Hi I2C Enthusiasts,
I'm starting to look at supporting the I2C controller on the Realtek
RTL9300 and I'm struggling a little bit to figure out how to represent
it. It's a bit odd in that there are basically two I2C controllers which
have a SCL pin each but then there are 8 common SDA pins that can be
split between the two controllers to give a level of muxing and/or
concurrency.
Basically I can have: SDA[0:7] + SCL8 or SDA[0:7] + SCL17 or any of the
possible permutations. I could be accessing SDA0+SCL8 and SCL1+SDA17
concurrently but if the hardware were connected as SDA0+SCL8 and
SCL1+SDA8 I'd have to make those mutually exclusive.
I think it might just make sense to represent the two entities that own
the SCL pins as separate controllers but then it'd be hard to enforce
the fact that the individual SDA pins can only belong to one controller.
Complicating things a bit further there is a common register that says
whether the pins are being used for SDA or as GPIO (that can probably
just be handled with pinctrl).
So I was thinking something like
i2c@36c {
reg = <0x36c 0x14>
compatible = "realtek,rtl9300-i2c";
scl-pin = <8>;
i2c@0 {
sda-pin = <0>; // could use reg instead of scl-pin
}
i2c@1 {
sda-pin = <1>;
}
};
i2c@388 {
reg = <0x388 0x14>
scl-pin = <17>;
compatible = "realtek,rtl9300-i2c";
i2c@2 {
sda-pin = <2>;
}
i2c@3 {
sda-pin = <3>;
}
};
Does that make sense? I'm not entirely sure how I can have those root
controllers as something the I2C framework knows about without them
being adapters in their own right (they can't have any devices attached
directly that'd need to be done on one of the channels).
There are drivers for this in openwrt[1][2] but they ignore the fact
that there are multiple controllers and the muxing is done separately. I
was planning on using them for a bit of inspiration.
[1] -
https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/realtek/files-5.15/drivers/i2c/busses/i2c-rtl9300.c
[2] -
https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/realtek/files-5.15/drivers/i2c/muxes/i2c-mux-rtl9300.c
Thanks,
Chris
