drm/i915: add support for specifying DMC firmware override by module param

Use i915.dmc_firmware_path to override default firmware for the platform
and bypassing version checks.

v2: add missing param struct member declaration (David)
Tested-by: David Weinehall <david.weinehall@linux.intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: David Weinehall <david.weinehall@linux.intel.com>
Acked-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180424122016.2416-1-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_params.c

@@ -164,6 +164,9 @@ i915_param_named_unsafe(guc_firmware_path, charp, 0400,
 i915_param_named_unsafe(huc_firmware_path, charp, 0400,
 	"HuC firmware path to use instead of the default one");
 
+i915_param_named_unsafe(dmc_firmware_path, charp, 0400,
+	"DMC firmware path to use instead of the default one");
+
 i915_param_named_unsafe(enable_dp_mst, bool, 0600,
 	"Enable multi-stream transport (MST) for new DisplayPort sinks. (default: true)");
 

drivers/gpu/drm/i915/i915_params.h

@@ -51,6 +51,7 @@ struct drm_printer;
 	param(int, guc_log_level, -1) \
 	param(char *, guc_firmware_path, NULL) \
 	param(char *, huc_firmware_path, NULL) \
+	param(char *, dmc_firmware_path, NULL) \
 	param(int, mmio_debug, 0) \
 	param(int, edp_vswing, 0) \
 	param(int, reset, 2) \

drivers/gpu/drm/i915/intel_csr.c

@@ -298,7 +298,10 @@ static uint32_t *parse_csr_fw(struct drm_i915_private *dev_priv,
 
 	csr->version = css_header->version;
 
-	if (IS_CANNONLAKE(dev_priv)) {
+	if (csr->fw_path == i915_modparams.dmc_firmware_path) {
+		/* Bypass version check for firmware override. */
+		required_version = csr->version;
+	} else if (IS_CANNONLAKE(dev_priv)) {
 		required_version = CNL_CSR_VERSION_REQUIRED;
 	} else if (IS_GEMINILAKE(dev_priv)) {
 		required_version = GLK_CSR_VERSION_REQUIRED;
@@ -453,7 +456,9 @@ void intel_csr_ucode_init(struct drm_i915_private *dev_priv)
 	if (!HAS_CSR(dev_priv))
 		return;
 
-	if (IS_CANNONLAKE(dev_priv))
+	if (i915_modparams.dmc_firmware_path)
+		csr->fw_path = i915_modparams.dmc_firmware_path;
+	else if (IS_CANNONLAKE(dev_priv))
 		csr->fw_path = I915_CSR_CNL;
 	else if (IS_GEMINILAKE(dev_priv))
 		csr->fw_path = I915_CSR_GLK;