[Intel-gfx] [PATCH 4/4] drm/i915: Support for pread/pwrite from/to non shmem backed objects

[Chris Wilson]

On Wed, Jul 22, 2015 at 07:21:49PM +0530, ankitprasad.r.sharma at intel.com wrote:
>  static int
>  i915_gem_shmem_pread(struct drm_device *dev,
>  		     struct drm_i915_gem_object *obj,
> @@ -754,17 +850,20 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
>  		goto out;
>  	}
>  
> -	/* prime objects have no backing filp to GEM pread/pwrite
> -	 * pages from.
> -	 */
> -	if (!obj->base.filp) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> -
>  	trace_i915_gem_object_pread(obj, args->offset, args->size);
>  
> -	ret = i915_gem_shmem_pread(dev, obj, args, file);
> +	/* pread for non shmem backed objects */
> +	if (!obj->base.filp) {
> +		if (obj->tiling_mode == I915_TILING_NONE)

pread/pwrite is defined as a cpu linear, the restriction upon tiling is
a simplification of handling swizzling.

> +			ret = i915_gem_gtt_pread_pwrite(dev, obj, args->size,
> +							args->offset,
> +							args->data_ptr,
> +							false);
> +		else
> +			ret = -EINVAL;
> +	} else {
> +		ret = i915_gem_shmem_pread(dev, obj, args, file);
> +	}
>  
>  out:
>  	drm_gem_object_unreference(&obj->base);
> @@ -1105,17 +1204,22 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
>  		goto out;
>  	}
>  
> -	/* prime objects have no backing filp to GEM pread/pwrite
> -	 * pages from.
> -	 */
> -	if (!obj->base.filp) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> -
>  	trace_i915_gem_object_pwrite(obj, args->offset, args->size);
>  
>  	ret = -EFAULT;
> +
> +	/* pwrite for non shmem backed objects */
> +	if (!obj->base.filp) {
> +		if (obj->tiling_mode == I915_TILING_NONE)
> +			ret = i915_gem_gtt_pread_pwrite(dev, obj, args->size,
> +							args->offset,
> +							args->data_ptr,
> +							true);
> +		else
> +			ret = -EINVAL;
> +
> +		goto out;

The fast pwrite code always works for obj->base.filp == NULL. To easily
make it generic and handle the cases where we cannot fallback to shem,
undo the PIN_NONBLOCK.

Then you just want something like
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d3016f37cd4d..f2284a27dd6d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1114,8 +1114,9 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
         * perspective, requiring manual detiling by the client.
         */
        if (obj->tiling_mode == I915_TILING_NONE &&
-           obj->base.write_domain != I915_GEM_DOMAIN_CPU &&
-           cpu_write_needs_clflush(obj)) {
+           (obj->base.filp == NULL ||
+            (obj->base.write_domain != I915_GEM_DOMAIN_CPU &&
+             cpu_write_needs_clflush(obj)))) {
                ret = i915_gem_gtt_pwrite_fast(dev_priv, obj, args, file);
                /* Note that the gtt paths might fail with non-page-backed user
                 * pointers (e.g. gtt mappings when moving data between
@@ -1125,7 +1126,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
        if (ret == -EFAULT || ret == -ENOSPC) {
                if (obj->phys_handle)
                        ret = i915_gem_phys_pwrite(obj, args, file);
-               else
+               else if (obj->filp)
                        ret = i915_gem_shmem_pwrite(dev, obj, args, file);
        }
 

to enable pwrite access to stolen.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre