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:
>>> Add two new device properties to program the reference clock period and
>>> to enable low power management using the reference clock. This allows a
>>> higher demand to go in low power for Audio Device Class devices. This
>>> feature is currently only valid for DWC_usb31 peripheral controller
>>> v1.80a and higher.
>>>
>>> Set "snps,refclk-period-ns" 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            |
>>>  +-------------+-----------------+
>>>
>>> Set "snps,refclk-lpm" to enable low power scheduling of isochronous
>>> transfers by running SOF/ITP counters using the reference clock. Both
>>> "snps,dis_u2_susphy_quirk" and "snps,dis_enblslpm_quirk" must not be
>>> set for this feature to be enabled.
>>>
>>> Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
>>> ---
>>>  Documentation/devicetree/bindings/usb/dwc3.txt | 18 ++++++++++++++++++
>>>  1 file changed, 18 insertions(+)
>>>
>>> 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.

-- 
balbi

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