drm/i915: Add lmem_bar_size modparam

For testing purposes, support forcing the lmem_bar_size through a new
modparam. In CI we only have a limited number of configurations for DG2,
but we still need to be reasonably sure we get a usable device (also
verifying we report the correct values for things like
probed_cpu_visible_size etc) with all the potential lmem_bar sizes that
we might expect see in the wild.

v2: Update commit message and a minor modification.(Matt)

v3: Optimised lmem bar size code and modified code to resize
bar maximum upto lmem_size instead of maximum supported size.(Nirmoy)

v4: Optimised lmem bar size code.(Nirmoy)
Signed-off-by: Priyanka Dandamudi <priyanka.dandamudi@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220713130209.2573233-3-priyanka.dandamudi@intel.com

drivers/gpu/drm/i915/gt/intel_region_lmem.c

@@ -51,15 +51,39 @@ static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t
 	struct pci_bus *root = pdev->bus;
 	struct resource *root_res;
 	resource_size_t rebar_size;
+	resource_size_t current_size;
 	u32 pci_cmd;
 	int i;
 
-	rebar_size = roundup_pow_of_two(pci_resource_len(pdev, LMEM_BAR_NUM));
+	current_size = roundup_pow_of_two(pci_resource_len(pdev, LMEM_BAR_NUM));
+
+	if (i915->params.lmem_bar_size) {
+		u32 bar_sizes;
+
+		rebar_size = i915->params.lmem_bar_size *
+			(resource_size_t)SZ_1M;
+		bar_sizes = pci_rebar_get_possible_sizes(pdev,
+							 LMEM_BAR_NUM);
+
+		if (rebar_size == current_size)
+			return;
+
+		if (!(bar_sizes & BIT(pci_rebar_bytes_to_size(rebar_size))) ||
+		    rebar_size >= roundup_pow_of_two(lmem_size)) {
+			rebar_size = lmem_size;
+
+			drm_info(&i915->drm,
+				 "Given bar size is not within supported size, setting it to default: %llu\n",
+				 (u64)lmem_size >> 20);
+		}
+	} else {
+		rebar_size = current_size;
 
 		if (rebar_size != roundup_pow_of_two(lmem_size))
 			rebar_size = lmem_size;
 		else
 			return;
+	}
 
 	/* Find out if root bus contains 64bit memory addressing */
 	while (root->parent)

drivers/gpu/drm/i915/i915_params.c

@@ -204,6 +204,8 @@ i915_param_named_unsafe(request_timeout_ms, uint, 0600,
 
 i915_param_named_unsafe(lmem_size, uint, 0400,
 			"Set the lmem size(in MiB) for each region. (default: 0, all memory)");
+i915_param_named_unsafe(lmem_bar_size, uint, 0400,
+			"Set the lmem bar size(in MiB).");
 
 static __always_inline void _print_param(struct drm_printer *p,
 					 const char *name,

drivers/gpu/drm/i915/i915_params.h

@@ -74,6 +74,7 @@ struct drm_printer;
 	param(char *, force_probe, CONFIG_DRM_I915_FORCE_PROBE, 0400) \
 	param(unsigned int, request_timeout_ms, CONFIG_DRM_I915_REQUEST_TIMEOUT, CONFIG_DRM_I915_REQUEST_TIMEOUT ? 0600 : 0) \
 	param(unsigned int, lmem_size, 0, 0400) \
+	param(unsigned int, lmem_bar_size, 0, 0400) \
 	/* leave bools at the end to not create holes */ \
 	param(bool, enable_hangcheck, true, 0600) \
 	param(bool, load_detect_test, false, 0600) \