linux-kernel - Re: [PATCH 3/7] gpio: omap: fix omap2_set_gpio

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Date:	Wed, 26 Aug 2015 09:49:34 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	Alexandre Courbot <gnurou@...il.com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Tony Lindgren <tony@...mide.com>,
	Javier Martinez Canillas <javier@...hile0.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] gpio: omap: fix omap2_set_gpio_debounce

On Tue, Aug 18, 2015 at 1:10 PM, Grygorii Strashko
<grygorii.strashko@...com> wrote:

> According to TRMs:
>
> Required input line stable =
>   (the value of the GPIO_DEBOUNCINGTIME[7:0].DEBOUNCETIME + 1) × 31,
> where the value of the GPIO_DEBOUNCINGTIME[7:0].DEBOUNCETIME bit field
> is from 0 to 255.
>
> But now omap2_set_gpio_debounce() will calculate debounce time and
> behave incorrectly in the following cases:
> 1) requested debounce time is !0 and <32
>    calculated DEBOUNCETIME = 0x1 == 62 us;
>    expected value of DEBOUNCETIME = 0x0 == 31us
> 2) requested debounce time is 0
>    calculated DEBOUNCETIME = 0x1 == 62 us;
>    expected: disable debounce and DEBOUNCETIME = 0x0
> 3) requested debounce time is >32 and <63
>    calculated DEBOUNCETIME = 0x0 and debounce will be disabled;
>    expected: enable debounce and DEBOUNCETIME = 0x1 == 62 us
>
> Hence, rework omap2_set_gpio_debounce() to fix above cases:
> 1) introduce local variable "enable" and use it to identify
> when debounce need to be enabled or disabled. Disable debounce
> if requested debounce time is 0.
> 2) use below formula for debounce time calculation:
>    debounce = (DIV_ROUND_UP(debounce, 31) - 1) & 0xFF;
>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>

Very hightech. Patch applied.

Yours,
Linus Walleij
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