ASoC: SOF: special-case a part of the debug memory window

The debug memory window is split in 4KiB large pages. Page zero is
used for slot descriptors, which leaves one or two more free slots
for actual useful work. One of them is usually used for mtrace
logging, which leaves no free slots on some systems and only one such
slot on others. This commit repurposes the free space in page zero
after slot descriptors to be used as slot number 16, one higher than
the currently highest possible slot number. To improve documentation
we move the tabular representation of the window layout from
ipc4-mtrace.c to header.h.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

Author: lyakh

include/sound/sof/ipc4/header.h

@@ -541,16 +541,45 @@ struct sof_ipc4_notify_resource_data {
 	uint32_t data[6];
 } __packed __aligned(4);
 
-#define SOF_IPC4_DEBUG_DESCRIPTOR_SIZE		12 /* 3 x u32 */
-
 /*
- * The debug memory window is divided into 16 slots, and the
- * first slot is used as a recorder for the other 15 slots.
+ * The debug memory window contains up to 16 4kB large pages, where pages one to
+ * fifteen are used for user slots and page zero contains slot descriptors:
+ *
+ *	------------------------
+ *	| Page0  - descriptors |
+ *	------------------------
+ *	| Page1  - slot0       |
+ *	------------------------
+ *	| Page2  - slot1       |
+ *	------------------------
+ *	|         ...          |
+ *	------------------------
+ *	| Page14  - slot13     |
+ *	------------------------
+ *	| Page15  - slot14     |
+ *	------------------------
+ *
+ * The slot descriptor is:
+ * u32 res_id;
+ * u32 type;
+ * u32 vma;
  */
+
+#define SOF_IPC4_DEBUG_PAGE_SIZE		0x1000
+#define SOF_IPC4_DEBUG_SLOT_SIZE		SOF_IPC4_DEBUG_PAGE_SIZE
+#define SOF_IPC4_DEBUG_PAGE0_SLOT_OFFSET	1024
+
+/* Usable slots 0..14 (page 1..15) */
 #define SOF_IPC4_MAX_DEBUG_SLOTS		15
-#define SOF_IPC4_DEBUG_SLOT_SIZE		0x1000
 
-/* debug log slot types */
+/*
+ * Descriptor 0-14: slot 0-14 (page 1-15)
+ * Descriptor 15: partial slot at page 0 + 1024
+ */
+#define SOF_IPC4_MAX_DEBUG_DESCS		(SOF_IPC4_MAX_DEBUG_SLOTS + 1)
+#define SOF_IPC4_DEBUG_DESCRIPTOR_SIZE		12 /* 3 x u32 */
+
+/* Debug log slot types */
 #define SOF_IPC4_DEBUG_SLOT_UNUSED		0x00000000
 #define SOF_IPC4_DEBUG_SLOT_CRITICAL_LOG	0x54524300 /* byte 0: core ID */
 #define SOF_IPC4_DEBUG_SLOT_DEBUG_LOG		0x474f4c00 /* byte 0: core ID */

sound/soc/sof/ipc4-mtrace.c

@@ -10,31 +10,7 @@
 #include "ipc4-priv.h"
 
 /*
- * debug info window is organized in 16 (equal sized) pages:
- *
- *	------------------------
- *	| Page0  - descriptors |
- *	------------------------
- *	| Page1  - slot0       |
- *	------------------------
- *	| Page2  - slot1       |
- *	------------------------
- *	|         ...          |
- *	------------------------
- *	| Page14  - slot13     |
- *	------------------------
- *	| Page15  - slot14     |
- *	------------------------
- *
- * The slot size == page size
- *
- * The first page contains descriptors for the remaining 15 cores
- * The slot descriptor is:
- * u32 res_id;
- * u32 type;
- * u32 vma;
- *
- * Log buffer slots have the following layout:
+ * Log buffer debug window slots have the following layout:
  * u32 host_read_ptr;
  * u32 dsp_write_ptr;
  * u8 buffer[];

sound/soc/sof/ipc4.c

@@ -586,11 +586,16 @@ size_t sof_ipc4_find_debug_slot_offset_by_type(struct snd_sof_dev *sdev,
 
 	/* The type is the second u32 in the slot descriptor */
 	slot_desc_type_offset = sdev->debug_box.offset + sizeof(u32);
-	for (i = 0; i < SOF_IPC4_MAX_DEBUG_SLOTS; i++) {
+	for (i = 0; i < SOF_IPC4_MAX_DEBUG_DESCS; i++) {
 		sof_mailbox_read(sdev, slot_desc_type_offset, &type, sizeof(type));
 
-		if (type == slot_type)
+		if (type == slot_type) {
+			if (i == SOF_IPC4_MAX_DEBUG_DESCS - 1)
+				/* Desc 15: see comment on SOF_IPC4_MAX_DEBUG_DESCS in header.h */
+				return sdev->debug_box.offset + SOF_IPC4_DEBUG_PAGE0_SLOT_OFFSET;
+
 			return sdev->debug_box.offset + (i + 1) * SOF_IPC4_DEBUG_SLOT_SIZE;
+		}
 
 		slot_desc_type_offset += SOF_IPC4_DEBUG_DESCRIPTOR_SIZE;
 	}