On Oct 28, 2013, at 10:48 PM, Xiubo Li-B47053 wrote: >>> This adds the Document for Freescale FTM PWM driver under >>> Documentation/devicetree/bindings/pwm/. >>> >>> Signed-off-by: Xiubo Li <Li.Xiubo@xxxxxxxxxxxxx> >>> --- >>> .../devicetree/bindings/pwm/pwm-fsl-ftm.txt | 34 >> ++++++++++++++++++++++ >>> 1 file changed, 34 insertions(+) >>> create mode 100644 >>> Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt >>> >>> diff --git a/Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt >>> b/Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt >>> new file mode 100644 >>> index 0000000..175b762 >>> --- /dev/null >>> +++ b/Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt >>> @@ -0,0 +1,34 @@ >>> +Freescale FTM PWM controller >> >> What does FTM stand for, and can we spell out PWM at least once early on. >> > > "FTM" is for short of "FlexTimer Module", I'll use the full name then. > >>> + >>> +Required properties: >>> +- compatible: Should be "fsl,vf610-ftm-pwm" >>> +- reg: Physical base address and length of the controller's registers >>> +- #pwm-cells: Should be 3. See pwm.txt in this directory for a >>> +description of >>> + the cells format. >>> +- clock-names : Includes the following module clock source entries: >>> + "ftm0" (system clock), >>> + "ftm0_fix_sel" (fixed frequency clock), >>> + "ftm0_ext_sel" (external clock) >>> +- clocks : Must contain a clock specifier for each entry in >>> +clock-names, >>> + See ../clock/clock-bindings.txt for details of the property values. >>> +- fsl,pwm-counter-clk: The FTM PWM counter clock source, should be >>> +one of the >>> + entries in clock-names. >> >> Why do we need this, why not just have only the clock-names/clocks >> reference the clk that is actually used? >> > > As I have replied before, the FTM has two clock sources: the module clock and the counter clock. > > The counter clock source is selectable depends on different board and also the hardware design: > +++++ > * FTM source clock is selectable > * Source clock can be the system clock, the fixed frequency clock, or an external > clock > * Fixed frequency clock is an additional clock input to allow the selection of an on > chip clock source other than the system clock > * Selecting external clock connects FTM clock to a chip level input pin therefore > allowing to synchronize the FTM counter with an off chip clock source > ----- > From the above description we can see that the external clock source can allow to synchronize the > FTM counter with an off chip clock source. > > As the chip spec permits the counter clock source be selectable, so the different board maybe has different > implementation, if the driver do not support, this will be a bug. The binding specs the HW so what a driver does or doesn't support isn't relevant. Since I assume only one of these clocks makes sense for a given system I don't see a reason the binding should not just state that a given dts will have the one the system specified rather than all 3. >>> +- pinctrl-names: must contain a "default" entry. >>> +- pinctrl-NNN: One property must exist for each entry in pinctrl-names. >>> + See ../pinctrl/pinctrl-bindings.txt for details of the property >> values. >> >> let's drop the .. when making directory references. >> > > Is absolute path " Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt " or just "pinctrl/pinctrl-bindings.txt " ? The later. - k -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
