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

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Hi Felipe,

On 11/8/2018 11:14 PM, Felipe Balbi wrote:
> Hi,
>
> Thinh Nguyen <thinh.nguyen@xxxxxxxxxxxx> writes:
>>> Thinh Nguyen <thinh.nguyen@xxxxxxxxxxxx> 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.
>
But this clock name should be "ref".  The new name "lpm" would make it
seem like it's a different clock.

Thinh





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