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

Hector Martin
2021-02-10T13:03:16Z

On 10/02/2021 21.24, Daniel Palmer wrote:
> 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.

So far the answer seems to be to take the best guess available, and then
we get to fix it until we have real users and breaking DT compatibility
is no longer an option... :-)

>> 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.

In our case it's an existing driver (with patches) that is already
integrated with the clock infrastructure, so it makes sense to use a
fixed-clock instead of just an ad-hoc property.

--
Hector Martin (marcan@marcan.st)
Public Key: https://mrcn.st/pub