Re: [PATCH v2 1/4] usb: dwc3: Add property snps,refclk-period-ns

[Thinh Nguyen <thinh.nguyen@synopsys.com>]

Hi,

On 12/21/2018 9:12 AM, Rob Herring wrote:
> On Thu, Dec 20, 2018 at 6:22 PM Thinh Nguyen <thinh.nguyen@synopsys.com> wrote:
>> Hi,
>>
>> On 12/19/2018 10:48 PM, Felipe Balbi wrote:
>>> Hi,
>>>
>>> Thinh Nguyen <thinh.nguyen@synopsys.com> writes:
>>>>>> On 12/18/2018 8:39 AM, Rob Herring wrote:
>>>>>>> On Fri, Dec 07, 2018 at 06:27:30PM -0800, Thinh Nguyen wrote:
>>>>>>>> This patch introduces property "snps,refclk-period-ns" to inform the
>>>>>>>> controller of the reference clock period. If the reference clock period
>>>>>>>> is different from the default Core Consultant setting, then this
>>>>>>>> property can be set to the reference clock period.
>>>>>>>>
>>>>>>>> This property does not control the reference clock rate. The controller
>>>>>>>> uses this value to perform internal timing calculations that are based
>>>>>>>> on the reference clock.
>>>>>>>>
>>>>>>>> Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
>>>>>>>> ---
>>>>>>>> Changes in v2:
>>>>>>>> - Split from "usb: dwc3: Add reference clock properties"
>>>>>>>> - Revise commit message and property description
>>>>>>>>
>>>>>>>>  Documentation/devicetree/bindings/usb/dwc3.txt | 2 ++
>>>>>>>>  1 file changed, 2 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>>> index 8e5265e9f658..b7e67edff9b2 100644
>>>>>>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>>>>>> @@ -99,6 +99,8 @@ 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: if set, this value informs the controller of the
>>>>>>>> +                    reference clock period in nanoseconds.
>>>>>>> Shouldn't you be able to retrieve the refclk frequency and then
>>>>>>> calculate the period?
>>>>>> The thing is we cannot determine the ref_clk frequency for some devices
>>>>>> that don't specify their clocks. So I think we should have an option to
>>>>>> inform the controller of the ref_clk period for those devices.
>>>>> Specifying the clock should be mandatory (if you want/need this
>>>>> feature). It just requires a fixed-clock node at a minimum.
>>>> Depending on the design of the controller, the ref_clk frequency is not
>>>> something that the OS can read/control. So we cannot make it mandatory
>>>> for every device to have a clock node.
>>> We can make it mandatory to everyone who wants to use the feature. It's
>>> no different than making snps,refclk-period-ns mandatory to everyone who
>>> wants to use the feature you're introducing.
>>>
>> But not every design has access to the clock with an actual address for
>> the OS to read. Only the developers will know the frequency of the
>> ref_clk, and they can inform the controller via this property.
> Then you use the flxed-clock binding.

Ah.. I didn't know that. Sure, I'll check and revise the change so it
can be done that way.

Thanks,
Thinh