drm/i915: add lmem_size modparam

lmem_size is used to limit the amount of lmem for testing purposes.
Default is to use hardware available lmem size.
Signed-off-by: CQ Tang <cq.tang@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220324143123.348590-2-matthew.auld@intel.com

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

@@ -123,6 +123,10 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
 		lmem_size = intel_uncore_read64(&i915->uncore, GEN12_GSMBASE);
 	}
 
+	if (i915->params.lmem_size > 0) {
+		lmem_size = min_t(resource_size_t, lmem_size,
+				  mul_u32_u32(i915->params.lmem_size, SZ_1M));
+	}
 
 	io_start = pci_resource_start(pdev, 2);
 	io_size = min(pci_resource_len(pdev, 2), lmem_size);

drivers/gpu/drm/i915/i915_params.c

@@ -200,6 +200,9 @@ i915_param_named_unsafe(request_timeout_ms, uint, 0600,
 			"Default request/fence/batch buffer expiration timeout.");
 #endif
 
+i915_param_named_unsafe(lmem_size, uint, 0400,
+			"Set the lmem size(in MiB) for each region. (default: 0, all memory)");
+
 static __always_inline void _print_param(struct drm_printer *p,
 					 const char *name,
 					 const char *type,

drivers/gpu/drm/i915/i915_params.h

@@ -73,6 +73,7 @@ struct drm_printer;
 	param(int, enable_dpcd_backlight, -1, 0600) \
 	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) \
 	/* leave bools at the end to not create holes */ \
 	param(bool, enable_hangcheck, true, 0600) \
 	param(bool, load_detect_test, false, 0600) \