Re: [Intel-gfx] [PATCH 12/19] drm/i915/lmem: Bypass aperture when lmem is available

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 12/04/2021 10:05, Matthew Auld wrote:
> From: Anusha Srivatsa <anusha.srivatsa@intel.com>
> 
> In the scenario where local memory is available, we have
> rely on CPU access via lmem directly instead of aperture.
> 
> v2:
> gmch is only relevant for much older hw, therefore we can drop the
> has_aperture check since it should always be present on such platforms.
> (Chris)
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Chris P Wilson <chris.p.wilson@intel.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Cc: CQ Tang <cq.tang@intel.com>
> Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_fbdev.c | 22 +++++++++++++++-------
>   drivers/gpu/drm/i915/gem/i915_gem_lmem.c   | 15 +++++++++++++++
>   drivers/gpu/drm/i915/gem/i915_gem_lmem.h   |  5 +++++
>   drivers/gpu/drm/i915/i915_vma.c            | 19 +++++++++++++------
>   4 files changed, 48 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> index 2b37959da747..4af40229f5ec 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -139,14 +139,22 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>   	size = mode_cmd.pitches[0] * mode_cmd.height;
>   	size = PAGE_ALIGN(size);
>   
> -	/* 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. */
>   	obj = ERR_PTR(-ENODEV);
> -	if (size * 2 < dev_priv->stolen_usable_size)
> -		obj = i915_gem_object_create_stolen(dev_priv, size);
> -	if (IS_ERR(obj))
> -		obj = i915_gem_object_create_shmem(dev_priv, size);
> +	if (HAS_LMEM(dev_priv)) {
> +		obj = i915_gem_object_create_lmem(dev_priv, size,
> +						  I915_BO_ALLOC_CONTIGUOUS);

Has to be contiguous? Question for display experts I guess.

[Comes back later.] Ah for iomap? Put a comment to that effect perhaps?

> +	} else {
> +		/*
> +		 * 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.
> +		 */
> +		if (size * 2 < dev_priv->stolen_usable_size)
> +			obj = i915_gem_object_create_stolen(dev_priv, size);
> +		if (IS_ERR(obj))
> +			obj = i915_gem_object_create_shmem(dev_priv, size);
> +	}

Could we keep the IS_ERR ordered allocation order to save having to 
re-indent? Bike shed so optional..

> +
>   	if (IS_ERR(obj)) {
>   		drm_err(&dev_priv->drm, "failed to allocate framebuffer\n");
>   		return PTR_ERR(obj);
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_lmem.c b/drivers/gpu/drm/i915/gem/i915_gem_lmem.c
> index 017db8f71130..f44bdd08f7cb 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_lmem.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_lmem.c
> @@ -17,6 +17,21 @@ const struct drm_i915_gem_object_ops i915_gem_lmem_obj_ops = {
>   	.release = i915_gem_object_release_memory_region,
>   };
>   
> +void __iomem *
> +i915_gem_object_lmem_io_map(struct drm_i915_gem_object *obj,
> +			    unsigned long n,
> +			    unsigned long size)
> +{
> +	resource_size_t offset;
> +
> +	GEM_BUG_ON(!i915_gem_object_is_contiguous(obj));
> +
> +	offset = i915_gem_object_get_dma_address(obj, n);
> +	offset -= obj->mm.region->region.start;
> +
> +	return io_mapping_map_wc(&obj->mm.region->iomap, offset, size);
> +}
> +
>   bool i915_gem_object_is_lmem(struct drm_i915_gem_object *obj)
>   {
>   	struct intel_memory_region *mr = obj->mm.region;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_lmem.h b/drivers/gpu/drm/i915/gem/i915_gem_lmem.h
> index 036d53c01de9..fac6bc5a5ebb 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_lmem.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_lmem.h
> @@ -14,6 +14,11 @@ struct intel_memory_region;
>   
>   extern const struct drm_i915_gem_object_ops i915_gem_lmem_obj_ops;
>   
> +void __iomem *
> +i915_gem_object_lmem_io_map(struct drm_i915_gem_object *obj,
> +			    unsigned long n,
> +			    unsigned long size);
> +
>   bool i915_gem_object_is_lmem(struct drm_i915_gem_object *obj);
>   
>   struct drm_i915_gem_object *
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 07490db51cdc..e24d33aecac4 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -27,6 +27,7 @@
>   
>   #include "display/intel_frontbuffer.h"
>   
> +#include "gem/i915_gem_lmem.h"
>   #include "gt/intel_engine.h"
>   #include "gt/intel_engine_heartbeat.h"
>   #include "gt/intel_gt.h"
> @@ -448,9 +449,11 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
>   	void __iomem *ptr;
>   	int err;
>   
> -	if (GEM_WARN_ON(!i915_vma_is_map_and_fenceable(vma))) {
> -		err = -ENODEV;
> -		goto err;
> +	if (!i915_gem_object_is_lmem(vma->obj)) {
> +		if (GEM_WARN_ON(!i915_vma_is_map_and_fenceable(vma))) {
> +			err = -ENODEV;
> +			goto err;
> +		}
>   	}
>   
>   	GEM_BUG_ON(!i915_vma_is_ggtt(vma));
> @@ -458,9 +461,13 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
>   
>   	ptr = READ_ONCE(vma->iomap);
>   	if (ptr == NULL) {
> -		ptr = io_mapping_map_wc(&i915_vm_to_ggtt(vma->vm)->iomap,
> -					vma->node.start,
> -					vma->node.size);
> +		if (i915_gem_object_is_lmem(vma->obj))
> +			ptr = i915_gem_object_lmem_io_map(vma->obj, 0,
> +							  vma->obj->base.size);

Can the vma size be bigger than the object here? Given how below works 
of vma->node.size.

> +		else
> +			ptr = io_mapping_map_wc(&i915_vm_to_ggtt(vma->vm)->iomap,
> +						vma->node.start,
> +						vma->node.size);

Looks a bit odd that this calls the same io_mapping_map_wc as 
i915_gem_object_lmem_io_map ends up doing. Perhaps that suggests there 
should be a single helper here but I am not sure what would be elegant.

Regards,

Tvrtko

>   		if (ptr == NULL) {
>   			err = -ENOMEM;
>   			goto err;
> 
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