Re: [FFmpeg-devel] [PATCH v3] lavu/hwcontext_vaapi: Use vaMapBuffer2 for mapping image buffers

[Mark Thompson <sw@jkqxz.net>]

On 27/10/2023 11:00, David Rosca wrote:
> This allows some optimizations in driver, such as not having to read
> back the data if write-only mapping is requested.
> ---
> v3: Fix another warning
> 
>   libavutil/hwcontext_vaapi.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/libavutil/hwcontext_vaapi.c b/libavutil/hwcontext_vaapi.c
> index 558fed94c6..86b0852c12 100644
> --- a/libavutil/hwcontext_vaapi.c
> +++ b/libavutil/hwcontext_vaapi.c
> @@ -799,6 +799,9 @@ static int vaapi_map_frame(AVHWFramesContext *hwfc,
>       VAStatus vas;
>       void *address = NULL;
>       int err, i;
> +#if VA_CHECK_VERSION(1, 21, 0)
> +    uint32_t vaflags = 0;
> +#endif
>   
>       surface_id = (VASurfaceID)(uintptr_t)src->data[3];
>       av_log(hwfc, AV_LOG_DEBUG, "Map surface %#x.\n", surface_id);
> @@ -882,7 +885,15 @@ static int vaapi_map_frame(AVHWFramesContext *hwfc,
>           }
>       }
>   
> +#if VA_CHECK_VERSION(1, 21, 0)
> +    if (flags & AV_HWFRAME_MAP_READ || !(flags & AV_HWFRAME_MAP_OVERWRITE))
> +        vaflags |= VA_MAPBUFFER_FLAG_READ;

I don't understand where the !overwrite has come from in this condition?

If the user requested write-only but not overwrite then they're expecting to write some pixels within the image (such as adding an overlay), but don't want to read anything.

> +    if (flags & AV_HWFRAME_MAP_WRITE)
> +        vaflags |= VA_MAPBUFFER_FLAG_WRITE;
> +    vas = vaMapBuffer2(hwctx->display, map->image.buf, &address, vaflags);
> +#else
>       vas = vaMapBuffer(hwctx->display, map->image.buf, &address);
> +#endif
>       if (vas != VA_STATUS_SUCCESS) {
>           av_log(hwfc, AV_LOG_ERROR, "Failed to map image from surface "
>                  "%#x: %d (%s).\n", surface_id, vas, vaErrorStr(vas));

Please add a note that there is a compatibility layer in libva so that MapBuffer2 calls MapBuffer if the driver doesn't expose it directly, so this does work with older drivers.  (The patch looked wrong before I realised that.)

Thanks,

- Mark
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