Normally the driver accesses both the RX and the TX port registers via a
paging mechanism: one register is used to select the page (i.e. the
port), which dictates the port used when accessing the port specific
registers.

The downside to this is that while debugging it's almost impossible to
access the port specific registers from the userspace, as the driver can
change the page at any moment.

The hardware supports another access mechanism: using the I2C_RX_ID
registers (one for each RX port), i2c addresses can be chosen which,
when accessed, will always use the specific port's registers, skipping
the paging mechanism.

The support is only for the RX port, but it has proven very handy while
debugging and testing. So let's add the code for this, but hide it
behind a disabled define.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 drivers/media/i2c/ds90ub960.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/media/i2c/ds90ub960.c b/drivers/media/i2c/ds90ub960.c
index 98d815526341..03938def6ae9 100644
--- a/drivers/media/i2c/ds90ub960.c
+++ b/drivers/media/i2c/ds90ub960.c
@@ -55,6 +55,15 @@
 
 #define MHZ(v) ((u32)((v) * 1000000U))
 
+/*
+ * If this is defined, the i2c addresses from UB960_DEBUG_I2C_RX_ID to
+ * UB960_DEBUG_I2C_RX_ID + 3 can be used to access the paged RX port registers
+ * directly.
+ *
+ * Only for debug purposes.
+ */
+/* #define UB960_DEBUG_I2C_RX_ID	0x40 */
+
 #define UB960_POLL_TIME_MS	500
 
 #define UB960_MAX_RX_NPORTS	4
@@ -351,7 +360,7 @@
 #define UB960_SR_FPD3_RX_ID(n)			(0xf0 + (n))
 #define UB960_SR_FPD3_RX_ID_LEN			6
 
-#define UB960_SR_I2C_RX_ID(n)			(0xf8 + (n)) /* < UB960_FPD_RX_NPORTS */
+#define UB960_SR_I2C_RX_ID(n)			(0xf8 + (n))
 
 #define UB9702_SR_REFCLK_FREQ			0x3d
 
@@ -4001,6 +4010,12 @@ static int ub960_probe(struct i2c_client *client)
 	schedule_delayed_work(&priv->poll_work,
 			      msecs_to_jiffies(UB960_POLL_TIME_MS));
 
+#ifdef UB960_DEBUG_I2C_RX_ID
+	for (unsigned int i = 0; i < 4; i++)
+		ub960_write(priv, UB960_SR_I2C_RX_ID(i),
+			    (UB960_DEBUG_I2C_RX_ID + i) << 1);
+#endif
+
 	return 0;
 
 err_free_sers:

-- 
2.43.0