Re: [Intel-gfx] [PATCH v2 2/2] drm/i915/display: Do not use stolen on MTL

[Nirmoy Das <nirmoy.das@linux.intel.com>]

On 7/12/2023 12:06 AM, Nirmoy Das wrote:
> Use smem on MTL due to a HW bug in MTL that prevents
> reading from stolen memory using LMEM BAR.
>
> v2: improve stolen skip detection(Andrzej)
>
> Cc: Oak Zeng <oak.zeng@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Andi Shyti <andi.shyti@linux.intel.com>
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> Reviewed-by: Oak Zeng <oak.zeng@intel.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_fbdev.c   | 5 ++++-
>   drivers/gpu/drm/i915/display/intel_overlay.c | 5 +++--
>   2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> index 1cc0ddc6a310..e019bbcd474e 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -187,8 +187,11 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>   		 * If the FB is too big, just don't use it since fbdev is not very
>   		 * important and we should probably use that space with FBC or other
>   		 * features.
> +		 *
> +		 * Also skip stolen on MTL as Wa_22018444074 mitigation.
>   		 */
> -		if (size * 2 < dev_priv->dsm.usable_size)
> +		if (size * 2 < dev_priv->dsm.usable_size ||
> +		    !(IS_METEORLAKE(dev_priv)))

Just realized  this is wrong, stolen will be picked on non-mtl even if 
the stolen usable size is < 2*size which is not expected.

I will keep this as v1


Regards,

Nirmoy

>   			obj = i915_gem_object_create_stolen(dev_priv, size);
>   		if (IS_ERR(obj))
>   			obj = i915_gem_object_create_shmem(dev_priv, size);
> diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c b/drivers/gpu/drm/i915/display/intel_overlay.c
> index d6fe2bbabe55..09c1aa1427ad 100644
> --- a/drivers/gpu/drm/i915/display/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
> @@ -1348,11 +1348,12 @@ int intel_overlay_attrs_ioctl(struct drm_device *dev, void *data,
>   static int get_registers(struct intel_overlay *overlay, bool use_phys)
>   {
>   	struct drm_i915_private *i915 = overlay->i915;
> -	struct drm_i915_gem_object *obj;
> +	struct drm_i915_gem_object *obj = ERR_PTR(-ENODEV);
>   	struct i915_vma *vma;
>   	int err;
>   
> -	obj = i915_gem_object_create_stolen(i915, PAGE_SIZE);
> +	if (!IS_METEORLAKE(i915)) /* Wa_22018444074 */
> +		obj = i915_gem_object_create_stolen(i915, PAGE_SIZE);
>   	if (IS_ERR(obj))
>   		obj = i915_gem_object_create_internal(i915, PAGE_SIZE);
>   	if (IS_ERR(obj))