Hi Rob, On 12/19/2018 5:18 AM, Rob Herring wrote: > On Tue, Dec 18, 2018 at 6:22 PM Thinh Nguyen <thinh.nguyen@xxxxxxxxxxxx> wrote: >> Hi Rob, >> >> 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. Thinh
