Re: [PATCH 3/9] drm/i915: avoid the last 8mb of stolen on BDW/SKL

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Sep 14, 2015 at 03:19:57PM -0300, Paulo Zanoni wrote:
> The FBC hardware for these platforms doesn't have access to the
> bios_reserved range, so it always assumes the maximum (8mb) is used.
> So avoid this range while allocating.
> 
> This solves a bunch of FIFO underruns that happen if you end up
> putting the CFB in that memory range. On my machine, with 32mb of
> stolen, I need a 2560x1440 mode for that.
> 
> Testcase: igt/kms_frontbuffer_tracking/fbc-* (given the right setup)
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Thwe only real spec quote I was able to find is in FBC_CFB_BASE:
"The buffer must not overlap the top 8 MB of stolen memory. | BDW,SKL,EXCLUDE(BXT)"

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/i915_drv.h        |  4 ++++
>  drivers/gpu/drm/i915/i915_gem_gtt.h    |  1 +
>  drivers/gpu/drm/i915/i915_gem_stolen.c | 26 +++++++++++++++++++-------
>  drivers/gpu/drm/i915/intel_fbc.c       | 16 ++++++++++++++--
>  4 files changed, 38 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 8cf2969..1f02a5a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3173,6 +3173,10 @@ static inline void i915_gem_chipset_flush(struct drm_device *dev)
>  int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
>  				struct drm_mm_node *node, u64 size,
>  				unsigned alignment);
> +int i915_gem_stolen_insert_node_in_range(struct drm_i915_private *dev_priv,
> +					 struct drm_mm_node *node, u64 size,
> +					 unsigned alignment, u64 start,
> +					 u64 end);
>  void i915_gem_stolen_remove_node(struct drm_i915_private *dev_priv,
>  				 struct drm_mm_node *node);
>  int i915_gem_init_stolen(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> index 8275007..96ebb98 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> @@ -341,6 +341,7 @@ struct i915_gtt {
>  	struct i915_address_space base;
>  
>  	size_t stolen_size;		/* Total size of stolen memory */
> +	size_t stolen_usable_size;	/* Total size minus BIOS reserved */
>  	u64 mappable_end;		/* End offset that we can CPU map */
>  	struct io_mapping *mappable;	/* Mapping to our CPU mappable region */
>  	phys_addr_t mappable_base;	/* PA of our GMADR */
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index bf26ecc..081ef6d 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -42,9 +42,9 @@
>   * for is a boon.
>   */
>  
> -int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
> -				struct drm_mm_node *node, u64 size,
> -				unsigned alignment)
> +int i915_gem_stolen_insert_node_in_range(struct drm_i915_private *dev_priv,
> +					 struct drm_mm_node *node, u64 size,
> +					 unsigned alignment, u64 start, u64 end)
>  {
>  	int ret;
>  
> @@ -52,13 +52,23 @@ int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
>  		return -ENODEV;
>  
>  	mutex_lock(&dev_priv->mm.stolen_lock);
> -	ret = drm_mm_insert_node(&dev_priv->mm.stolen, node, size, alignment,
> -				 DRM_MM_SEARCH_DEFAULT);
> +	ret = drm_mm_insert_node_in_range(&dev_priv->mm.stolen, node, size,
> +					  alignment, start, end,
> +					  DRM_MM_SEARCH_DEFAULT);
>  	mutex_unlock(&dev_priv->mm.stolen_lock);
>  
>  	return ret;
>  }
>  
> +int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
> +				struct drm_mm_node *node, u64 size,
> +				unsigned alignment)
> +{
> +	return i915_gem_stolen_insert_node_in_range(dev_priv, node, size,
> +					alignment, 0,
> +					dev_priv->gtt.stolen_usable_size);
> +}
> +
>  void i915_gem_stolen_remove_node(struct drm_i915_private *dev_priv,
>  				 struct drm_mm_node *node)
>  {
> @@ -355,9 +365,11 @@ int i915_gem_init_stolen(struct drm_device *dev)
>  		      dev_priv->gtt.stolen_size >> 10,
>  		      (dev_priv->gtt.stolen_size - reserved_total) >> 10);
>  
> +	dev_priv->gtt.stolen_usable_size = dev_priv->gtt.stolen_size -
> +					   reserved_total;
> +
>  	/* Basic memrange allocator for stolen space */
> -	drm_mm_init(&dev_priv->mm.stolen, 0, dev_priv->gtt.stolen_size -
> -		    reserved_total);
> +	drm_mm_init(&dev_priv->mm.stolen, 0, dev_priv->gtt.stolen_usable_size);
>  
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> index db38091..6f3c2ea 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -551,6 +551,16 @@ static int find_compression_threshold(struct drm_i915_private *dev_priv,
>  {
>  	int compression_threshold = 1;
>  	int ret;
> +	u64 end;
> +
> +	/* The FBC hardware for BDW/SKL doesn't have access to the stolen
> +	 * reserved range size, so it always assumes the maximum (8mb) is used.
> +	 * If we enable FBC using a CFB on that memory range we'll get FIFO
> +	 * underruns, even if that range is not reserved by the BIOS. */
> +	if (IS_BROADWELL(dev_priv) || IS_SKYLAKE(dev_priv))
> +		end = dev_priv->gtt.stolen_size - 8 * 1024 * 1024;
> +	else
> +		end = dev_priv->gtt.stolen_usable_size;
>  
>  	/* HACK: This code depends on what we will do in *_enable_fbc. If that
>  	 * code changes, this code needs to change as well.
> @@ -560,7 +570,8 @@ static int find_compression_threshold(struct drm_i915_private *dev_priv,
>  	 */
>  
>  	/* Try to over-allocate to reduce reallocations and fragmentation. */
> -	ret = i915_gem_stolen_insert_node(dev_priv, node, size <<= 1, 4096);
> +	ret = i915_gem_stolen_insert_node_in_range(dev_priv, node, size <<= 1,
> +						   4096, 0, end);
>  	if (ret == 0)
>  		return compression_threshold;
>  
> @@ -570,7 +581,8 @@ again:
>  	    (fb_cpp == 2 && compression_threshold == 2))
>  		return 0;
>  
> -	ret = i915_gem_stolen_insert_node(dev_priv, node, size >>= 1, 4096);
> +	ret = i915_gem_stolen_insert_node_in_range(dev_priv, node, size >>= 1,
> +						   4096, 0, end);
>  	if (ret && INTEL_INFO(dev_priv)->gen <= 4) {
>  		return 0;
>  	} else if (ret) {
> -- 
> 2.5.1
> 
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-- 
Ville Syrjälä
Intel OTC
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