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. Rob
