Re: [PATCH 1/3] usb: dwc3: Add reference clock properties

[Felipe Balbi <balbi@kernel.org>]

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Hi,

Thinh Nguyen <thinh.nguyen@synopsys.com> writes:
>> Thinh Nguyen <thinh.nguyen@synopsys.com> writes:
>>>>>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>> index 636630fb92d7..712b344c3a31 100644
>>>>>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>> @@ -95,6 +95,24 @@ Optional properties:
>>>>>>>  			this and tx-thr-num-pkt-prd to a valid, non-zero value
>>>>>>>  			1-16 (DWC_usb31 programming guide section 1.2.3) to
>>>>>>>  			enable periodic ESS TX threshold.
>>>>>>> + - snps,refclk-period-ns: set to program the reference clock period. The valid
>>>>>>> +   			input periods are as follow:
>>>>>>> +			+-------------+-----------------+
>>>>>>> +			| Period (ns) | Freq (MHz)      |
>>>>>>> +			+-------------+-----------------+
>>>>>>> +			| 25          | 39.7/40         |
>>>>>>> +			| 41          | 24.4            |
>>>>>>> +			| 50          | 20              |
>>>>>>> +			| 52          | 19.2            |
>>>>>>> +			| 58          | 17.2            |
>>>>>>> +			| 62          | 16.1            |
>>>>>>> +			+-------------+-----------------+
>>>>>>> + - snps,enable-refclk-lpm: set to enable low power scheduling of isochronous
>>>>>>> +			transfers by running SOF/ITP counters using the
>>>>>>> +			reference clock. Only valid for DWC_usb31 peripheral
>>>>>>> +			controller v1.80a and higher. Both
>>>>>>> +			"snps,dis_u2_susphy_quirk" and
>>>>>>> +			"snps,dis_enblslpm_quirk" must not be set.
>>>>>> sounds like you should rely on clk API here. Then on driver call
>>>>>> clk_get_rate() to computer whatever you need to compute.
>>>>>>
>>>>> There's nothing to compute here. We can simply enable this feature with
>>>>> "snps, enable-refclk-lpm" and the controller will use the default refclk
>>>>> settings.
>>>> Right, right. What I'm saying, though, is that we have a clock API for
>>>> describing a clock. So why wouldn't we rely on that API for this? I
>>>> think both of these new properties can be replaced with standard clock
>>>> API properties:
>>>>
>>>> 	clocks = <&clk1>, ..., <&lpm_clk>
>>>>         clock-names = "clock1", ...., "lpm";
>>>>
>>>> Then dwc3 core could, simply, check if we have a clock named "lpm" and
>>>> if there is, use NSECS_PER_SEC / clk_get_rate() to get its period and
>>>> write it to the register that needs the information.
>>> There's no new clock here. We are using the ref_clk for SOF and ITP
>>> counter for this feature. Also, clocks are optional on non-DT platforms.
>>> To use the clock API, then we need to update the driver to allow some
>>> optional clock such as "ref" clock for non-DT platforms. Do you want to
>>> do it like this?
>> I can't think of a problem that would arise from that. Can you? Mark,
>> Rob, what do you think?
>>
> No problem. That can be done. This will remove the
> "snps,refclk-period-ns" property. But we should have
> "snps,enable-refclk-lpm" to enable this feature.

not really. Just check if you have a clock named lpm. If you do, then
you enable the feature.

-- 
balbi

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