[PATCH] gpio: max732x: fix input configuration for open-drain pins

[PATCH] gpio: max732x: fix input configuration for open-drain pins

[Marc Zyngier]

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Eric,

The attached patch tries to fix a bug I noticed while hacking on the
max732x driver for interrupt support.
According to the datasheets, open-drain pins have to be configured as
output-high (which in that case is actually high impedance) to be used as
input.

Note that this patch has only been compile tested, as I still have to
solder the actual chip to one of my boards...

Thanks,

        M.
-- 
Who you jivin' with that Cosmik Debris?

[-- Attachment #2: 0002-gpio-max732x-fix-input-configuration-for-open-drain-.patch --]
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From 059eb9b61b276a681d634781abaa1159dfb547bc Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@misterjones.org>
Date: Mon, 15 Mar 2010 22:14:51 +0000
Subject: [PATCH] gpio: max732x: fix input configuration for open-drain pins

max732x datasheets indicate that open-drain pins must be
configured as output-high to be used as input...

Signed-off-by: Marc Zyngier <maz@misterjones.org>
---
 drivers/gpio/max732x.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/drivers/gpio/max732x.c b/drivers/gpio/max732x.c
index f786824..3618feb 100644
--- a/drivers/gpio/max732x.c
+++ b/drivers/gpio/max732x.c
@@ -179,15 +179,25 @@ static int max732x_gpio_direction_input(struct gpio_chip *gc, unsigned off)
 {
 	struct max732x_chip *chip;
 	unsigned int mask = 1u << off;
+	unsigned int is_input;
 
 	chip = container_of(gc, struct max732x_chip, gpio_chip);
 
-	if ((mask & chip->dir_input) == 0) {
+	is_input = mask & chip->dir_input;
+
+	if (!is_input) {
 		dev_dbg(&chip->client->dev, "%s port %d is output only\n",
 			chip->client->name, off);
 		return -EACCES;
 	}
 
+	/*
+	 * Open-drain pins must be set to high impedance (which is
+	 * equivalent to output-high) to be turned into an input.
+	 */
+	if ((is_input & chip->dir_output))
+		max732x_gpio_set_value(gc, off, 1);
+
 	return 0;
 }
 
-- 
1.7.0.2

Re: [PATCH] gpio: max732x: fix input configuration for open-drain pins

[Eric Miao]

On Tue, Mar 16, 2010 at 5:19 PM, Marc Zyngier <maz@misterjones.org> wrote:
> Eric,
>
> The attached patch tries to fix a bug I noticed while hacking on the
> max732x driver for interrupt support.
> According to the datasheets, open-drain pins have to be configured as
> output-high (which in that case is actually high impedance) to be used as
> input.
>
> Note that this patch has only been compile tested, as I still have to
> solder the actual chip to one of my boards...
>

Ack.

(PS: Sorry for late reply, overlooked.)

Re: [PATCH] gpio: max732x: fix input configuration for open-drain pins

[Andrew Morton]

> On Tue, 16 Mar 2010 10:19:00 +0100

I bet you thought I'd forgotten.

Marc Zyngier <maz@misterjones.org> wrote:

> max732x datasheets indicate that open-drain pins must be
> configured as output-high to be used as input...
> 
> Signed-off-by: Marc Zyngier <maz@misterjones.org>
> ---
>  drivers/gpio/max732x.c |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/gpio/max732x.c b/drivers/gpio/max732x.c
> index f786824..3618feb 100644
> --- a/drivers/gpio/max732x.c
> +++ b/drivers/gpio/max732x.c
> @@ -179,15 +179,25 @@ static int max732x_gpio_direction_input(struct gpio_chip *gc, unsigned off)
>  {
>  	struct max732x_chip *chip;
>  	unsigned int mask = 1u << off;
> +	unsigned int is_input;
>  
>  	chip = container_of(gc, struct max732x_chip, gpio_chip);
>  
> -	if ((mask & chip->dir_input) == 0) {
> +	is_input = mask & chip->dir_input;
> +
> +	if (!is_input) {
>  		dev_dbg(&chip->client->dev, "%s port %d is output only\n",
>  			chip->client->name, off);
>  		return -EACCES;
>  	}
>  
> +	/*
> +	 * Open-drain pins must be set to high impedance (which is
> +	 * equivalent to output-high) to be turned into an input.
> +	 */
> +	if ((is_input & chip->dir_output))

You really did mean `&' here, but one very much expects a variable
called is_foo to be a boolean, and booleans want `&&'.

Can you think of a more appropriate name for this guy?  input_lines, maybe?

> +		max732x_gpio_set_value(gc, off, 1);
> +
>  	return 0;
>  }

Re: [PATCH] gpio: max732x: fix input configuration for open-drain pins

[Marc Zyngier]

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On Tue, 20 Apr 2010 16:51:48 -0700, Andrew Morton
<akpm@linux-foundation.org> wrote:
>> On Tue, 16 Mar 2010 10:19:00 +0100
> 
> I bet you thought I'd forgotten.

Naaaah... I trust your memory more than mine... ;-)

> You really did mean `&' here, but one very much expects a variable
> called is_foo to be a boolean, and booleans want `&&'.

Actually, the attached patch is a much simpler solution to this particular
one. We already checked that the pin is input-capable. Use the same mask to
check that the pin is also output-capable, and thus open-drain. No need for
an additional variable.

Thanks,

        M.
-- 
Who you jivin' with that Cosmik Debris?

[-- Attachment #2: 0001-gpio-max732x-fix-input-configuration-for-open-drain-.patch --]
[-- Type: text/plain, Size: 1154 bytes --]

From 3ff7ff7f13145a6a46ffa2e0cc350bee1f120577 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@misterjones.org>
Date: Fri, 23 Apr 2010 12:25:53 +0100
Subject: [PATCH] gpio: max732x: fix input configuration for open-drain pins

Fix a bug I noticed while hacking on the max732x driver for interrupt
support.  According to the datasheets, open-drain pins have to be
configured as output-high (which in that case is actually high impedance)
to be used as input.

Signed-off-by: Marc Zyngier <maz@misterjones.org>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
---
 drivers/gpio/max732x.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/gpio/max732x.c b/drivers/gpio/max732x.c
index f786824..ad6a80b 100644
--- a/drivers/gpio/max732x.c
+++ b/drivers/gpio/max732x.c
@@ -188,6 +188,13 @@ static int max732x_gpio_direction_input(struct gpio_chip *gc, unsigned off)
 		return -EACCES;
 	}
 
+	/*
+	 * Open-drain pins must be set to high impedance (which is
+	 * equivalent to output-high) to be turned into an input.
+	 */
+	if ((mask & chip->dir_output))
+		max732x_gpio_set_value(gc, off, 1);
+
 	return 0;
 }
 
-- 
1.7.0.4