linux-kernel - Re: [PATCH V2 3/3] gpio: tegra: Add support for gpio debounce

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Date:	Tue, 19 Apr 2016 14:36:02 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Laxman Dewangan <ldewangan@...dia.com>, linus.walleij@...aro.org,
	gnurou@...il.com, swarren@...dotorg.org,
	linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] gpio: tegra: Add support for gpio debounce

On Tue, Apr 19, 2016 at 11:43:25AM +0100, Jon Hunter wrote:
> 
> On 19/04/16 10:43, Laxman Dewangan wrote:
> > NVIDIA's Tegra210 support the HW debounce in the GPIO
> > controller for all its GPIO pins.
> > 
> > Add support for setting debounce timing by implementing the
> > set_debounce callback of gpiochip.
> > 
> > Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
> > 
> > ---
> > Changes from V1:
> > - Write debounce count before enable.
> > - Make sure the debounce count do not have any boot residuals.
> > ---
> >  drivers/gpio/gpio-tegra.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> 
> [snip]
> 
> > @@ -327,6 +360,9 @@ static int tegra_gpio_resume(struct device *dev)
> >  			tegra_gpio_writel(bank->oe[p], GPIO_OE(gpio));
> >  			tegra_gpio_writel(bank->int_lvl[p], GPIO_INT_LVL(gpio));
> >  			tegra_gpio_writel(bank->int_enb[p], GPIO_INT_ENB(gpio));
> > +			tegra_gpio_writel(bank->dbc_cnt[p], GPIO_DBC_CNT(gpio));
> > +			tegra_gpio_writel(bank->dbc_enb[p],
> > +					  GPIO_MSK_DBC_EN(gpio));
> 
> If these registers are not valid on Tegra devices prior to Tegra210, I
> don't think we should write to these locations on those devices (even if
> we are writing back the values read).
> 
> > @@ -351,6 +387,10 @@ static int tegra_gpio_suspend(struct device *dev)
> >  			bank->oe[p] = tegra_gpio_readl(GPIO_OE(gpio));
> >  			bank->int_enb[p] = tegra_gpio_readl(GPIO_INT_ENB(gpio));
> >  			bank->int_lvl[p] = tegra_gpio_readl(GPIO_INT_LVL(gpio));
> > +			bank->dbc_enb[p] = tegra_gpio_readl(
> > +							GPIO_MSK_DBC_EN(gpio));
> > +			bank->dbc_enb[p] = (bank->dbc_enb[p] << 8) ||
> > +						bank->dbc_enb[p];
> 
> Same here, not sure we should even bother reading these for Tegra's
> before Tegra210.

Indeed. This patch already introduces the debounce_supported capability
in the SoC data, so access to these registers could be guarded by that.

Thierry

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