On Tue, Mar 11, 2014 at 12:00:14PM +0100, Hans de Goede wrote: > > On Tue, Mar 11, 2014 at 11:16:16AM +0100, Hans de Goede wrote: > >>> There's still some subtleties I don't get yet, but the more I > >>> think about this, the more I feel like we'll have to write our own > >>> bus :( > >> > >> So on the bus things are different then with i2c, that does not mean > >> we cannot still pretend it is i2c to upper layers in the kernel. > > > > The fact that it's not having any ACK, nor any address is kind of a > > show stopper. For all we now, we could just as much pretend it's SPI :) > > According to: > https://github.com/oliv3r/u-boot-sunxi/commit/52b8454fb8951e95da76b3d9ba82461adab5ee7f > > It does have a device address, and if I read your previous mail > correct, there is an ack.
I'm not sure about what this is actually about, but the protocol description clearly shows that there is no address sent over the bus. However, I think what happens is that it starts as an I2C bus, and that a write to this register actually switch the PMIC from I2C to P2WI mode, hence why it needs an address. And there is an ACK, but at the end of the transfer, not between each byte like on I2C. > > Plus, a lot of devices can actually be plugged onto several different > > buses, and have driver that add a small layer to access registers > > depending on which bus they're loaded from. > > > > We could very well imagine having to use regmap for the i2c part, and > > p2wi bus calls for the A31's case. > > This actually sounds like something which using a regmap would make > easier to do. Indeed. > >> And if we try and fail we can always define our own bus for this > >> later. > > > > You can still ask the i2c maintainer, but I'm afraid I know his > > answer. > > As said before I think we first need to learn more about how this > bus works before we can make a call one way or the other. What's missing from my previous mail? -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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