[Mesa-dev] DMA_BUF render targets disabled for intel

[Axel Davy]

Hi,

you may be interesting look at this related bug report:
https://bugs.freedesktop.org/show_bug.cgi?id=87452#c5

Yours,

Axel Davy

On 02/04/2015 11:58, Volker Vogelhuber wrote :
> We currently want to stream OpenGL output to an FPGA that does not 
> provide
> a SG controller and should manage the transfers from the CPU memory to 
> it's
> own hardware. For that reason we want to have the OpenGL driver (intel 
> baytrail)
> to render at a specific memory area within the CPU system. Render to 
> texture as
> it is possible e.g. on the PowerVR 530 seems not to be possible, as
> GL_TEXTURE_EXTERNAL_OES is not valid for glFrameBufferTexture2D and
> in contrast to the PowerVR OpenGL implementation, Mesa seems to 
> prohibit the
> use of GL_TEXTURE_2D for textures created by glEGLImageTargetTexture2DOES
> (there is a check within Mesa where glEGLImageTargetTexture2DOES's 
> target has
> to be equal to the target of the texture => GL_TEXTURE_EXTERNAL_OES != 
> GL_TEXTURE_2D).
>
> So the only possible way to render to an EGLImage with memory 
> allocated by myself
> seems to be the use of glEGLImageTargetRenderbufferStorageOES and bind 
> this
> render buffer using glFramebufferRenderbuffer to the FBO.
>
> But for some reason, it seems to be forbidden to use an EGLImage 
> imported from
> a dmabuf as render buffer. At least within 
> src/mesa/drivers/dri/i965/intel_fbo.c there
> is a check:
>
> /* Buffers originating from outside are for read-only. */
>    if (image->dma_buf_imported) {
>       _mesa_error(ctx, GL_INVALID_OPERATION,
>             "glEGLImageTargetRenderbufferStorage(dma buffers are 
> read-only)");
>      return;
> }
>
> This prevents me from doing what I wanted to do and I googled a bit.
> I found someone else that just removed that check:
>
> https://github.com/kalyankondapally/Chromium-OzoneGBM/blob/master/0010-i965-remove-read-only-restriction-of-imported-buffer.patch 
>
>
> and after I did so myself, it just worked as I wanted it to work. I 
> only wonder why this
> limitation has been added. Is it just for some pedantic reasons or is 
> there any good reason
> why EGLImages imported from dmabuf descriptors shouldn't be used for 
> render targets?
>
> -- 
>      Volker
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev