On Wed, Jun 17, 2015 at 09:16:41AM +0200, Hans de Goede wrote:
> Hi,
> 
> On 16-06-15 19:55, Maxime Ripard wrote:
> >Hi Pantelis,
> >
> >On Sun, Jun 14, 2015 at 09:16:21PM +0300, Pantelis Antoniou wrote:
> >>>I think we need to discuss this with Pantelis and what is his feeling
> >>>about this.
> >>>
> >>>Pantelis, to sum things up, we have a case of a tablet that comes with
> >>>the exact same board, but coming in two flavours with two differents
> >>>screen resolutions. It looks like a great case for your DT quirks
> >>>work, but we have no way of runtime detecting the difference between
> >>>the two variants. What do you think about this? Should we go with
> >>>using the DT quirks or is this simply out of scope?
> >>>
> >>>There's not so much example of similar cases in the kernel, and none
> >>>of them use quirks so far (obviously) but they all boil down to either
> >>>the solution you were suggesting in that patch or adding the alternate
> >>>configuration as a comment.
> >>>
> >>>I don't think the latter would work for you, and I agree with that, so
> >>>I guess that depending on what Pantelis says, either we go with a
> >>>better solution using the quirks, or we end up using what you
> >>>suggested (with a nitpick though, I'd prefer if you used the display
> >>>standard instead of the resolution, which would make it xga I guess?)
> >>>
> >>
> >>First of all, the quirks interface is at an RFC stage (new name
> >>suggested is ‘variants’); getting that out of the way this seems
> >>like what it is designed to do.
> >>
> >>The idea of the DT quirks is to drastically cut down on the number
> >>of different DTs required, each different for each board with minute
> >>differences from one another.
> >
> >We're on the same page then :)
> >
> >>In your case you have boards that have no way to be probed about
> >>what they ‘are’, but that’s no big problem. You can easily pass the
> >>board variant in the kernel command line and use that to select the
> >>quirk to apply.
> >
> >Hans actually pointed out that this would just move the logic
> >somewhere else, but not remove it. In our case, that would mean U-Boot
> >(Hans being the U-Boot maintainer for the SoCs that are used in this
> >particular board).
> >
> >That would still require us to have a different configuration and to
> >add some logic to pass that extra parameter to the kernel. I'd be glad
> >to have less stuff in the kernel, but I can understand that he doesn't
> >want more stuff either.
> >
> >>In fact the original patchset does contain a command line quirk for
> >>enabling and disabling the onboard emmc & hdmi of the beaglebone
> >>black for capes that need to use those signals.
> >
> >Ah. I somehow overlooked that when reading it.
> >
> >>Saying that, if you’re in a hurry I’d say go with a different DTSs
> >>for now, since that’s going to go in a near kernel cycle; DT quirks
> >>will be discussed at plumber’s in a couple of months, and then we’ll
> >>if it will go in and in what form.
> >
> >Ok. I won't be here this year, but if you could raise the topic of how
> >to handle "non-discoverable boards" then, it would be great.
> >
> >Hans, I guess we can go for your suggestion then: apply a "generic" DT
> >for the board right now, we're going to need it anyway. Then, when
> >will have real display support, depending on the current state of the
> >discussion for the quirks, we will either merge a different DT
> >including the generic one, or if the quirks have something that work
> >for both of us then, use the quirks. Sounds good?
> 
> Sounds good to me, will you make the changes while merging, or shall
> I do a new version of the patch ?

I'll apply and fix.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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