Re: [PATCH 02/14] dt-bindings: phy: qcom,qmp-usb3-dp: fix sc8280xp bindings

Dmitry Baryshkov
2022-11-14T15:19:34Z

On 14/11/2022 17:18, Johan Hovold wrote:
> On Mon, Nov 14, 2022 at 03:07:41PM +0100, Krzysztof Kozlowski wrote:
>> On 14/11/2022 14:27, Johan Hovold wrote:
>>> On Fri, Nov 11, 2022 at 04:17:29PM +0100, Krzysztof Kozlowski wrote:
>>>> On 11/11/2022 10:24, Johan Hovold wrote:
>>>>> The current QMP USB3-DP PHY bindings are based on the original MSM8996
>>>>> binding which provided multiple PHYs per IP block and these in turn were
>>>>> described by child nodes.
>
>>>>> + "#clock-cells":
>>>>> + const: 1
>>>>> +
>>>>> + clock-output-names:
>>>>> + items:
>>>>> + - const: usb3_pipe
>>>>> + - const: dp_link
>>>>> + - const: dp_vco_div
>>>>
>>>> Why defining here fixed names? The purpose of this field is to actually
>>>> allow customizing these - at least in most cases. If these have to be
>>>> fixed, then driver should just instantiate these clocks with such names,
>>>> right?
>>>
>>> I'm only using these names as documentation of the indexes. The driver
>>
>> What do you mean by documentation of indexes? You require these specific
>> entries and do not allow anything else.
>
> I'm using this property as documentation of the valid indexes that can
> be used when referring to clocks provided by this device.
>
> There are currently three and the mapping is described by the
> 'clock-output-names' property.
>
>>> doesn't use these names, but that's a Linux-specific implementation
>>> detail.
>>>
>>> I noticed that several bindings leave the clock indexes unspecified, or
>>> have header files defining some or all of them. I first added a QMP
>>> header but that seemed like overkill, especially if we'd end up with
>>> one header per SoC (cf. the GCC headers) due to (known and potential)
>>> platform differences.
>>
>> Headers for the names? I do not recall such but that does not seem right.
>
> Headers for the indexes.
>
>>>
>>> On the other hand reproducing this list in each node is admittedly a bit
>>> redundant.
>>>
>>> Shall I add back a shared header for all PHYs handled by this driver
>>> (another implementation detail) even if this could eventually lead to
>>> describing clocks not supported by a particular SoC (so such constraints
>>> would still need to be described by the binding somehow):
>>>
>>> /* QMP clocks */
>>> #define QMP_USB3_PIPE_CLK 0
>>> #define QMP_DP_LINK_CLK 1
>>> #define QMP_DP_VCO_DIV_CLK 2

Maybe QMP_COMBO_USB3_PIPE_CLK, QMP_COMBO_DP_LINK_CLK,
QMP_COMBO_DP_VCO_DIV_CLK?

I'll then extend this header with QMP_UFS_RX_SYMBOL_0_CLK
QMP_UFS_RX_SYMBOL_1_CLK and QMP_UFS_TX_SYMBOL_0_CLK.

>>
>> What are these about? To remind - we talk about names of clocks this
>> device creates. The output names. Whatever IDs you have are not related
>> to the names.
>
> As I mentioned above, this is not about the names that Linux gives to
> its representation of these clocks. Its just about defining the valid
> indexes in the binding.
>
> If you think that that using 'clock-output-names' for this is a bit too
> unconventional, I can add back the header with defines like the above
> instead.
>
> Note that the clock schema has:
>
> clock-output-names:
> description: |
> Recommended to be a list of strings of clock output signal
> names indexed by the first cell in the clock specifier.
> However, the meaning of clock-output-names is domain
> specific to the clock provider, ...
>
> Johan

--
With best wishes
Dmitry