drm/i915/opregion: let user specify override VBT via firmware load

Sometimes it would be most enlightening to debug systems by replacing
the VBT to be used. For example, in the referenced bug the BIOS provides
different VBT depending on the boot mode (UEFI vs. legacy). It would be
interesting to try the failing boot mode with the VBT from the working
boot, and see if that makes a difference.

Add a module parameter to load the VBT using the firmware loader, not
unlike the EDID firmware mechanism.

As a starting point for experimenting, one can pick up the BIOS provided
VBT from /sys/kernel/debug/dri/0/i915_opregion/i915_vbt.

v2: clarify firmware load return value check (Bob)

v3: kfree the loaded firmware blob

References: https://bugs.freedesktop.org/show_bug.cgi?id=97822#c83Reviewed-by: NBob Paauwe <bob.j.paauwe@intel.com>
Acked-by: NDaniel Vetter <daniel@ffwll.ch>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170817115209.25912-1-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -646,6 +646,7 @@ struct intel_opregion {
 	u32 swsci_sbcb_sub_functions;
 	struct opregion_asle *asle;
 	void *rvda;
+	void *vbt_firmware;
 	const void *vbt;
 	u32 vbt_size;
 	u32 *lid_state;

drivers/gpu/drm/i915/i915_params.c

@@ -118,6 +118,10 @@ MODULE_PARM_DESC(vbt_sdvo_panel_type,
 module_param_named_unsafe(reset, i915.reset, int, 0600);
 MODULE_PARM_DESC(reset, "Attempt GPU resets (0=disabled, 1=full gpu reset, 2=engine reset [default])");
 
+module_param_named_unsafe(vbt_firmware, i915.vbt_firmware, charp, 0400);
+MODULE_PARM_DESC(vbt_firmware,
+		 "Load VBT from specified file under /lib/firmware");
+
 #if IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR)
 module_param_named(error_capture, i915.error_capture, bool, 0600);
 MODULE_PARM_DESC(error_capture,

drivers/gpu/drm/i915/i915_params.h

@@ -28,6 +28,7 @@
 #include <linux/cache.h> /* for __read_mostly */
 
 #define I915_PARAMS_FOR_EACH(func) \
+	func(char *, vbt_firmware); \
 	func(int, modeset); \
 	func(int, panel_ignore_lid); \
 	func(int, semaphores); \

drivers/gpu/drm/i915/intel_opregion.c

@@ -27,6 +27,7 @@
 
 #include <linux/acpi.h>
 #include <linux/dmi.h>
+#include <linux/firmware.h>
 #include <acpi/video.h>
 
 #include <drm/drmP.h>
@@ -829,6 +830,10 @@ void intel_opregion_unregister(struct drm_i915_private *dev_priv)
 		memunmap(opregion->rvda);
 		opregion->rvda = NULL;
 	}
+	if (opregion->vbt_firmware) {
+		kfree(opregion->vbt_firmware);
+		opregion->vbt_firmware = NULL;
+	}
 	opregion->header = NULL;
 	opregion->acpi = NULL;
 	opregion->swsci = NULL;
@@ -912,6 +917,43 @@ static const struct dmi_system_id intel_no_opregion_vbt[] = {
 	{ }
 };
 
+static int intel_load_vbt_firmware(struct drm_i915_private *dev_priv)
+{
+	struct intel_opregion *opregion = &dev_priv->opregion;
+	const struct firmware *fw = NULL;
+	const char *name = i915.vbt_firmware;
+	int ret;
+
+	if (!name || !*name)
+		return -ENOENT;
+
+	ret = request_firmware(&fw, name, &dev_priv->drm.pdev->dev);
+	if (ret) {
+		DRM_ERROR("Requesting VBT firmware \"%s\" failed (%d)\n",
+			  name, ret);
+		return ret;
+	}
+
+	if (intel_bios_is_valid_vbt(fw->data, fw->size)) {
+		opregion->vbt_firmware = kmemdup(fw->data, fw->size, GFP_KERNEL);
+		if (opregion->vbt_firmware) {
+			DRM_DEBUG_KMS("Found valid VBT firmware \"%s\"\n", name);
+			opregion->vbt = opregion->vbt_firmware;
+			opregion->vbt_size = fw->size;
+			ret = 0;
+		} else {
+			ret = -ENOMEM;
+		}
+	} else {
+		DRM_DEBUG_KMS("Invalid VBT firmware \"%s\"\n", name);
+		ret = -EINVAL;
+	}
+
+	release_firmware(fw);
+
+	return ret;
+}
+
 int intel_opregion_setup(struct drm_i915_private *dev_priv)
 {
 	struct intel_opregion *opregion = &dev_priv->opregion;
@@ -974,6 +1016,9 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 	if (mboxes & MBOX_ASLE_EXT)
 		DRM_DEBUG_DRIVER("ASLE extension supported\n");
 
+	if (intel_load_vbt_firmware(dev_priv) == 0)
+		goto out;
+
 	if (dmi_check_system(intel_no_opregion_vbt))
 		goto out;