soc: ti: wkup_m3_ipc: Add debug option to halt m3 in suspend

Add a debugfs option to allow configurable halting of the wkup_m3
during suspend at the last possible point before low power mode entry.
This condition can only be resolved through JTAG and advancing beyond
the while loop in a8_lp_ds0_handler [1]. Although this hangs the system
it forces the system to remain active once it has been entirely
configured for low power mode entry, allowing for register inspection
through JTAG to help in debugging transition errors.

Halt mode can be set using the enable_off_mode entry under wkup_m3_ipc
in the debugfs.

[1] https://git.ti.com/cgit/processor-firmware/ti-amx3-cm3-pm-firmware/tree/src/pm_services/pm_handlers.c?h=08.02.00.006#n141

Suggested-by: Brad Griffis <bgriffis@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
[dfustini: add link for a8_lp_ds0_handler() in ti-amx3-cm3-pm-firmware]
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20220502033211.1383158-1-dfustini@baylibre.com

drivers/soc/ti/wkup_m3_ipc.c

@@ -7,6 +7,7 @@
  * Dave Gerlach <d-gerlach@ti.com>
  */
 
+#include <linux/debugfs.h>
 #include <linux/err.h>
 #include <linux/firmware.h>
 #include <linux/kernel.h>
@@ -50,6 +51,9 @@
 #define IPC_IO_ISOLATION_STAT_SHIFT	(10)
 #define IPC_IO_ISOLATION_STAT_MASK	(0x1 << 10)
 
+#define IPC_DBG_HALT_SHIFT		(11)
+#define IPC_DBG_HALT_MASK		(0x1 << 11)
+
 #define M3_STATE_UNKNOWN		0
 #define M3_STATE_RESET			1
 #define M3_STATE_INITED			2
@@ -157,6 +161,73 @@ static int wkup_m3_init_scale_data(struct wkup_m3_ipc *m3_ipc,
 	return ret;
 }
 
+#ifdef CONFIG_DEBUG_FS
+static void wkup_m3_set_halt_late(bool enabled)
+{
+	if (enabled)
+		m3_ipc_state->halt = (1 << IPC_DBG_HALT_SHIFT);
+	else
+		m3_ipc_state->halt = 0;
+}
+
+static int option_get(void *data, u64 *val)
+{
+	u32 *option = data;
+
+	*val = *option;
+
+	return 0;
+}
+
+static int option_set(void *data, u64 val)
+{
+	u32 *option = data;
+
+	*option = val;
+
+	if (option == &m3_ipc_state->halt) {
+		if (val)
+			wkup_m3_set_halt_late(true);
+		else
+			wkup_m3_set_halt_late(false);
+	}
+
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(wkup_m3_ipc_option_fops, option_get, option_set,
+			"%llu\n");
+
+static int wkup_m3_ipc_dbg_init(struct wkup_m3_ipc *m3_ipc)
+{
+	m3_ipc->dbg_path = debugfs_create_dir("wkup_m3_ipc", NULL);
+
+	if (!m3_ipc->dbg_path)
+		return -EINVAL;
+
+	(void)debugfs_create_file("enable_late_halt", 0644,
+				  m3_ipc->dbg_path,
+				  &m3_ipc->halt,
+				  &wkup_m3_ipc_option_fops);
+
+	return 0;
+}
+
+static inline void wkup_m3_ipc_dbg_destroy(struct wkup_m3_ipc *m3_ipc)
+{
+	debugfs_remove_recursive(m3_ipc->dbg_path);
+}
+#else
+static inline int wkup_m3_ipc_dbg_init(struct wkup_m3_ipc *m3_ipc)
+{
+	return 0;
+}
+
+static inline void wkup_m3_ipc_dbg_destroy(struct wkup_m3_ipc *m3_ipc)
+{
+}
+#endif /* CONFIG_DEBUG_FS */
+
 static void am33xx_txev_eoi(struct wkup_m3_ipc *m3_ipc)
 {
 	writel(AM33XX_M3_TXEV_ACK,
@@ -402,7 +473,9 @@ static int wkup_m3_prepare_low_power(struct wkup_m3_ipc *m3_ipc, int state)
 	wkup_m3_ctrl_ipc_write(m3_ipc, m3_power_state, 1);
 	wkup_m3_ctrl_ipc_write(m3_ipc, m3_ipc->mem_type |
 			       m3_ipc->vtt_conf |
-			       m3_ipc->isolation_conf, 4);
+			       m3_ipc->isolation_conf |
+			       m3_ipc->halt, 4);
+
 	wkup_m3_ctrl_ipc_write(m3_ipc, DS_IPC_DEFAULT, 2);
 	wkup_m3_ctrl_ipc_write(m3_ipc, DS_IPC_DEFAULT, 3);
 	wkup_m3_ctrl_ipc_write(m3_ipc, DS_IPC_DEFAULT, 6);
@@ -631,6 +704,8 @@ static int wkup_m3_ipc_probe(struct platform_device *pdev)
 		goto err_put_rproc;
 	}
 
+	wkup_m3_ipc_dbg_init(m3_ipc);
+
 	return 0;
 
 err_put_rproc:
@@ -642,6 +717,8 @@ err_free_mbox:
 
 static int wkup_m3_ipc_remove(struct platform_device *pdev)
 {
+	wkup_m3_ipc_dbg_destroy(m3_ipc_state);
+
 	mbox_free_channel(m3_ipc_state->mbox);
 
 	rproc_shutdown(m3_ipc_state->rproc);

include/linux/wkup_m3_ipc.h

@@ -36,6 +36,7 @@ struct wkup_m3_ipc {
 	int vtt_conf;
 	int isolation_conf;
 	int state;
+	u32 halt;
 
 	unsigned long volt_scale_offsets;
 	const char *sd_fw_name;
@@ -46,6 +47,7 @@ struct wkup_m3_ipc {
 
 	struct wkup_m3_ipc_ops *ops;
 	int is_rtc_only;
+	struct dentry *dbg_path;
 };
 
 struct wkup_m3_wakeup_src {