soundwire: debugfs: Switch to sdw_read_no_pm

It is rather inefficient to be constantly playing with the runtime
PM reference for each individual register, switch to holding a PM
runtime reference across the whole register output.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20221125142028.1118618-4-ckeepax@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/debugfs.c

@@ -4,6 +4,7 @@
 #include <linux/device.h>
 #include <linux/debugfs.h>
 #include <linux/mod_devicetable.h>
+#include <linux/pm_runtime.h>
 #include <linux/slab.h>
 #include <linux/soundwire/sdw.h>
 #include <linux/soundwire/sdw_registers.h>
@@ -35,7 +36,7 @@ static ssize_t sdw_sprintf(struct sdw_slave *slave,
 {
 	int value;
 
-	value = sdw_read(slave, reg);
+	value = sdw_read_no_pm(slave, reg);
 
 	if (value < 0)
 		return scnprintf(buf + pos, RD_BUF - pos, "%3x\tXX\n", reg);
@@ -55,6 +56,12 @@ static int sdw_slave_reg_show(struct seq_file *s_file, void *data)
 	if (!buf)
 		return -ENOMEM;
 
+	ret = pm_runtime_resume_and_get(&slave->dev);
+	if (ret < 0 && ret != -EACCES) {
+		kfree(buf);
+		return ret;
+	}
+
 	ret = scnprintf(buf, RD_BUF, "Register  Value\n");
 
 	/* DP0 non-banked registers */
@@ -112,6 +119,10 @@ static int sdw_slave_reg_show(struct seq_file *s_file, void *data)
 	}
 
 	seq_printf(s_file, "%s", buf);
+
+	pm_runtime_mark_last_busy(&slave->dev);
+	pm_runtime_put(&slave->dev);
+
 	kfree(buf);
 
 	return 0;