Hello Arnd, On 10/06/2014 16:47, Arnd Bergmann wrote: > On Tuesday 10 June 2014 16:36:04 Maxime Ripard wrote: >> On Tue, Jun 10, 2014 at 03:54:56PM +0200, Arnd Bergmann wrote: >>> On Tuesday 10 June 2014 15:47:16 Boris BREZILLON wrote: >>>> +config I2C_SUN6I_P2WI >>>> + tristate "Allwinner sun6i internal P2WI controller" >>>> + depends on ARCH_SUNXI >>>> + help >>>> + If you say yes to this option, support will be included for the >>>> + P2WI (Push/Pull 2 Wire Interface) controller embedded in some sunxi >>>> + SOCs. >>>> + The P2WI looks like an SMBus controller (which supports only byte >>>> + accesses), except that it only supports one slave device. >>>> + This interface is used to connect to specific PMIC devices (like the >>>> + AXP221). >>>> + >>> Sorry for the stupid question, but why is this an i2c driver if the >>> hardware protocol is completely different? >> It's not completely different. It deviates, but still looks very >> similar to i2c, and to be precise, SMBus. >> >> You'll have the full discussion that led to do this in i2c here: >> http://www.spinics.net/lists/linux-i2c/msg15066.html >> >> Also, one significant thing to take into account is that the >> communication with a device starts as I2C, only to switch to this >> protocol after some initialization sequence. > Ok, sounds good. > >>> I understand that a lot of devices can be driven using either spi or >>> i2c, and we have two sets of {directories,maintainers,bus_types,...} >>> for them. Your description sounds like this is a separate option >>> that isn't any closer to i2c than it is to spi. >> That's not true. It's *much* closer from I2C than it is from SPI. > Ok. > >>> Would it perhaps be better to expose it only as a regmap rather than >>> an i2c host? >> That could be a solution, but is it a common practice to define a bus >> adapter driver in a regmap driver? > No, not yet. > > Maybe Boris can just put an explanation into the changeset description > of the driver so other people are able to find it more easily. You mean in my commit message ? I thought it was already explaining the subtle differences between P2WI and the SMBus protocols. What would you like me to add to this explanation ? Something about the I2C to P2WI initialization part ? Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
