Re: [Intel-gfx] [PATCH 1/3] drm/i915: Set I915_BO_ALLOC_USER for framebuffer

[Matthew Auld <matthew.auld@intel.com>]

On 06/03/2023 12:07, Nirmoy Das wrote:
> Framebuffer is exposed to userspace so set I915_BO_ALLOC_USER
> flag for it. This also make sure that ttm allocates offset
> for lmem objects.
> 
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_dpt.c           | 4 +++-
>   drivers/gpu/drm/i915/display/intel_fbdev.c         | 3 ++-
>   drivers/gpu/drm/i915/display/intel_plane_initial.c | 3 ++-
>   3 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dpt.c b/drivers/gpu/drm/i915/display/intel_dpt.c
> index ad1a37b515fb..2e6238881860 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpt.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpt.c
> @@ -254,7 +254,9 @@ intel_dpt_create(struct intel_framebuffer *fb)
>   
>   	size = round_up(size * sizeof(gen8_pte_t), I915_GTT_PAGE_SIZE);
>   
> -	dpt_obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_CONTIGUOUS);
> +	dpt_obj = i915_gem_object_create_lmem(i915, size,
> +					      I915_BO_ALLOC_CONTIGUOUS |
> +					      I915_BO_ALLOC_USER);

AFAICT this is just some driver internal stuff for display page-table, 
which gets mapped through GGTT or something, and is not the actual fb. 
Is it really exposed to the user?

>   	if (IS_ERR(dpt_obj) && i915_ggtt_has_aperture(to_gt(i915)->ggtt))
>   		dpt_obj = i915_gem_object_create_stolen(i915, size);
>   	if (IS_ERR(dpt_obj) && !HAS_LMEM(i915)) {
> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> index 3659350061a7..98ae3a3a986a 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -163,7 +163,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>   	obj = ERR_PTR(-ENODEV);
>   	if (HAS_LMEM(dev_priv)) {
>   		obj = i915_gem_object_create_lmem(dev_priv, size,
> -						  I915_BO_ALLOC_CONTIGUOUS);
> +						  I915_BO_ALLOC_CONTIGUOUS |
> +						  I915_BO_ALLOC_USER);
>   	} else {
>   		/*
>   		 * If the FB is too big, just don't use it since fbdev is not very
> diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> index bb6ea7de5c61..4a3680f6a3f5 100644
> --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
> +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> @@ -110,7 +110,8 @@ initial_plane_vma(struct drm_i915_private *i915,
>   	    size * 2 > i915->dsm.usable_size)
>   		return NULL;
>   
> -	obj = i915_gem_object_create_region_at(mem, phys_base, size, 0);
> +	obj = i915_gem_object_create_region_at(mem, phys_base, size,
> +					       I915_BO_ALLOC_USER);

ALLOC_USER has the side effect of also zeroing the memory underneath, 
IIRC. However this here is the pre-allocated fb (will have some boot 
logo stuff), so we shouldn't ever clear it.

>   	if (IS_ERR(obj))
>   		return NULL;
>