Re: [PATCH v5 08/12] dt-bindings: mediatek: Change the binding for mmsys clocks

From: Matthias Brugger
Date: Fri Nov 30 2018 - 04:00:05 EST

On 30/11/2018 07:43, Stephen Boyd wrote:
> Quoting Matthias Brugger (2018-11-21 09:09:52)
>> On 21/11/2018 17:46, Stephen Boyd wrote:
>>> Quoting Rob Herring (2018-11-19 11:15:16)
>>>> On Sun, Nov 18, 2018 at 11:12 AM Matthias Brugger
>>>> <matthias.bgg@xxxxxxxxx> wrote:
>>>>> On 11/17/18 12:15 AM, Rob Herring wrote:
>>>>>> On Fri, Nov 16, 2018 at 01:54:45PM +0100, matthias.bgg@xxxxxxxxxx wrote:
>>>>>>> - #clock-cells = <1>;
>>>>>>> +
>>>>>>> + mmsys_clk: clock-controller@14000000 {
>>>>>>> + compatible = "mediatek,mt2712-mmsys-clk";
>>>>>>> + #clock-cells = <1>;
>>>>>> This goes against the general direction of not defining separate nodes
>>>>>> for providers with no resources.
>>>>>> Why do you need this and what does it buy if you have to continue to
>>>>>> support the existing chips?
>>>>> It would show explicitly that the mmsys block is used to probe two
>>>>> drivers, one for the gpu and one for the clocks. Otherwise that is
>>>>> hidden in the drm driver code. I think it is cleaner to describe that in
>>>>> the device tree.
>>>> No, that's maybe cleaner for the driver implementation in the Linux
>>>> kernel. What about other OS's or when Linux drivers and subsystems
>>>> needs change? Cleaner for DT is design bindings that reflect the h/w.
>>>> Hardware is sometimes just messy.
>>> I agree. I fail to see what this patch series is doing besides changing
>>> driver probe and device creation methods and making a backwards
>>> incompatible change to DT. Is there any other benefit here?
>> You are referring whole series?
>> Citing the cover letter:
>> "MMSYS in Mediatek SoCs has some registers to control clock gates (which is
>> used in the clk driver) and some registers to set the routing and enable
>> the differnet (sic!) blocks of the display subsystem.
>> Up to now both drivers, clock and drm are probed with the same device tree
>> compatible. But only the first driver get probed, which in effect breaks
>> graphics on mt8173 and mt2701.
> Ouch!

Yes :)

>> This patch uses a platform device registration in the DRM driver, which
>> will trigger the probe of the corresponding clock driver. It was tested on the
>> bananapi-r2 and the Acer R13 Chromebook."
> Alright, please don't add nodes in DT just to make device drivers probe.
> Instead, register clks from the drm driver or create a child platform
> device for the clk bits purely in the drm driver and have that probe the
> associated clk driver from there.

I'll make the other SoCs probe via a child platform device from the drm driver,
as already done in 2/12 and 3/12.


>> DT is broken right now, because two drivers rely on the same node, which gets
>> consumed just once. The new DT introduced does not break anything because it is
>> only used for boards that: "[..] are not available to the general public
>> (mt2712e) or only have the mmsys clock driver part implemented (mt6797)."
> Ok, so backwards compatibility is irrelevant then. Sounds fine to me.