drm/i915/guc: Add documentation for MMIO based communication

As we are going to extend our use of MMIO based communication,
try to explain its mechanics and update corresponding definitions.

v2: fix checkpatch MACRO_ARG_REUSE
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Kelvin Gardiner <kelvin.gardiner@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com> #1
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326194829.58836-2-michal.wajdeczko@intel.com

drivers/gpu/drm/i915/intel_guc.c

@@ -329,6 +329,9 @@ int intel_guc_send_mmio(struct intel_guc *guc, const u32 *action, u32 len)
 	GEM_BUG_ON(!len);
 	GEM_BUG_ON(len > guc->send_regs.count);
 
+	/* We expect only action code */
+	GEM_BUG_ON(*action & ~INTEL_GUC_MSG_CODE_MASK);
+
 	/* If CT is available, we expect to use MMIO only during init/fini */
 	GEM_BUG_ON(HAS_GUC_CT(dev_priv) &&
 		*action != INTEL_GUC_ACTION_REGISTER_COMMAND_TRANSPORT_BUFFER &&
@@ -350,18 +353,15 @@ int intel_guc_send_mmio(struct intel_guc *guc, const u32 *action, u32 len)
 	 */
 	ret = __intel_wait_for_register_fw(dev_priv,
 					   guc_send_reg(guc, 0),
-					   INTEL_GUC_RECV_MASK,
-					   INTEL_GUC_RECV_MASK,
+					   INTEL_GUC_MSG_TYPE_MASK,
+					   INTEL_GUC_MSG_TYPE_RESPONSE <<
+					   INTEL_GUC_MSG_TYPE_SHIFT,
 					   10, 10, &status);
-	if (status != INTEL_GUC_STATUS_SUCCESS) {
-		/*
-		 * Either the GuC explicitly returned an error (which
-		 * we convert to -EIO here) or no response at all was
-		 * received within the timeout limit (-ETIMEDOUT)
-		 */
-		if (ret != -ETIMEDOUT)
-			ret = -EIO;
+	/* If GuC explicitly returned an error, convert it to -EIO */
+	if (!ret && !INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(status))
+		ret = -EIO;
 
+	if (ret) {
 		DRM_DEBUG_DRIVER("INTEL_GUC_SEND: Action 0x%X failed;"
 				 " ret=%d status=0x%08X response=0x%08X\n",
 				 action[0], ret, status,

drivers/gpu/drm/i915/intel_guc_ct.c

@@ -398,7 +398,7 @@ static int ctch_send(struct intel_guc *guc,
 	err = wait_for_response(desc, fence, status);
 	if (unlikely(err))
 		return err;
-	if (*status != INTEL_GUC_STATUS_SUCCESS)
+	if (!INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(*status))
 		return -EIO;
 	return 0;
 }

drivers/gpu/drm/i915/intel_guc_fwif.h

@@ -560,7 +560,68 @@ struct guc_shared_ctx_data {
 	struct guc_ctx_report preempt_ctx_report[GUC_MAX_ENGINES_NUM];
 } __packed;
 
