regmap: Add hook for printk logging for debugging during early init

Sometimes for failures during very early init the trace infrastructure
isn't available early enough to be used.  For this sort of problem
defining LOG_DEVICE will add printks for basic register I/O on a specific
device, allowing trace to be extracted when the trace system doesn't come
up early enough to work with.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap.c

@@ -21,6 +21,18 @@
 
 #include "internal.h"
 
+/*
+ * Sometimes for failures during very early init the trace
+ * infrastructure isn't available early enough to be used.  For this
+ * sort of problem defining LOG_DEVICE will add printks for basic
+ * register I/O on a specific device.
+ */
+#undef LOG_DEVICE
+
+static int _regmap_update_bits(struct regmap *map, unsigned int reg,
+			       unsigned int mask, unsigned int val,
+			       bool *change);
+
 bool regmap_writeable(struct regmap *map, unsigned int reg)
 {
 	if (map->max_register && reg > map->max_register)
@@ -700,6 +712,11 @@ int _regmap_write(struct regmap *map, unsigned int reg,
 		}
 	}
 
+#ifdef LOG_DEVICE
+	if (strcmp(dev_name(map->dev), LOG_DEVICE) == 0)
+		dev_info(map->dev, "%x <= %x\n", reg, val);
+#endif
+
 	trace_regmap_reg_write(map->dev, reg, val);
 
 	if (map->format.format_write) {
@@ -903,6 +920,12 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
 	ret = _regmap_raw_read(map, reg, map->work_buf, map->format.val_bytes);
 	if (ret == 0) {
 		*val = map->format.parse_val(map->work_buf);
+
+#ifdef LOG_DEVICE
+		if (strcmp(dev_name(map->dev), LOG_DEVICE) == 0)
+			dev_info(map->dev, "%x => %x\n", reg, *val);
+#endif
+
 		trace_regmap_reg_read(map->dev, reg, *val);
 	}