Re: [PATCH 1/4] dt-bindings: clock: qcom: Add common PLL clock controller for IPQ SoC

[Jie Luo <quic_luoj@quicinc.com>]

On 8/8/2024 10:38 PM, Krzysztof Kozlowski wrote:
> On 08/08/2024 16:03, Luo Jie wrote:
>> The common PLL controller provides clocks to networking hardware
>> blocks on Qualcomm IPQ SoC. It receives input clock from the on-chip
>> Wi-Fi, and produces output clocks at fixed rates. These output rates
>> are predetermined, and are unrelated to the input clock rate. The
>> output clocks are supplied to the Ethernet hardware such as PPE
>> (packet process engine) and the externally connected switch or PHY
>> device.
>>
>> The common PLL driver is initially being supported for IPQ9574 SoC.
> 
> Drop references to driver and explain the hardware.
> 
> Above with the usage of "common" looks like this is all for some common
> driver, not for particular hardware.

Understand, will remove this driver reference.

> 
>>
>> Signed-off-by: Luo Jie <quic_luoj@quicinc.com>
>> ---
>>   .../bindings/clock/qcom,ipq-cmn-pll.yaml           | 87 ++++++++++++++++++++++
>>   1 file changed, 87 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/clock/qcom,ipq-cmn-pll.yaml b/Documentation/devicetree/bindings/clock/qcom,ipq-cmn-pll.yaml
>> new file mode 100644
>> index 000000000000..c45b3a201751
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/clock/qcom,ipq-cmn-pll.yaml
> 
> Use compatible as filename.

OK.

> 
>> @@ -0,0 +1,87 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/clock/qcom,ipq-cmn-pll.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Qualcomm Common PLL Clock Controller on IPQ SoC
>> +
>> +maintainers:
>> +  - Bjorn Andersson <andersson@kernel.org>
>> +  - Luo Jie <quic_luoj@quicinc.com>
>> +
>> +description:
>> +  The common PLL clock controller expects a reference input clock.
>> +  This reference clock is from the on-board Wi-Fi. The CMN PLL
>> +  supplies a number of fixed rate output clocks to the Ethernet
>> +  devices including PPE (packet process engine) and the connected
>> +  switch or PHY device.
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - qcom,ipq9574-cmn-pll
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  clocks:
>> +    items:
>> +      - description: The reference clock, the supported clock rates include
>> +          25000000, 31250000, 40000000, 48000000, 50000000 and 96000000 HZ.
>> +      - description: The AHB clock
>> +      - description: The SYS clock
>> +    description:
>> +      The reference clock is the source clock of CMN PLL, which is from the
>> +      Wi-Fi. The AHB and SYS clocks must be enabled to access common PLL
>> +      clock registers.
>> +
>> +  clock-names:
>> +    items:
>> +      - const: ref
>> +      - const: ahb
>> +      - const: sys
>> +
>> +  clock-output-names:
>> +    items:
>> +      - const: ppe-353mhz
>> +      - const: eth0-50mhz
>> +      - const: eth1-50mhz
>> +      - const: eth2-50mhz
>> +      - const: eth-25mhz
> 
> Drop entire property. If the names are fixed, what's the point of having
> it in DTS? There is no.

We had added the output names here for the reasons below. Can you please
let us know your suggestion whether keeping these here is fine?

1.) These output clocks are used as input reference clocks to other
consumer blocks. For example, an on-board Ethernet PHY device may be
wired to receive a specific clock from the above output clocks as
reference clock input, and hence the PHY's DTS node would need to
reference a particular index in this output clock array.

Without these output clocks being made available in this DTS, the PHY
driver in above case would not know the clock specifier to access the
handle for the desired input clock.

2.) One of the suggestions from the internal code review with Linaro was
to name the output clocks specifically based on rate and destination
(Ex: 'ppe-353mhz' for fixed rate 353 MHZ output clock connected to
Packet Process Engine block), so that the dt-bindings describe the
input/output clocks clearly.

> 
> Best regards,
> Krzysztof
>