Hi, On 12/21/2018 9:12 AM, Rob Herring wrote: > On Thu, Dec 20, 2018 at 6:22 PM Thinh Nguyen <thinh.nguyen@xxxxxxxxxxxx> wrote: >> Hi, >> >> On 12/19/2018 10:48 PM, Felipe Balbi wrote: >>> 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. >>> >> 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
