Re: [PATCH v5 1/7] dt-bindings: display: verisilicon,dc: generalize for single-output variants

[Joey Lu <a0987203069@gmail.com>]

On 6/29/2026 11:02 PM, Conor Dooley wrote:
> On Mon, Jun 29, 2026 at 01:31:46PM +0800, Icenowy Zheng wrote:
>>>>>>>>>> +
>>>>>>>>>> +        resets:
>>>>>>>>>> +          minItems: 1
>>>>>>>>>> +          maxItems: 1
>>>>>>>>>> +
>>>>>>>>>> +        reset-names:
>>>>>>>>>> +          items:
>>>>>>>>>> +            - const: core
>>>>>>>>> This is just maxItems: 1.
>>>>>>>> Well the implicit rules of DT binding schemas are quite
>>>>>>>> weird...
>>>>>>> I don't think it is that strange, as the binding has
>>>>>>>     reset-names:
>>>>>>>       items:
>>>>>>>         - const: core
>>>>>>>         - const: axi
>>>>>>>         - const: ahb
>>>>>> Ah does the list constraint the order of items? If it
>>>>>> constrains
>>>>>> the
>>>>> It does, yes.
>>>>> Alternatively, using an enum permits free ordering.
>>>> Ah in this case this should be converted to an enum, I think.
>>>>
>>>> Should I send a patch for converting it?
>>>>
>>>> Thanks,
>>>> Icenowy
>>> Thank you all for the detailed review and discussion, it really
>>> helped
>>> clarify the right approach.
>>>
>>> Since I will supply all four clocks with the same phandle for
>>> core/axi/ahb,
>>> and only one reset "core" for MA35D1, the ordering constraint in the
>>> `items` list is not a problem, "core" is already the first entry.
>>> There
>>> is no need to convert to an enum.
>>>
>>> Regarding the clock situation for the MA35D1: I agree with supplying
>>> all
>>> four clocks (core, axi, ahb, pix0) in the devicetree, even though the
>>> MA35D1 clock controller gates core/axi/ahb with a single bit. The DT
>>> will
>>> use the same clock phandle for core, axi, and ahb:
>>>
>>>     clocks = <&clk X>, <&clk X>, <&clk X>, <&pix_clk Y>;
>>>     clock-names = "core", "axi", "ahb", "pix0";
>>>
>>> This correctly models the hardware topology. Since all three names
>> No, this doesn't correctly model the hardware topology -- this will
>> lead to clk_get_rate() return the rate of DC core clock when checking
>> the AXI clock rate, which is problematic because both clocks are
>> limiting the performance of the DC.
You are right. The current MA35D1 clock driver does not correctly reflect
the real AXI/AHB clock rates, and I think it needs a more comprehensive
review and rework. I will address this in a separate clock driver patch
series in the future.

For this DRM patch series, the AXI and AHB clocks are shared system bus
clocks fixed by the SoC clock tree and are not managed by the display
driver. The driver does not query their frequencies for mode validation
or bandwidth decisions. Therefore, driver correctness is independent of
the reported AXI/AHB clock rates, meaning it will remain unaffected when
the clock driver is later reworked.
>>> resolve
>>> to the same underlying clock node, the CCF's standard enable
>>> refcounting
>>> handles the shared gate correctly without any custom implementation
>>> needed.
>>> I will also revert the change in patch 4/7 that made axi and ahb
>>> clocks
>>> optional, since they will now always be provided in the devicetree.
>>>
>>> Regarding moving `resets` and `reset-names` to the top-level
>>> `required:`,
>>> I will wait for Icenowy's patch to land before sending v6 to avoid
>>> duplicating the work.
>> The patch is sent.
Got it.
>>> In v6 I will update patch 1/7 with:
>>> - Update the subject to "dt-bindings: display: verisilicon,dc: add
>>>     support for nuvoton,ma35d1-dcu"
>>> - Lower `clocks`/`clock-names` `minItems` to 4 at the top level
>>> - Remove the `thead,th1520-dc8200` conditional block entirely
>> I think this conditional block will still be needed, because it will
>> need to constrain the minItems to ensure all clocks / resets are
>> populated.
> Correct. When the outer constraints are relaxed to deal with the new
> device the conditional block for the th1520 becomes required. Or having
> an else, but if all devices are likely to be different in terms of
> configuration specific conditional blocks is better.
Understood. I will keep the `thead,th1520-dc8200` conditional block.