Re: [PATCH v2 06/11] drm/i915: Move pinning of dev_priv->kernel_context into its creator

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On ma, 2016-05-23 at 12:34 +0100, Chris Wilson wrote:
> Rather than have every context ask "am I owned by the kernel? pin!",
> move that logic into the creator of the kernel context, in order to
> improve code comprehension.
> 
> v2: Throw away the user_handle on failure to allocate the ppgtt.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_context.c | 53 +++++++++++++++------------------
>  1 file changed, 24 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index a4c6377eea32..474174c20be2 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -303,9 +303,7 @@ static struct i915_gem_context *
>  i915_gem_create_context(struct drm_device *dev,
>  			struct drm_i915_file_private *file_priv)
>  {
> -	const bool is_global_default_ctx = file_priv == NULL;
>  	struct i915_gem_context *ctx;
> -	int ret = 0;
>  
>  	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
>  
> @@ -313,30 +311,15 @@ i915_gem_create_context(struct drm_device *dev,
>  	if (IS_ERR(ctx))
>  		return ctx;
>  
> -	if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state) {
> -		/* We may need to do things with the shrinker which
> -		 * require us to immediately switch back to the default
> -		 * context. This can cause a problem as pinning the
> -		 * default context also requires GTT space which may not
> -		 * be available. To avoid this we always pin the default
> -		 * context.
> -		 */
> -		ret = i915_gem_obj_ggtt_pin(ctx->legacy_hw_ctx.rcs_state,
> -					    get_context_alignment(to_i915(dev)), 0);
> -		if (ret) {
> -			DRM_DEBUG_DRIVER("Couldn't pin %d\n", ret);
> -			goto err_destroy;
> -		}
> -	}
> -
>  	if (USES_FULL_PPGTT(dev)) {
>  		struct i915_hw_ppgtt *ppgtt = i915_ppgtt_create(dev, file_priv);
>  
> -		if (IS_ERR_OR_NULL(ppgtt)) {
> +		if (IS_ERR(ppgtt)) {
>  			DRM_DEBUG_DRIVER("PPGTT setup failed (%ld)\n",
>  					 PTR_ERR(ppgtt));
> -			ret = PTR_ERR(ppgtt);
> -			goto err_unpin;
> +			idr_remove(&file_priv->context_idr, ctx->user_handle);
> +			i915_gem_context_put(ctx);
> +			return ERR_CAST(ppgtt);
>  		}
>  
>  		ctx->ppgtt = ppgtt;
> @@ -345,14 +328,6 @@ i915_gem_create_context(struct drm_device *dev,
>  	trace_i915_context_create(ctx);
>  
>  	return ctx;
> -
> -err_unpin:
> -	if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state)
> -		i915_gem_object_ggtt_unpin(ctx->legacy_hw_ctx.rcs_state);
> -err_destroy:
> -	idr_remove(&file_priv->context_idr, ctx->user_handle);
> -	i915_gem_context_put(ctx);
> -	return ERR_PTR(ret);

Don't remove a perfectly good error path.

>  }
>  
>  static void i915_gem_context_unpin(struct i915_gem_context *ctx,
> @@ -426,6 +401,26 @@ int i915_gem_context_init(struct drm_device *dev)
>  		return PTR_ERR(ctx);
>  	}
>  
> +	if (ctx->legacy_hw_ctx.rcs_state) {
> +		int ret;
> +
> +		/* We may need to do things with the shrinker which
> +		 * require us to immediately switch back to the default
> +		 * context. This can cause a problem as pinning the
> +		 * default context also requires GTT space which may not
> +		 * be available. To avoid this we always pin the default
> +		 * context.
> +		 */
> +		ret = i915_gem_obj_ggtt_pin(ctx->legacy_hw_ctx.rcs_state,
> +					    get_context_alignment(dev_priv), 0);
> +		if (ret) {
> +			DRM_ERROR("Failed to pinned default global context (error %d)\n",
> +				  ret);
> +			i915_gem_context_put(ctx);

And please make this into teardown path.

> +			return ret;
> +		}
> +	}
> +
>  	dev_priv->kernel_context = ctx;
>  
>  	DRM_DEBUG_DRIVER("%s context support initialized\n",
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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