Re: [Intel-gfx] [PATCH v1 3/4] drm/i915: Split i915_gem_init_stolen()

[Lucas De Marchi <lucas.demarchi@intel.com>]

On Fri, Sep 16, 2022 at 05:50:33PM +0530, Iddamsetty, Aravind wrote:
>
>
>On 16-09-2022 02:09, Lucas De Marchi wrote:
>> Add some helpers: adjust_stolen(), request_smem_stolen_() and
>> init_reserved_stolen() that are now called by i915_gem_init_stolen() to
>> initialize each part of the Data Stolen Memory region. Main goal is to
>> split the reserved part, also known as WOPCM, as its calculation changes
>> often per platform.
>>
>> This also fixes a bug in graphics version < 5 (in theory, not tested,
>> due to no machine available): it would bail out on stolen creation due
>> to "Stolen reserved area outside stolen memory". Other than that, no
>> change in behavior.
>>
>> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> index c34065fe2ecc..0e57a6d81534 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> @@ -77,22 +77,26 @@ void i915_gem_stolen_remove_node(struct drm_i915_private *i915,
>>  	mutex_unlock(&i915->mm.stolen_lock);
>>  }
>>
>> -static int i915_adjust_stolen(struct drm_i915_private *i915,
>> -			      struct resource *dsm)
>> +static bool valid_stolen_size(struct resource *dsm)
>> +{
>> +	return dsm->start != 0 && dsm->end > dsm->start;
>> +}
>> +
>> +static int adjust_stolen(struct drm_i915_private *i915,
>> +			 struct resource *dsm)
>>  {
>>  	struct i915_ggtt *ggtt = to_gt(i915)->ggtt;
>>  	struct intel_uncore *uncore = ggtt->vm.gt->uncore;
>> -	struct resource *r;
>>
>> -	if (dsm->start == 0 || dsm->end <= dsm->start)
>> +	if (!valid_stolen_size(dsm))
>>  		return -EINVAL;
>>
>>  	/*
>> +	 * Make sure we don't clobber the GTT if it's within stolen memory
>> +	 *
>>  	 * TODO: We have yet too encounter the case where the GTT wasn't at the
>>  	 * end of stolen. With that assumption we could simplify this.
>>  	 */
>> -
>> -	/* Make sure we don't clobber the GTT if it's within stolen memory */
>>  	if (GRAPHICS_VER(i915) <= 4 &&
>>  	    !IS_G33(i915) && !IS_PINEVIEW(i915) && !IS_G4X(i915)) {
>>  		struct resource stolen[2] = {*dsm, *dsm};
>> @@ -131,10 +135,20 @@ static int i915_adjust_stolen(struct drm_i915_private *i915,
>>  		}
>>  	}
>>
>> +	if (!valid_stolen_size(dsm))
>> +		return -EINVAL;
>> +
>> +	return 0;
>> +}
>> +
>> +static int request_smem_stolen(struct drm_i915_private *i915,
>> +			       struct resource *dsm)
>> +{
>> +	struct resource *r;
>> +
>>  	/*
>> -	 * With stolen lmem, we don't need to check if the address range
>> -	 * overlaps with the non-stolen system memory range, since lmem is local
>> -	 * to the gpu.
>> +	 * With stolen lmem, we don't need to request if the address range
>replace /if/for
>> +	 * since lmem is local to the gpu.

humn.. it seems I skip some words here.

With stolen lmem, we don't need to request system memory since the
stolen region is local to the gpu.


>>  	 */
>>  	if (HAS_LMEM(i915))
>>  		return 0;
>> @@ -392,39 +406,22 @@ static void icl_get_stolen_reserved(struct drm_i915_private *i915,
>>  	}
>>  }
>>
>> -static int i915_gem_init_stolen(struct intel_memory_region *mem)
>> +/*
>> + * Initialize i915->dsm_reserved to contain the reserved space within the Data
>> + * Stolen Memory. This is a range on the top of DSM that is reserved, not to
>> + * be used by driver, so must be excluded from the region passed to the
>> + * allocator later. In the spec this is also called as WOPCM.
>> + *
>> + * Our expectation is that the reserved space is at the top of the stolen
>> + * region, as it has been the case for every platform, and *never* at the
>> + * bottom, so the calculation here can be simplified.
>> + */
>> +static int init_reserved_stolen(struct drm_i915_private *i915)
>>  {
>> -	struct drm_i915_private *i915 = mem->i915;
>>  	struct intel_uncore *uncore = &i915->uncore;
>>  	resource_size_t reserved_base, stolen_top;
>> -	resource_size_t reserved_total, reserved_size;
>> -
>> -	mutex_init(&i915->mm.stolen_lock);
>> -
>> -	if (intel_vgpu_active(i915)) {
>> -		drm_notice(&i915->drm,
>> -			   "%s, disabling use of stolen memory\n",
>> -			   "iGVT-g active");
>> -		return 0;
>> -	}
>> -
>> -	if (i915_vtd_active(i915) && GRAPHICS_VER(i915) < 8) {
>> -		drm_notice(&i915->drm,
>> -			   "%s, disabling use of stolen memory\n",
>> -			   "DMAR active");
>> -		return 0;
>> -	}
>> -
>> -	if (resource_size(&mem->region) == 0)
>> -		return 0;
>> -
>> -	if (i915_adjust_stolen(i915, &mem->region))
>> -		return 0;
>> -
>> -	GEM_BUG_ON(i915->dsm.start == 0);
>> -	GEM_BUG_ON(i915->dsm.end <= i915->dsm.start);
>> -
>> -	i915->dsm = mem->region;
>> +	resource_size_t reserved_size;
>> +	int ret = 0;
>>
>>  	stolen_top = i915->dsm.end + 1;
>>  	reserved_base = stolen_top;
>> @@ -453,19 +450,17 @@ static int i915_gem_init_stolen(struct intel_memory_region *mem)
>>  	} else if (GRAPHICS_VER(i915) >= 5 || IS_G4X(i915)) {
>>  		g4x_get_stolen_reserved(i915, uncore,
>>  					&reserved_base, &reserved_size);
>> +	} else {
>> +		/* No reserved region */
>> +		goto bail_out;
>
>better to have a WARN_ON here about STOLEN region wrongly passed on the
>region list.

