Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib

[Ben Nizette]

On 18/04/2011, at 7:37 AM, Linus Walleij wrote:

> From: Linus Walleij <linus.walleij@xxxxxxxxxx>
> 
> This adds two functions for struct gpio_chip chips to provide pin
> bias and drive mode settings for individual pins. Implementers does
> this a bit differently and usually there are a few possible modes you
> can select, I'm providing a few common modes for biasing and driving
> pins.
> 
> Since we have no previous hacked-up arch-specific drivers for this
> we can avoid any __override_functions and we just allow this to be
> properly implemented using gpiolib. Further the function is made
> non-mandatory, if it is not defined for the chip it will be silently
> ignored.

I don't like this much.  Why does the driver ever need to do this?  When should a driver even try this this given you can't guarantee any results and as such it's only ever a hint?  As far as I can see it would be much much better if you just replaced

platform_device_register(...)

with

set_up_pins(...)
platform_device_register(...)

in board code (or add a device tree, erm, leaf or whatever).  Especially things like pin drive strength is meaningless to a driver and would, I imaging, be passed through the plaform data from the board in the common case anyway.

gpiolib handles input and output, high and low because that's all that could reasonably be expected to a) always work and b) be changed at run time in the driver.

So in short - what's the use case?  Which driver requires this?

Thanks!
	--Ben.

p.s. forgive the (lack of) word wrapping, travelling with a dumb-arse mail client atm :)

