Re: [PATCH v1] drm/tegra: Fix vmapping of prime buffers

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

On 6/29/22 01:42, Dmitry Osipenko wrote:
> The code assumes that Tegra GEM is permanently vmapped, which is not
> true for the scattered buffers. After converting Tegra video decoder
> driver to V4L API, we're now getting a BUG_ON from dma-buf core on playing
> video using libvdpau-tegra on T30+ because tegra_gem_prime_vmap() sets
> vaddr to NULL. Older pre-V4L video decoder driver wasn't vmapping dma-bufs.
> Fix it by actually vmapping the exported GEMs.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>  drivers/gpu/drm/tegra/gem.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 7c7dd84e6db8..81991090adcc 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -704,14 +704,23 @@ static int tegra_gem_prime_vmap(struct dma_buf *buf, struct iosys_map *map)
>  {
>  	struct drm_gem_object *gem = buf->priv;
>  	struct tegra_bo *bo = to_tegra_bo(gem);
> +	void *vaddr;
>  
> -	iosys_map_set_vaddr(map, bo->vaddr);
> +	vaddr = tegra_bo_mmap(&bo->base);
> +	if (IS_ERR(vaddr))
> +		return PTR_ERR(vaddr);
> +
> +	iosys_map_set_vaddr(map, vaddr);
>  
>  	return 0;
>  }
>  
>  static void tegra_gem_prime_vunmap(struct dma_buf *buf, struct iosys_map *map)
>  {
> +	struct drm_gem_object *gem = buf->priv;
> +	struct tegra_bo *bo = to_tegra_bo(gem);
> +
> +	tegra_bo_munmap(&bo->base, map->vaddr);
>  }
>  
>  static const struct dma_buf_ops tegra_gem_prime_dmabuf_ops = {

BTW, previously I only tested video dec on T30 using the grate-driver
kernel that properly vmaps GEMs. That's why it wasn't caught earlier.

-- 
Best regards,
Dmitry