see the follow up I sent on this patch. The bail out here should be outside
this else and is a normal condition. This is about the reserved space
within stolen (aka wopcm), and having it 0 is normal even for the
platforms above that have a function to read the stolen reserved region.

a WARN_ON based on the regions in device_info would be wrong as having
stolen doesn't mean there is a wopcm. Btw I think a great source of
confusion is using "reserved stolen" for this part because we then think
it's about reserving the stolen memory when in fact this is about a
region inside the stolen.

>
>>  	}
>>
>> -	/*
>> -	 * Our expectation is that the reserved space is at the top of the
>> -	 * stolen region and *never* at the bottom. If we see !reserved_base,
>> -	 * it likely means we failed to read the registers correctly.
>> -	 */
>> -	if (!reserved_base) {
>> +	if (!reserved_base || reserved_base == stolen_top) {
>>  		drm_err(&i915->drm,
>>  			"inconsistent reservation %pa + %pa; ignoring\n",
>>  			&reserved_base, &reserved_size);
>> -		reserved_base = stolen_top;
>> -		reserved_size = 0;
>> +		ret = -EINVAL;
>> +		goto bail_out;
>>  	}
>>
>>  	i915->dsm_reserved =
>> @@ -475,19 +470,55 @@ static int i915_gem_init_stolen(struct intel_memory_region *mem)
>>  		drm_err(&i915->drm,
>>  			"Stolen reserved area %pR outside stolen memory %pR\n",
>>  			&i915->dsm_reserved, &i915->dsm);
>> +		ret = -EINVAL;
>> +		goto bail_out;
>> +	}
>> +
>> +	return 0;
>> +
>> +bail_out:
>> +	i915->dsm_reserved =
>> +		(struct resource)DEFINE_RES_MEM(reserved_base, 0);
>> +
>> +	return ret;
>> +}
>> +
>> +static int i915_gem_init_stolen(struct intel_memory_region *mem)
>> +{
>> +	struct drm_i915_private *i915 = mem->i915;
>> +
>> +	mutex_init(&i915->mm.stolen_lock);
>> +
>> +	if (intel_vgpu_active(i915)) {
>> +		drm_notice(&i915->drm,
>> +			   "%s, disabling use of stolen memory\n",
>> +			   "iGVT-g active");
>> +		return 0;
>> +	}
>> +
>> +	if (i915_vtd_active(i915) && GRAPHICS_VER(i915) < 8) {
>> +		drm_notice(&i915->drm,
>> +			   "%s, disabling use of stolen memory\n",
>> +			   "DMAR active");
>>  		return 0;
>>  	}
>>
>> +	if (adjust_stolen(i915, &mem->region))
>> +		return 0;
>> +
>> +	if (request_smem_stolen(i915, &mem->region))
>> +		return 0;
>
>why do we want to subside the errors returned in adjust_stolen and
>request_smem_stolen?

This was already there: i915_gem_init_stolen() was only returning 0.
This patch only makes it clearer since it's now a smaller function.

Basically this was the function doing the "log when
appropriate, but consider it non-fatal". On the next patch I move this
decision to the caller.


Lucas De Marchi

>
>> +
>> +	i915->dsm = mem->region;
>> +
>> +	if (init_reserved_stolen(i915))
>similarly here.
>
>Thanks,
>Aravind.
>> +		return 0;
>> +
>>  	/* Exclude the reserved region from driver use */
>> -	mem->region.end = reserved_base - 1;
>> +	mem->region.end = i915->dsm_reserved.start - 1;
>>  	mem->io_size = min(mem->io_size, resource_size(&mem->region));
>>
>> -	/* It is possible for the reserved area to end before the end of stolen
>> -	 * memory, so just consider the start. */
>> -	reserved_total = stolen_top - reserved_base;
>> -
>> -	i915->stolen_usable_size =
>> -		resource_size(&i915->dsm) - reserved_total;
>> +	i915->stolen_usable_size = resource_size(&mem->region);
>>
>>  	drm_dbg(&i915->drm,
>>  		"Memory reserved for graphics device: %lluK, usable: %lluK\n",
>> @@ -759,11 +790,6 @@ static int init_stolen_lmem(struct intel_memory_region *mem)
>>  	if (GEM_WARN_ON(resource_size(&mem->region) == 0))
>>  		return -ENODEV;
>>
>> -	/*
>> -	 * TODO: For stolen lmem we mostly just care about populating the dsm
>> -	 * related bits and setting up the drm_mm allocator for the range.
>> -	 * Perhaps split up i915_gem_init_stolen() for this.
>> -	 */
>>  	err = i915_gem_init_stolen(mem);
>>  	if (err)
>>  		return err;
>>