i2c: Support dynamic address translation

The i2c-atr module keeps a list of associations between I2C client aliases
and I2C addresses. This represents the address translation table which is
programmed into an ATR channel at any given time. This list is only updated
when a new client is bound to the channel.

However in some cases, an ATR channel can have more downstream clients than
available aliases. One example of this is an SFP module that is bound to an
FPC202 port. The FPC202 port can only access up to two logical I2C
addresses. However, the SFP module may expose up to three logical I2C
addresses: its EEPROM on 7-bit addresses 0x50 and 0x51, and a PHY
transceiver on address 0x56.

In cases like these, it is necessary to reconfigure the channel's
translation table on the fly, so that all three I2C addresses can be
accessed when needed.

As there are currently no known ATR's which do not support dynamic address
translation, this feature can be enabled by default without breaking
existing use cases.

Modify the i2c-atr module to provide on-the-fly address translation. This
is achieved by modifying an ATR channel's translation table whenever an I2C
transaction with unmapped clients is requested.

Add a mutex to protect alias_list. This prevents
i2c_atr_dynamic_attach/detach_addr from racing with the bus notifier
handler to modify alias_list.

Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Acked-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

0 files changed, 0 insertions, 0 deletions