linux-kernel - Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on Intel Baytrail

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Message-ID: <20141013191405.GB29810@saruman>
Date:	Mon, 13 Oct 2014 14:14:05 -0500
From:	Felipe Balbi <balbi@...com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
CC:	<linus.walleij@...aro.org>, <linux-kernel@...r.kernel.org>,
	<linux-gpio@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: baytrail: show output gpio state correctly on
 Intel Baytrail

On Mon, Oct 13, 2014 at 11:23:59AM -0700, David Cohen wrote:
> Even if a gpio pin is set to output, we still need to set INPUT_EN bit

here you say you're setting that bit.

> to be able to read its value. Without this change, we'll always read low
> level state.
> 
> Cc: <stable@...r.kernel.org> # v3.14+
> Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> ---
> 
> Hi,
> 
> I'm resending same v1 patch but now copying linux stable and linux gpio.
> This patch is meant for all linux stable trees >= v3.14.
> 
> Br, David
> ---
> 
>  drivers/pinctrl/pinctrl-baytrail.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pinctrl/pinctrl-baytrail.c b/drivers/pinctrl/pinctrl-baytrail.c
> index e12e5b07f6d7..c23d8ded936d 100644
> --- a/drivers/pinctrl/pinctrl-baytrail.c
> +++ b/drivers/pinctrl/pinctrl-baytrail.c
> @@ -318,7 +318,7 @@ static int byt_gpio_direction_output(struct gpio_chip *chip,
>  		"Potential Error: Setting GPIO with direct_irq_en to output");
>  
>  	reg_val = readl(reg) | BYT_DIR_MASK;
> -	reg_val &= ~BYT_OUTPUT_EN;
> +	reg_val &= ~(BYT_OUTPUT_EN | BYT_INPUT_EN);

but code is clearing it. Also, you're not patching byt_gpio_get(), so
you can't be 'reading its value' either. Quite frankly, this looks very
fishy to me. Comments on BYT_OUTPUT_EN and BYT_INPUT_EN states that
those bits are active low, meaning that clearing them enables that
particular feature.

How can you enable a pin to be both OUTPUT and INPUT ? Look like what
you really want is:

diff --git a/drivers/pinctrl/pinctrl-baytrail.c b/drivers/pinctrl/pinctrl-baytrail.c
index e12e5b0..69f882d 100644
--- a/drivers/pinctrl/pinctrl-baytrail.c
+++ b/drivers/pinctrl/pinctrl-baytrail.c
@@ -290,6 +290,7 @@ static int byt_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
 
 	value = readl(reg) | BYT_DIR_MASK;
 	value &= ~BYT_INPUT_EN;		/* active low */
+	value |= BYT_OUTPUT_EN;		/* disable output */
 	writel(value, reg);
 
 	spin_unlock_irqrestore(&vg->lock, flags);
@@ -319,6 +320,7 @@ static int byt_gpio_direction_output(struct gpio_chip *chip,
 
 	reg_val = readl(reg) | BYT_DIR_MASK;
 	reg_val &= ~BYT_OUTPUT_EN;
+	value |= BYT_INPUT_EN;		/* disable input */
 
 	if (value)
 		writel(reg_val | BYT_LEVEL, reg);

completely untested however. Care to further explain why clearing both
bits - thus enabling both INPUT and OUTPUT - is correct ?

-- 
balbi

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