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

Hi Rob,

On 12/19/2018 5:18 AM, Rob Herring wrote:

On Tue, Dec 18, 2018 at 6:22 PM Thinh Nguyen [off-list ref] wrote:

quoted

Hi Rob,

On 12/18/2018 8:39 AM, Rob Herring wrote:

quoted

On Fri, Dec 07, 2018 at 06:27:30PM -0800, Thinh Nguyen wrote:

quoted

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 <redacted>
---
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