[PATCH v2 3/3] ASoC: wm8940: Read chip ID when wm8940 codec probing

[Lukasz Majewski <lukma@denx.de>]

The wm8940 provides the chip ID information via I2C. In this
patch this information is read and if not matching expected
value, the probe function is aborted.

This prevents from using (i.e. inserting) other wm89* modules
which use the same I2C bus address.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
Changes for v2:
- None
---
 sound/soc/codecs/wm8940.c | 11 +++++++++++
 sound/soc/codecs/wm8940.h |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/sound/soc/codecs/wm8940.c b/sound/soc/codecs/wm8940.c
index 1b02d5e8a007..8eb4782c9232 100644
--- a/sound/soc/codecs/wm8940.c
+++ b/sound/soc/codecs/wm8940.c
@@ -760,6 +760,17 @@ static int wm8940_probe(struct snd_soc_component *component)
 	int ret;
 	u16 reg;
 
+	/*
+	 * Check chip ID for wm8940 - value of 0x00 offset
+	 * SOFTWARE_RESET on write
+	 * CHIP_ID on read
+	 */
+	reg = snd_soc_component_read(component, WM8940_SOFTRESET);
+	if (reg != WM8940_CHIP_ID) {
+		dev_err(component->dev, "Wrong wm8940 chip ID: 0x%x\n", reg);
+		return -ENODEV;
+	}
+
 	ret = wm8940_reset(component);
 	if (ret < 0) {
 		dev_err(component->dev, "Failed to issue reset\n");
diff --git a/sound/soc/codecs/wm8940.h b/sound/soc/codecs/wm8940.h
index 0d4f53ada2e6..86bbf902ef5a 100644
--- a/sound/soc/codecs/wm8940.h
+++ b/sound/soc/codecs/wm8940.h
@@ -95,5 +95,8 @@ struct wm8940_setup_data {
 #define WM8940_OPCLKDIV_3 2
 #define WM8940_OPCLKDIV_4 3
 
+/* Chip ID */
+#define WM8940_CHIP_ID 0x8940
+
 #endif /* _WM8940_H */
 
-- 
2.20.1