On Thu, Nov 2, 2017 at 9:32 AM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > On Wed, Nov 1, 2017 at 10:26 PM, Rob Herring <robh@xxxxxxxxxx> wrote: >> On Sat, Oct 28, 2017 at 03:37:17PM +0200, Linus Walleij wrote: >>> Some pin controllers (such as the Gemini) can control the >>> expected clock skew and output delay on certain pins with a >>> sub-nanosecond granularity. This is typically done by shunting >>> in a number of double inverters in front of or behind the pin. >>> Make it possible to configure this with a generic binding. >>> >>> Cc: devicetree@xxxxxxxxxxxxxxx >>> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> >>> --- >>> Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++ >>> drivers/pinctrl/pinconf-generic.c | 2 ++ >>> include/linux/pinctrl/pinconf-generic.h | 5 +++++ >>> 3 files changed, 11 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt >>> index 4483cc31e531..ad9bbbba36e9 100644 >>> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt >>> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt >>> @@ -271,6 +271,10 @@ output-high - set the pin to output mode with high level >>> sleep-hardware-state - indicate this is sleep related state which will be programmed >>> into the registers for the sleep state. >>> slew-rate - set the slew rate >>> +skew-delay - this affects the expected clock skew on input pins >>> + and the delay before latching a value to an output >>> + pin. Typically indicates how many double-inverters are >>> + used to delay the signal. >> >> Units? > > Number of double-inverters I guess, just as it says. > > skew-delay = <1>; // number of inverter pairs > > Like with other bindings of this type they are custom. > > The Gemini datasheet says "every unit represents about 0.2 ns". > > So if you set it to 1, that means (as far as I can guess) this > is shunted in: > > |\ |\ > --+ >o--+ >o--- > |/ |/ > > The signal will take ~0.2 ns to propagate through this. > For 2, there will be four inverters etc. > > It is dependent of production technology, and I do not know > if everyone is using something like double-inverters. > > We could try to define a value in picoseconds instead so I > would need to set this to 200 in that case if you think that is better: > > skew-delay = <200>; // picoseconds > > I think it would be kludgy since with increasing clock speeds > maybe picoseconds would be too big even. Nanoseconds is > apparently already a to coarse unit. Okay, it is fine. Acked-by: Rob Herring <robh@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
