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

The debug memory window is split in 4KiB large slots. Slot 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 slot zero
after slot descriptors to be used as slot number 15, the highest
possible slot number.

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

Author: lyakh

include/sound/sof/ipc4/header.h

@@ -542,10 +542,16 @@ struct sof_ipc4_notify_resource_data {
 #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 is divided into 16 slots, and slot zero is used as a
+ * recorder for the other 15 slots.
+ * Note, that the last slot number 15 is used in a special way: so far on all
+ * ADSP platforms the debug memory window has 2 or 3 pages, i.e. it can only
+ * fit 1 or 2 slots in addition to the first slot with descriptors. But those
+ * descriptors occupy much less than 1kB of memory, so more than 3 kB of memory
+ * remain unused there. We use index 15 to point to those 3kB of memory in slot
+ * zero to be used for the GDB stub communication.
  */
-#define SOF_IPC4_MAX_DEBUG_SLOTS		15
+#define SOF_IPC4_MAX_DEBUG_SLOTS		15	   /* usable slots 1..15 */
 #define SOF_IPC4_DEBUG_SLOT_SIZE		0x1000
 
 /* debug log slot types */

sound/soc/sof/ipc4-priv.h

@@ -120,6 +120,8 @@ void sof_ipc4_update_cpc_from_manifest(struct snd_sof_dev *sdev,
 
 size_t sof_ipc4_find_debug_slot_offset_by_type(struct snd_sof_dev *sdev,
 					       u32 slot_type);
+ssize_t sof_ipc4_find_debug_slot_offset_by_index(struct snd_sof_dev *sdev,
+						 unsigned int index);
 
 void sof_ipc4_mic_privacy_state_change(struct snd_sof_dev *sdev, bool state);
 

sound/soc/sof/ipc4.c

@@ -552,6 +552,21 @@ static int sof_ipc4_init_msg_memory(struct snd_sof_dev *sdev)
 	return 0;
 }
 
+ssize_t sof_ipc4_find_debug_slot_offset_by_index(struct snd_sof_dev *sdev,
+						 unsigned int index)
+{
+	if (!index || index > SOF_IPC4_MAX_DEBUG_SLOTS)
+		return -EINVAL;
+
+	/* Slots 1..14 */
+	if (index < SOF_IPC4_MAX_DEBUG_SLOTS)
+		return sdev->debug_box.offset + index * SOF_IPC4_DEBUG_SLOT_SIZE;
+
+	/* Slot 15: see comment for SOF_IPC4_MAX_DEBUG_SLOTS in header.h */
+	return sdev->debug_box.offset + 1024;
+}
+EXPORT_SYMBOL(sof_ipc4_find_debug_slot_offset_by_index);
+
 size_t sof_ipc4_find_debug_slot_offset_by_type(struct snd_sof_dev *sdev,
 					       u32 slot_type)
 {