[PATCH v2 2/4] i2c: sunxi: Add Reduced Serial Bus (RSB) DT bindings documentation

Maxime Ripard maxime.ripard at free-electrons.com
Wed Mar 4 08:39:35 PST 2015

On Mon, Mar 02, 2015 at 04:24:44PM +0800, Chen-Yu Tsai wrote:
> Reduced Serial Bus (RSB) is an SMBus like bus used to communicate
> with some PMICs (like the AXP223) or other peripherals.
> The RSB DT bindings are pretty much the same as the one defined for
> the marvell's mv64xxx controller, with the additional RSB specific
> "allwinner,rsb-hw-addr" property for slave device nodes.
> There are 2 types of addresses for RSB devices, a hardware address
> and a runtime (software) configurable address. The former is only
> used when configuring the latter. All read/write accesses use the
> runtime address.
> It would seem straightforward to use the hardware address in the
> DT bindings as the slave's address. However this will not work as
> the hardware address is 12 bits wide, and at least 1 device, the
> AC100 audio codec, has the highest bit set. This address would be
> incompatible with I2C (7 or 10 bit addresses) and likely rejected.
> Hence this binding uses statically allocated (by the author of the
> DT) runtime addresses for the slave's "reg" property. The hardware
> address is put in a separete named property. When writing a new DT,
                      ^ separate
> the author must take care to not have multiple slave devices use
> the same address. It is recommended to follow whatever conventions
> the hardware vendor uses.

While very complete, the three last paragraphs should rather be, or at
least duplicated, in the file itself.


Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
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