[PATCH 1/3] drm: Wait on the reservation object when sync'ing dmabufs

[Daniel Vetter]

On Sat, Jun 18, 2016 at 04:20:47PM +0100, Chris Wilson wrote:
> Rendering operations to the dma-buf are tracked implicitly via the
> reservation_object (dmabuf->resv). The dmabuf sync ioctl allows
> userspace to wait upon outstanding rendering and prepare the object for
> CPU access (provided by the prime dma_buf_ops.begin_cpu_access). Fill
> this out for the generic drm_gem_prime by waiting on outstanding
> rendering via dmabuf->resv. (This offers an alternative to using poll
> that is consistent with other drivers that may need to more work to
> prepare the object for access by the CPU.)
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/drm_prime.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 780589b420a4..479ff7cc3634 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -28,6 +28,7 @@
>  
>  #include <linux/export.h>
>  #include <linux/dma-buf.h>
> +#include <linux/reservation.h>
>  #include <drm/drmP.h>
>  #include <drm/drm_gem.h>
>  
> @@ -288,6 +289,22 @@ static int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf,
>  	return dev->driver->gem_prime_mmap(obj, vma);
>  }
>  
> +static int drm_gem_begin_cpu_access(struct dma_buf *dma_buf,
> +				    enum dma_data_direction direction)
> +{
> +	bool write = (direction == DMA_BIDIRECTIONAL ||
> +		      direction == DMA_TO_DEVICE);
> +	struct reservation_object *resv = dma_buf->resv;
> +	long ret;
> +
> +	ret = reservation_object_wait_timeout_rcu(resv, write, true,
> +						  MAX_SCHEDULE_TIMEOUT);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}

Maybe we even want this in the dma-buf layer as default function if
nothing else is provided? After all this one here is entirely generic, and
uses neither gem nor even drm_prime knowledge. Either way:

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> +
>  static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
>  	.attach = drm_gem_map_attach,
>  	.detach = drm_gem_map_detach,
> @@ -301,6 +318,7 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
>  	.mmap = drm_gem_dmabuf_mmap,
>  	.vmap = drm_gem_dmabuf_vmap,
>  	.vunmap = drm_gem_dmabuf_vunmap,
> +	.begin_cpu_access = drm_gem_begin_cpu_access,
>  };
>  
>  /**
> -- 
> 2.8.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch