Messages in this thread | | | Date | Wed, 4 Mar 2015 17:39:35 +0100 | From | Maxime Ripard <> | Subject | Re: [PATCH v2 2/4] i2c: sunxi: Add Reduced Serial Bus (RSB) DT bindings documentation |
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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
-- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com [unhandled content-type:application/pgp-signature] | |