Hi Linus,
On 2018/4/12 19:47, Linus Walleij wrote:
On Thu, Apr 12, 2018 at 10:14 AM, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
On 2018/4/12 15:58, Ulf Hansson wrote:
On 12 April 2018 at 09:34, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
However if I understand correctly, you are suggesting to use a 200 ms
default debounce value - and in case that is succeeded to be set for
the GPIO, then we don't need the delay when scheduling the detect
work. No?
On top of that, you want the debounce value to come from DT?
In case the debounce is passed on from the caller, it means the caller
drivers want it. So we firstly try it by using gpio debounce, but anyway we
could fall back to use software debounce method, namely
mmc_detect_change(host, msecs_to_jiffies(ctx->cd_delay_ms));
ctx->cd_delay_ms = max_t(unsigned int, debounce, 200) could make sure
we at least have a basic 200ms delay which keeps consistent with current
code. But a longer delay is better if the caller ask it via debounce
argument.
The debounce time is dependent on use case so it makes sense
for this to come from the configuration for a certain system.
200ms makes a lot of sense though.
But there is a real problem with the bigger picture here.
Please consult:
drivers/input/keyboard/gpio_keys.c
As you can see, GPIO keys implements a timer-based
software delay. The good thing is that this is thoroughly tested
code so if you do this, look at how the input subsystem is
doing it. A key isn't very different from a MMC/SD card slot.
But the hippo in the living room is of course that this will
lead to code duplication. Reinventing the wheel.
What I would like to happen, is for software debouncing
to be moved into gpiolib and used as a fallback in the cases
where the hardware does not support debounce.
This way gpiod_set_debounce() will never fail with -ENOTSUPP
and we can remove the code from in the input subsystem
and reuse it freely for MMC/SD card detection. Probably also
in drivers/extcon etc.
To me this makes most sense.
I understand it might be a bit much to ask and I think I tried
My current plan is still to slightly improve this in MMC/SD slot-gpio
code but not touch timer-based software debouce as you may understand
that I need backport it for my employer in short-term, expecially they
argue upstream first. :)
But I'm interested in timer-based software debouce support in GPIO,
and will have a look it later. Btw, have you post patch(es) for thatin
the past? It should be helpful for me to investigate it if you could
share a link.
to factor this over from input to GPIO at one point but
failed. Would you like to give it a try, or do you want me to
take a stab at it? (It might take some time...)
Yours,
Linus Walleij
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