[Intel-gfx] [PATCH] drm/i915: Support to create uncached user mapping for a Gem object

[Chris Wilson]

On Thu, Oct 23, 2014 at 04:03:56PM +0530, akash.goel at intel.com wrote:
>  drivers/gpu/drm/i915/i915_dma.c |  3 +++
>  drivers/gpu/drm/i915/i915_gem.c | 17 +++++++++++++++++
>  include/uapi/drm/i915_drm.h     |  4 ++++
>  3 files changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 1b39807..2d8191a 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1027,6 +1027,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
>  	case I915_PARAM_CMD_PARSER_VERSION:
>  		value = i915_cmd_parser_get_version();
>  		break;
> +	case I915_PARAM_HAS_UC_MMAP:
> +		value = 1;
> +		break;
>  	default:
>  		DRM_DEBUG("Unknown parameter %d\n", param->param);
>  		return -EINVAL;
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 1b192d4..16b267b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1492,6 +1492,23 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>  	addr = vm_mmap(obj->filp, 0, args->size,
>  		       PROT_READ | PROT_WRITE, MAP_SHARED,
>  		       args->offset);

Forgot to mutter about:

if (args->flags & INVALID_FLAGS)
	return -EINVAL;

and the param then makes better sense as
I915_PARAM_HAS_EXT_MMAP (extended mmap interface, which we can then
version)

In future we can test for EXT_MMAP support and
mmap(RANDOM_FLAG) returning EINVAL for any new extension
flags.

> +
> +	if (args->flags & I915_GEM_USE_UNCACHED_MMAP) {
> +		struct mm_struct *mm = current->mm;
> +		struct vm_area_struct *vma;
> +		down_write(&mm->mmap_sem);
> +		vma = find_vma(mm, addr);
> +		if (!vma) {
> +			drm_gem_object_unreference_unlocked(obj);
> +			return -EINVAL;
> +		}
> +		/* Change the page attribute to uncached (along with
> +		 * write-combinning to get better performance) */
> +		vma->vm_page_prot =
> +			pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> +		up_write(&mm->mmap_sem);
> +	}
> +
>  	drm_gem_object_unreference_unlocked(obj);
>  	if (IS_ERR((void *)addr))
>  		return addr;
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index ff57f07..3d0b1c0 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -340,6 +340,7 @@ typedef struct drm_i915_irq_wait {
>  #define I915_PARAM_HAS_EXEC_HANDLE_LUT   26
>  #define I915_PARAM_HAS_WT     	 	 27
>  #define I915_PARAM_CMD_PARSER_VERSION	 28
> +#define I915_PARAM_HAS_UC_MMAP  	 29
>  
>  typedef struct drm_i915_getparam {
>  	int param;
> @@ -487,6 +488,9 @@ struct drm_i915_gem_mmap {
>  	 * This is a fixed-size type for 32/64 compatibility.
>  	 */
>  	__u64 addr_ptr;
> +
> +#define I915_GEM_USE_UNCACHED_MMAP (1<<0)

#define I915_MMAP_WC is shorter
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre