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

Matthias Brugger
2019-07-04T09:08:46Z

Hi CK-Hu,

On 01/07/2019 05:55, CK Hu wrote:
> Hi, Matthias:
>
> On Fri, 2018-11-30 at 16:59 +0800, Matthias Brugger wrote:
>>
>> 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@gmail.com> wrote:
>>>>>>> On 11/17/18 12:15 AM, Rob Herring wrote:
>>>>>>>> On Fri, Nov 16, 2018 at 01:54:45PM +0100, matthias.bgg@kernel.org 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.
>
> This series have been pending for half an year, would you keep going on
> this series? If you're busy, I could complete this series, but I need to
> know what you have plan to do.
>

You are right, it took far too long for me to respond with a new version of the
series. The problem I face is, that I use my mt8173 based chromebook for
testing. It needs some downstream patches and broke somewhere between my last
email and a few month ago. I wasn't able to get serial console to work, which
made things even more complicated. Anyway, long story short, I got sidetracked
with other stuff and didn't send a new version.

If you have time to work on this, I'd happy to see things being pushed forward
by you :)

> I guess that 1/12 ~ 5/12 is for MT2701/MT8173 and that patches meet this
> discussion. 6/12 ~ 12/12 is for MT2712/MT6797 but that patches does not
> meet this discussion. So the unfinished work is to make MT2712/MT6797 to
> align MT2701/MT8173, is this right?

After re-reading the emails I think the missing part is, to probe the clocks
from the DRM driver instead of adding a new devicetree binding for them.

Regards,
Matthias

>
> Regards,
> CK
>
>>
>> Regards,
>> Matthias
>>
>>>>
>>>> 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.
>>>
>>>
>>
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>
>