When we query the device let's also read the descriptor from the device.
This tells us useful information, including the version, which we use to
determine a generation.

This is based on the driver from Wacom.

Signed-off-by: Alistair Francis <redacted>
---
 drivers/input/touchscreen/wacom_i2c.c | 64 +++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/drivers/input/touchscreen/wacom_i2c.c b/drivers/input/touchscreen/wacom_i2c.c
index 28255c77d426..72ba4a36459b 100644
--- a/drivers/input/touchscreen/wacom_i2c.c
+++ b/drivers/input/touchscreen/wacom_i2c.c

@@ -16,6 +16,7 @@
 #include <linux/of.h>
 #include <asm/unaligned.h>
 
+#define WACOM_DESC_REG	0x01
 #define WACOM_CMD_QUERY0	0x04
 #define WACOM_CMD_QUERY1	0x00
 #define WACOM_CMD_QUERY2	0x33

@@ -24,11 +25,46 @@
 #define WACOM_CMD_THROW1	0x00
 #define WACOM_QUERY_SIZE	19
 
+#define WACOM_MAX_DATA_SIZE_BG9     10
+#define WACOM_MAX_DATA_SIZE_G12     15
+#define WACOM_MAX_DATA_SIZE_AG14    17
+#define WACOM_MAX_DATA_SIZE         22
+
+/* Generation selction */
+/* Before and at G9 generation */
+#define WACOM_BG9	0
+/* G12 generation the IC supports "height"*/
+#define WACOM_G12	1
+/* After and at G14 generation the IC supports "height" and
+ * it is defined as "Z" axis
+ */
+#define WACOM_AG14	2
+
+struct wacom_desc {
+	u16 descLen;
+	u16 version;
+	u16 reportLen;
+	u16 reportReg;
+	u16 inputReg;
+	u16 maxInputLen;
+	u16 outputReg;
+	u16 maxOutputLen;
+	u16 commReg;
+	u16 dataReg;
+	u16 vendorID;
+	u16 productID;
+	u16 fwVersion;
+	u16 misc_high;
+	u16 misc_low;
+};