Hi, Thinh Nguyen <thinh.nguyen@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> >>>>> --- >>>>> 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. -- balbi
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