On Friday 26 February 2016 16:34:59 Carlo Caione wrote: > On Fri, Feb 19, 2016 at 1:54 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > <cut> > > > This still really sounds like a mixed bag to me, which should better get represented > > as a syscon node, except that there are also some more structured areas in > > CBUS. > > > > Having just the registers between METAL_REVISION and HW_REV in a syscon > > is clearly wrong, as that would include the pinctrl area that already has > > a driver, but would not include some other parts that want the syscon. > > > > Maybe the best way is to make it compatible with both syscon and > > simple-bus and put the other nodes underneath. That is still rather > > ugly, but at least it works and can be extended. > > More on this topic. > > On the meson platforms (at least on the meson8 / meson8b) we have two > buses: cbus and aobus. Since in cbus we have a bunch of scattered > registers, Arnd suggested to make it compatible with both syscon and > simple-bus. So my idea was actually to update the meson8b DTSI file > adding the two buses to make it closer to the actual hardware. > > In the most simple cases moving the devices under the correct bus is a > trivial operation since (of course) the same driver can be used when > the device is attached to a different bus, like in the uart_AO case > (http://lxr.free-electrons.com/source/arch/arm/boot/dts/meson8b.dtsi#L114). > > Unfortunately pinctrl is a different beast since it requires > (http://lxr.free-electrons.com/source/drivers/pinctrl/meson/pinctrl-meson.c#L659) > at least two subnodes: one accessing registers from aobus, and the > other one from cbus. > > I know this is quite a peculiar case but I'm wondering what is the > best way to approach this issue. > > 1) We could move only the pinctrl device outside both aobus and cbus > but IMO this is ugly (at this point is probably better not having the > two buses at all described in the DTS). > 2) The second option is just to fix the driver so that the two > subnodes are not strictly required. The problem with this second > solution is that in the driver we still need to access some data > (http://lxr.free-electrons.com/source/drivers/pinctrl/meson/pinctrl-meson8b.c#L873) > that is specific to each bus. So we will end up having two different > compatibles for the two buses (meson8b-pinctrl-aobus using data from > 'ao-bank', and meson8b-pinctrl-cbus using data from 'banks'). > 3) Another option is just to have the driver with a unique compatible > poking the parent node (or just to another property) to determine on > which bus it is so that it can use the correct bus-specific data. > > Any idea / feedback? Would it be possible to split the pin controller driver into two drivers that each only access registers on one of the buses? Is that a split that makes sense from the point of view of that driver? Arnd -- 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