-/* This Action will be programmed in C180 - SOFT_SCRATCH_O_REG */
+/**
+ * DOC: MMIO based communication
+ *
+ * The MMIO based communication between Host and GuC uses software scratch
+ * registers, where first register holds data treated as message header,
+ * and other registers are used to hold message payload.
+ *
+ * For Gen9+, GuC uses software scratch registers 0xC180-0xC1B8
+ *
+ *      +-----------+---------+---------+---------+
+ *      |  MMIO[0]  | MMIO[1] |   ...   | MMIO[n] |
+ *      +-----------+---------+---------+---------+
+ *      | header    |      optional payload       |
+ *      +======+====+=========+=========+=========+
+ *      | 31:28|type|         |         |         |
+ *      +------+----+         |         |         |
+ *      | 27:16|data|         |         |         |
+ *      +------+----+         |         |         |
+ *      |  15:0|code|         |         |         |
+ *      +------+----+---------+---------+---------+
+ *
+ * The message header consists of:
+ *
+ * - **type**, indicates message type
+ * - **code**, indicates message code, is specific for **type**
+ * - **data**, indicates message data, optional, depends on **code**
+ *
+ * The following message **types** are supported:
+ *
+ * - **REQUEST**, indicates Host-to-GuC request, requested GuC action code
+ *   must be priovided in **code** field. Optional action specific parameters
+ *   can be provided in remaining payload registers or **data** field.
+ *
+ * - **RESPONSE**, indicates GuC-to-Host response from earlier GuC request,
+ *   action response status will be provided in **code** field. Optional
+ *   response data can be returned in remaining payload registers or **data**
+ *   field.
+ */
+
+#define INTEL_GUC_MSG_TYPE_SHIFT	28
+#define INTEL_GUC_MSG_TYPE_MASK		(0xF << INTEL_GUC_MSG_TYPE_SHIFT)
+#define INTEL_GUC_MSG_DATA_SHIFT	16
+#define INTEL_GUC_MSG_DATA_MASK		(0xFFF << INTEL_GUC_MSG_DATA_SHIFT)
+#define INTEL_GUC_MSG_CODE_SHIFT	0
+#define INTEL_GUC_MSG_CODE_MASK		(0xFFFF << INTEL_GUC_MSG_CODE_SHIFT)
+
+#define __INTEL_GUC_MSG_GET(T, m) \
+	(((m) & INTEL_GUC_MSG_ ## T ## _MASK) >> INTEL_GUC_MSG_ ## T ## _SHIFT)
+#define INTEL_GUC_MSG_TO_TYPE(m)	__INTEL_GUC_MSG_GET(TYPE, m)
+#define INTEL_GUC_MSG_TO_DATA(m)	__INTEL_GUC_MSG_GET(DATA, m)
+#define INTEL_GUC_MSG_TO_CODE(m)	__INTEL_GUC_MSG_GET(CODE, m)
+
+enum intel_guc_msg_type {
+	INTEL_GUC_MSG_TYPE_REQUEST = 0x0,
+	INTEL_GUC_MSG_TYPE_RESPONSE = 0xF,
+};
+
+#define __INTEL_GUC_MSG_TYPE_IS(T, m) \
+	(INTEL_GUC_MSG_TO_TYPE(m) == INTEL_GUC_MSG_TYPE_ ## T)
+#define INTEL_GUC_MSG_IS_REQUEST(m)	__INTEL_GUC_MSG_TYPE_IS(REQUEST, m)
+#define INTEL_GUC_MSG_IS_RESPONSE(m)	__INTEL_GUC_MSG_TYPE_IS(RESPONSE, m)
+
 enum intel_guc_action {
 	INTEL_GUC_ACTION_DEFAULT = 0x0,
 	INTEL_GUC_ACTION_REQUEST_PREEMPTION = 0x2,
@@ -597,24 +658,17 @@ enum intel_guc_report_status {
 #define GUC_LOG_CONTROL_VERBOSITY_MASK	(0xF << GUC_LOG_CONTROL_VERBOSITY_SHIFT)
 #define GUC_LOG_CONTROL_DEFAULT_LOGGING	(1 << 8)
 
-/*
- * The GuC sends its response to a command by overwriting the
- * command in SS0. The response is distinguishable from a command
- * by the fact that all the MASK bits are set. The remaining bits
- * give more detail.
- */
-#define	INTEL_GUC_RECV_MASK	((u32)0xF0000000)
-#define	INTEL_GUC_RECV_IS_RESPONSE(x)	((u32)(x) >= INTEL_GUC_RECV_MASK)
-#define	INTEL_GUC_RECV_STATUS(x)	(INTEL_GUC_RECV_MASK | (x))
-
-/* GUC will return status back to SOFT_SCRATCH_O_REG */
-enum intel_guc_status {
-	INTEL_GUC_STATUS_SUCCESS = INTEL_GUC_RECV_STATUS(0x0),
-	INTEL_GUC_STATUS_ALLOCATE_DOORBELL_FAIL = INTEL_GUC_RECV_STATUS(0x10),
-	INTEL_GUC_STATUS_DEALLOCATE_DOORBELL_FAIL = INTEL_GUC_RECV_STATUS(0x20),
-	INTEL_GUC_STATUS_GENERIC_FAIL = INTEL_GUC_RECV_STATUS(0x0000F000)
+enum intel_guc_response_status {
+	INTEL_GUC_RESPONSE_STATUS_SUCCESS = 0x0,
+	INTEL_GUC_RESPONSE_STATUS_GENERIC_FAIL = 0xF000,
 };
 
+#define INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(m) \
+	 (typecheck(u32, (m)) && \
+	  ((m) & (INTEL_GUC_MSG_TYPE_MASK | INTEL_GUC_MSG_CODE_MASK)) == \
+	  ((INTEL_GUC_MSG_TYPE_RESPONSE << INTEL_GUC_MSG_TYPE_SHIFT) | \
+	   (INTEL_GUC_RESPONSE_STATUS_SUCCESS << INTEL_GUC_MSG_CODE_SHIFT)))
+
 /* This action will be programmed in C1BC - SOFT_SCRATCH_15_REG */
 enum intel_guc_recv_message {
 	INTEL_GUC_RECV_MSG_CRASH_DUMP_POSTED = BIT(1),