[PATCH v3 9/9] i2c: atr: add passthrough flag

[Cosmin Tanislav <demonsingur@gmail.com>]

Some I2C ATRs can have other I2C ATRs as children. The I2C messages of
the child ATRs need to be forwarded as-is if the parent I2C ATR can
only do static mapping.

In the case of GMSL, the deserializer I2C ATR actually doesn't have I2C
address remapping hardware capabilities, but it is able to select which
GMSL link to talk to, allowing it to change the address of the
serializer.

The child ATRs need to have their alias pools defined in such a way to
prevent overlapping addresses between them, but there's no way around
this without orchestration between multiple ATR instances.

To allow for this use-case, add a flag that allows unmapped addresses
to be passed through, since they are already remapped by the child ATRs.

There's no case where an address that has not been remapped by the child
ATR will hit the parent ATR.

Signed-off-by: Cosmin Tanislav <demonsingur@gmail.com>
---
 drivers/i2c/i2c-atr.c   | 7 +++++--
 include/linux/i2c-atr.h | 2 ++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-atr.c b/drivers/i2c/i2c-atr.c
index 699cf23185c0..c7d0a30e7c39 100644
--- a/drivers/i2c/i2c-atr.c
+++ b/drivers/i2c/i2c-atr.c
@@ -390,6 +390,9 @@ static int i2c_atr_map_msgs(struct i2c_atr_chan *chan, struct i2c_msg *msgs,
 		c2a = i2c_atr_get_mapping_by_addr(chan, msgs[i].addr);
 
 		if (!c2a) {
+			if (atr->flags & I2C_ATR_F_PASSTHROUGH)
+				continue;
+
 			dev_err(atr->dev, "client 0x%02x not mapped!\n",
 				msgs[i].addr);
 
@@ -482,13 +485,13 @@ static int i2c_atr_smbus_xfer(struct i2c_adapter *adap, u16 addr,
 
 	c2a = i2c_atr_get_mapping_by_addr(chan, addr);
 
-	if (!c2a) {
+	if (!c2a && !(atr->flags & I2C_ATR_F_PASSTHROUGH)) {
 		dev_err(atr->dev, "client 0x%02x not mapped!\n", addr);
 		mutex_unlock(&chan->alias_pairs_lock);
 		return -ENXIO;
 	}
 
-	alias = c2a->alias;
+	alias = c2a ? c2a->alias : addr;
 
 	mutex_unlock(&chan->alias_pairs_lock);
 
diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
index 7c6a9627191d..f979b931ca05 100644
--- a/include/linux/i2c-atr.h
+++ b/include/linux/i2c-atr.h
@@ -22,9 +22,11 @@ struct i2c_atr;
  * enum i2c_atr_flags - Flags for an I2C ATR driver
  *
  * @I2C_ATR_F_STATIC: ATR does not support dynamic mapping, use static mapping
+ * @I2C_ATR_F_PASSTHROUGH: Allow unmapped incoming addresses to pass through
  */
 enum i2c_atr_flags {
 	I2C_ATR_F_STATIC = BIT(0),
+	I2C_ATR_F_PASSTHROUGH = BIT(1),
 };
 
 /**
-- 
2.48.1