.
> */
> if (!vdev->dev.parent || !vdev->dev.parent->parent)
> goto free_buf;
> buf->dev = vdev->dev.parent->parent;
>
> /* Increase device refcnt to avoid freeing it */
> get_device(buf->dev);
> buf->buf = dma_alloc_coherent(buf->dev, buf_size, &buf->dma,
> GFP_KERNEL);
> }
>
> Added here:
> commit 1b6370463e88b0c1c317de16d7b962acc1dab4f2
> Author: Sjur Brændeland <sjur.brandeland@xxxxxxxxxxxxxx>
> Date: Fri Dec 14 14:40:51 2012 +1030
>
> virtio_console: Add support for remoteproc serial
>
>
> I am not familiar with rproc so I have a question:
> why is it required to use coherent memory here,
> and why through a grandparent device?
I faced similar issue when I tried VirtIO RPMSG bus over
VirtIO MMIO transport.
Here's my fix for VirtIO RPMSG bus driver:
https://patchwork.kernel.org/patch/10155145/
Regards,
Anup
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