u-boot DT configuration node

[Rob Herring]

On Tue, Apr 28, 2020 at 8:51 AM Michal Simek <michal.simek at xilinx.com> wrote:
>
> On 28. 04. 20 15:23, Rob Herring wrote:
> > On Wed, Apr 1, 2020 at 4:23 AM Michal Simek <michal.simek at xilinx.com> wrote:
> >>
> >> Hi Rob and others,
> >>
> >> for couple of years already u-boot is using config node in root DT for
> >> u-boot configuration.
> >>
> >> Here is one example in u-boot source code.
> >> https://gitlab.denx.de/u-boot/u-boot/-/blob/master/arch/arm/dts/exynos5250-spring.dts#L47
> >>
> >> And here is dt binding description
> >> https://gitlab.denx.de/u-boot/u-boot/-/blob/master/doc/device-tree-bindings/config.txt
> >>
> >> I was checking dt binding specification and there no such a thing
> >> described there. It means I expect this is more adhoc u-boot solution.
> >> We have reached the point where could be beneficial to put some u-boot
> >> specific configurations to DT.
> >>
> >> Actually I have done similar thing some time ago too by using chosen
> >> node and add xilinx specific property there to point to eeprom.
> >> https://gitlab.denx.de/u-boot/u-boot/-/blob/master/arch/arm/dts/zynqmp-zcu102-revA.dts#L39
> >
> > In this case, I think an alias should be used as it's more of just a
> > shortcut to finding a specific node.
>
> What alias name do you suggest to use?
> We have systems where one i2c eeprom described based board and another
> i2c eeprom describe bootable module. And I need to have shotcuts to both
> of them.
>
> dt specification doesn't list any keywords for aliases but there is
> generic name recommendation.

I do want make aliases a registered list of names.

> Based on keywords it should look like this.
> eeprom0 = ...;
> eeprom1 = ...;

That was my initial thought, but maybe "nvmemX" to be a bit more generic.


> >> I think it is a time to discuss it and do it properly.
> >>
> >> First of all my question is where we could list SW prefixes to make sure
> >> that they are listed and everybody is aware about it. We have
> >> vendor-prefixes and we should have a way to record also prefixes for sw
> >> projects. U-Boot is using u-boot. Xen has file in the kernel with using
> >> xen prefix. At least these two should be listed.
> >
> > Documentation/devicetree/bindings/vendor-prefixes.yaml.
>
> thx
>
> >
> >> Next my question is what is the recommended way to pass sw specific
> >> parameters via DT? I think using chosen node is more appropriate then
> >> adhoc config node. Or is there a better way how this should be done?
> >
> > /chosen
> >
> > For vendor specific things though I would be cautious. If they are
> > settings for a specific device, then they probably belong in the
> > device's node. Second, are they really vendor specific? What we don't
> > want is each vendor doing the same thing in slightly different ways.
>
> For u-boot specific setting like - offsets it should be generic for
> everybody. I was already talking to Loic that for saving u-boot
> variables to QSPI we should be using MTD partition map and put there
> maybe a flag to say that this is the location for storing them.

I'd standardize on the partition name.

Rob