Re: [PATCH 18/18] arm64: apple: Add initial Mac Mini 2020 (M1) devicetree

Tony Lindgren
2021-02-10T12:56:08Z

* Daniel Palmer <daniel@0x0f.com> [210210 12:24]:
> Hi Hector,
>
> On Wed, 10 Feb 2021 at 20:49, Hector Martin <marcan@marcan.st> wrote:
>
> > > Yeah, just don't use an imaginary dummy index for the reg. Use a real
> > > register offset from a clock controller instance base, and a register
> > > bit offset too if needed.
> >
> > I mean for fixed input clocks without any particular numbering, or for
> > temporary fake clocks while we figure out the clock controller. Once a
> > real clock controller is involved, if there are hardware indexes
> > involved that are consistent then of course I'll use those in some way
> > that makes sense.
>
> This exact problem exists for MStar/SigmaStar too.
> As it stands there is no documentation to show what the actual clock
> tree looks like so everything is guess and I need to come up with numbers.
> I'm interested to see what the solution to this is as it will come up again
> when mainlining chips without documentation.
>
>
> > The purpose of the clock in this particular case is just to make the
> > uart driver work, since it wants to know its reference clock; there is
> > work to be done here to figure out the real clock tree
>
> FWIW arm/boot/dts/mstar-v7.dtsi has the same issue: Needs uart,
> has no uart clock. In that instance the uart clock setup by u-boot
> is passed to the uart driver as a property instead of creating a fake
> clock.

Using more local dts nodes for the fixed clocks might help a bit with
the dummy numbering problem but is still not a nice solution.

How about using node names like "clock-foo" for the fixed clocks?
This would be along what we do for with regulator names.

Rob and Stephen might have some better suggestions here.

Regards,

Tony