On Mon, Dec 2, 2019 at 5:36 PM Gurchetan Singh
<gurchetansingh@xxxxxxxxxxxx> wrote:
>
> With the misc device, we should end up using the result of
> get_arch_dma_ops(..) or dma-direct ops.
>
> This can allow us to have WC mappings in the guest after
> synchronization.
>
> Signed-off-by: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx>
> ---
> drivers/dma-buf/udmabuf.c | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 0a610e09ae23..61b0a2cff874 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -18,6 +18,7 @@ static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes */
> struct udmabuf {
> pgoff_t pagecount;
> struct page **pages;
> + struct sg_table *sg;
> struct miscdevice *device;
> };
>
> @@ -98,20 +99,58 @@ static void unmap_udmabuf(struct dma_buf_attachment *at,
> static void release_udmabuf(struct dma_buf *buf)
> {
> struct udmabuf *ubuf = buf->priv;
> + struct device *dev = ubuf->device->this_device;
> pgoff_t pg;
>
> + if (ubuf->sg)
> + put_sg_table(dev, ubuf->sg, DMA_BIDIRECTIONAL);
> +
> for (pg = 0; pg < ubuf->pagecount; pg++)
> put_page(ubuf->pages[pg]);
> kfree(ubuf->pages);
> kfree(ubuf);
> }
>
> +static int begin_cpu_udmabuf(struct dma_buf *buf,
> + enum dma_data_direction direction)
> +{
> + struct udmabuf *ubuf = buf->priv;
> + struct device *dev = ubuf->device->this_device;
> +
> + if (!ubuf->sg) {
> + ubuf->sg = get_sg_table(dev, buf, direction);
> + if (IS_ERR(ubuf->sg))
> + return PTR_ERR(ubuf->sg);
> + } else {
> + dma_sync_sg_for_device(dev, ubuf->sg->sgl,
> + ubuf->sg->nents,
> + direction);
I know this solves the issue (flush the CPU cache before WC access),
but it looks like an abuse? It is counter-intuitive that the buffer
is synced for device when one wants CPU access.
> + }
> +
> + return 0;
> +}
> +
> +static int end_cpu_udmabuf(struct dma_buf *buf,
> + enum dma_data_direction direction)
> +{
> + struct udmabuf *ubuf = buf->priv;
> + struct device *dev = ubuf->device->this_device;
> +
> + if (!ubuf->sg)
> + return -EINVAL;
> +
> + dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
> + return 0;
> +}
> +
> static const struct dma_buf_ops udmabuf_ops = {
> .cache_sgt_mapping = true,
> .map_dma_buf = map_udmabuf,
> .unmap_dma_buf = unmap_udmabuf,
> .release = release_udmabuf,
> .mmap = mmap_udmabuf,
> + .begin_cpu_access = begin_cpu_udmabuf,
> + .end_cpu_access = end_cpu_udmabuf,
> };
>
> #define SEALS_WANTED (F_SEAL_SHRINK)
> --
> 2.24.0.393.g34dc348eaf-goog
>
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