linux-kernel - Re: [PATCH v8 01/10] drm/i915/ttm: dont trample cache

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Date:   Wed, 22 Jun 2022 12:44:59 +0200
From:   Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
To:     Robert Beckett <bob.beckett@...labora.com>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     kernel@...labora.com, Matthew Auld <matthew.auld@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 01/10] drm/i915/ttm: dont trample cache_level overrides
 during ttm move


On 6/21/22 22:00, Robert Beckett wrote:
> Various places within the driver override the default chosen cache_level.
> Before ttm, these overrides were permanent until explicitly changed again
> or for the lifetime of the buffer.
>
> TTM movement code came along and decided that it could make that
> decision at that time, which is usually well after object creation, so
> overrode the cache_level decision and reverted it back to its default
> decision.
>
> Add logic to indicate whether the caching mode has been set by anything
> other than the move logic. If so, assume that the code that overrode the
> defaults knows best and keep it.
>
> Signed-off-by: Robert Beckett <bob.beckett@...labora.com>

LGTM.

Reviewed-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>


> ---
>   drivers/gpu/drm/i915/gem/i915_gem_object.c       | 1 +
>   drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 1 +
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c          | 1 +
>   drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c     | 9 ++++++---
>   4 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> index 06b1b188ce5a..519887769c08 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> @@ -125,6 +125,7 @@ void i915_gem_object_set_cache_coherency(struct drm_i915_gem_object *obj,
>   	struct drm_i915_private *i915 = to_i915(obj->base.dev);
>   
>   	obj->cache_level = cache_level;
> +	obj->ttm.cache_level_override = true;
>   
>   	if (cache_level != I915_CACHE_NONE)
>   		obj->cache_coherent = (I915_BO_CACHE_COHERENT_FOR_READ |
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> index 2c88bdb8ff7c..6632ed52e919 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> @@ -605,6 +605,7 @@ struct drm_i915_gem_object {
>   		struct i915_gem_object_page_iter get_io_page;
>   		struct drm_i915_gem_object *backup;
>   		bool created:1;
> +		bool cache_level_override:1;
>   	} ttm;
>   
>   	/*
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 4c25d9b2f138..27d59639177f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -1241,6 +1241,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
>   	i915_gem_object_init_memory_region(obj, mem);
>   	i915_ttm_adjust_domains_after_move(obj);
>   	i915_ttm_adjust_gem_after_move(obj);
> +	obj->ttm.cache_level_override = false;
>   	i915_gem_object_unlock(obj);
>   
>   	return 0;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> index a10716f4e717..4c1de0b4a10f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> @@ -123,9 +123,12 @@ void i915_ttm_adjust_gem_after_move(struct drm_i915_gem_object *obj)
>   	obj->mem_flags |= i915_ttm_cpu_maps_iomem(bo->resource) ? I915_BO_FLAG_IOMEM :
>   		I915_BO_FLAG_STRUCT_PAGE;
>   
> -	cache_level = i915_ttm_cache_level(to_i915(bo->base.dev), bo->resource,
> -					   bo->ttm);
> -	i915_gem_object_set_cache_coherency(obj, cache_level);
> +	if (!obj->ttm.cache_level_override) {
> +		cache_level = i915_ttm_cache_level(to_i915(bo->base.dev),
> +						   bo->resource, bo->ttm);
> +		i915_gem_object_set_cache_coherency(obj, cache_level);
> +		obj->ttm.cache_level_override = false;
> +	}
>   }
>   
>   /**