Messages in this thread | | | Date | Sat, 14 Sep 2013 09:08:24 +0200 | From | boris brezillon <> | Subject | Re: [RFC PATCH alt 4/4] pinctrl: at91: rework debounce configuration |
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Hello Stephen,
Le 14/09/2013 00:40, Stephen Warren a écrit : > On 09/13/2013 01:53 AM, Boris BREZILLON wrote: >> AT91 SoCs do not support per pin debounce time configuration. >> Instead you have to configure a debounce time which will be used for all >> pins of a given bank (PIOA, PIOB, ...). >> diff --git a/Documentation/devicetree/bindings/pinctrl/atmel,at91-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/atmel,at91-pinctrl.txt >> +Optional properties for iomux controller: >> +- atmel,default-debounce-div: array of debounce divisors (one divisor per bank) >> + which describes the debounce timing in use for all pins of a given bank >> + configured with the DEBOUNCE option (see the following description). >> + Debounce timing is obtained with this formula: >> + Tdebounce = 2 * (debouncediv + 1) / Fslowclk >> + with Fslowclk = 32KHz >> + >> Required properties for pin configuration node: >> - atmel,pins: 4 integers array, represents a group of pins mux and config >> setting. The format is atmel,pins = <PIN_BANK PIN_BANK_NUM PERIPH CONFIG>. >> @@ -91,7 +99,6 @@ DEGLITCH (1 << 2): indicate this pin need deglitch. >> PULL_DOWN (1 << 3): indicate this pin need a pull down. >> DIS_SCHMIT (1 << 4): indicate this pin need to disable schmit trigger. >> DEBOUNCE (1 << 16): indicate this pin need debounce. >> -DEBOUNCE_VAL (0x3fff << 17): debounce val. > This change would break the DT ABI since it removes a feature that's > already present.
I missed this point in my cons list. This won't be an issue for in kernel DT definitions (nobody is currently using the DEBOUCE option), but may be for out-of-tree DT definitions.
> I suppose it's still up to the Atmel maintainers to decide whether this > is appropriate, or whether the impact to out-of-tree DT files would be > problematic. > > Assuming the DT ABI can be broken, I think I'd prefer to do so, rather > than take "non-alt" patch 4/4, since a per-pin DEBOUNCE_VAL clearly > doesn't correctly model the HW, assuming the patch description is > correct. I don't think arguments re: the generic pinconf debounce > property hold; if the Linux-specific/internal generic property doesn't > apply, the DT binding should not be bent to adjust to it, but should > rather still represent the HW itself.
What about the last point in my list: "reconfigure debounce after startup" ?
Here is an example that may be problematic:
Let's say you have one device using multiple configuration of pins ("default", "xxx", "yyy"). The "default" config needs a particular debounce time on a given pin and the "xxx" and "yyy" configs need different debounce time on the same pin.
How would you solve this with this patch approach ?
Best Regards,
Boris
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