> 
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> drivers/gpio/gpiolib.c     |   43 ++++++++++++++++++++++++++++++++++++++
> include/asm-generic/gpio.h |   12 ++++++++++
> include/linux/gpio.h       |   49 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 104 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 36a2974..f79f4a3 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1573,6 +1573,49 @@ void __gpio_set_value(unsigned gpio, int value)
> EXPORT_SYMBOL_GPL(__gpio_set_value);
> 
> /**
> + * gpio_set_bias() - set a gpio's bias
> + * @gpio: gpio whose bias will be set
> + * @bias: bias mode to set
> + * Context: process
> + *
> + * This is used to directly or indirectly to implement gpio_set_bias().
> + * It invokes the associated gpio_chip.set_bias() method. Usually this
> + * applies to input pins.
> + */
> +void gpio_set_bias(unsigned gpio, enum gpio_bias bias)
> +{
> +	struct gpio_chip	*chip;
> +
> +	chip = gpio_to_chip(gpio);
> +	/* Implementing this is not mandatory */
> +	if (chip->set_bias)
> +		chip->set_bias(chip, gpio - chip->base, bias);
> +}
> +EXPORT_SYMBOL_GPL(gpio_set_bias);
> +
> +/**
> + * gpio_set_drive() - set a gpio's drive mode
> + * @gpio: gpio whose drive mode will be set
> + * @drive: drive mode to set
> + * Context: process
> + *
> + * This is used to directly or indirectly to implement gpio_set_drive().
> + * It invokes the associated gpio_chip.set_drive() method. Call this
> + * before the __gpio_set_output() function to enable special drive modes.
> + */
> +void gpio_set_drive(unsigned gpio, enum gpio_drive drive)
> +{
> +	struct gpio_chip	*chip;
> +
> +	chip = gpio_to_chip(gpio);
> +	/* Implementing this is not mandatory */
> +	if (chip->set_drive)
> +		chip->set_drive(chip, gpio - chip->base, drive);
> +}
> +EXPORT_SYMBOL_GPL(gpio_set_drive);
> +
> +
> +/**
>  * __gpio_cansleep() - report whether gpio value access will sleep
>  * @gpio: gpio in question
>  * Context: any
> diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
> index ff5c660..b4971b1 100644
> --- a/include/asm-generic/gpio.h
> +++ b/include/asm-generic/gpio.h
> @@ -59,6 +59,8 @@ struct device_node;
>  *	returns either the value actually sensed, or zero
>  * @direction_output: configures signal "offset" as output, or returns error
>  * @set: assigns output value for signal "offset"
> + * @set_bias: set a certain bias for the GPIO
> + * @set_drive: set a certain drive mode for the GPIO
>  * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;
>  *	implementation may not sleep
>  * @dbg_show: optional routine to show contents in debugfs; default code
> @@ -109,6 +111,14 @@ struct gpio_chip {
> 	void			(*set)(struct gpio_chip *chip,
> 						unsigned offset, int value);
> 
> +	void			(*set_bias)(struct gpio_chip *chip,
> +						unsigned offset,
> +						enum gpio_bias bias);
> +
> +	void			(*set_drive)(struct gpio_chip *chip,
> +						unsigned offset,
> +						enum gpio_drive drive);
> +
> 	int			(*to_irq)(struct gpio_chip *chip,
> 						unsigned offset);
> 
> @@ -158,6 +168,8 @@ extern int gpio_set_debounce(unsigned gpio, unsigned debounce);
> extern int gpio_get_value_cansleep(unsigned gpio);
> extern void gpio_set_value_cansleep(unsigned gpio, int value);
> 
> +extern void gpio_set_bias(unsigned gpio, enum gpio_bias bias);
> +extern void gpio_set_drive(unsigned gpio, enum gpio_drive drive);
> 
> /* A platform's <asm/gpio.h> code may want to inline the I/O calls when
>  * the GPIO is constant and refers to some always-present controller,
> diff --git a/include/linux/gpio.h b/include/linux/gpio.h
> index 32720ba..6b48c15 100644
> --- a/include/linux/gpio.h
> +++ b/include/linux/gpio.h
> @@ -3,6 +3,43 @@
> 
> /* see Documentation/gpio.txt */
> 
> +/**
> + * enum gpio_bias - bias modes for GPIOs
> + * @GPIO_BIAS_FLOAT: no specific bias, the GPIO will float or state is no
> + * 	controlled by software
> + * @GPIO_BIAS_PULL_UP: the GPIO will be pulled up (usually with high impedance
> + * 	to VDD)
> + * @GPIO_BIAS_PULL_DOWN: the GPIO will be pulled down (usually with high
> + * 	impedance to GROUND)
> + * @GPIO_BIAS_HIGH: the GPIO will be wired high, connected to VDD
> + * @GPIO_BIAS_GROUND: the GPIO will be grounded, connected to GROUND
> + */
> +enum gpio_bias {
> +	GPIO_BIAS_FLOAT,
> +	GPIO_BIAS_PULL_UP,
> +	GPIO_BIAS_PULL_DOWN,
> +	GPIO_BIAS_HIGH,
> +	GPIO_BIAS_GROUND,
> +};
> +
> +/**
> + * enum gpio_drive - drive modes for GPIOs (output)
> + * @GPIO_DRIVE_PUSH_PULL: the GPIO will be driven actively high and low, this
> + *	is the most typical case and is typically achieved with two active
> + *	transistors on the output
> + * @GPIO_DRIVE_OPEN_DRAIN: the GPIO will be driven with open drain (open
> + *	collector) which means it is usually wired with other output ports
> + *	which are then pulled up with an external resistor
> + * @GPIO_DRIVE_OPEN_SOURCE: the GPIO will be driven with open drain
> + *	(open emitter) which is the same as open drain mutatis mutandis but
> + *	pulled to ground
> + */
> +enum gpio_drive {
> +	GPIO_DRIVE_PUSH_PULL,
> +	GPIO_DRIVE_OPEN_DRAIN,
> +	GPIO_DRIVE_OPEN_SOURCE,
> +};
> +
> #ifdef CONFIG_GENERIC_GPIO
> #include <asm/gpio.h>
> 
> @@ -90,6 +127,18 @@ static inline void gpio_set_value(unsigned gpio, int value)
> 	WARN_ON(1);
> }
> 
> +static inline void gpio_set_bias(unsigned gpio, enum gpio_bias bias)
> +{
> +	/* GPIO can never have been requested */
> +	WARN_ON(1);
> +}
> +
> +static inline void gpio_set_drive(unsigned gpio, enum gpio_drive drive)
> +{
> +	/* GPIO can never have been requested */
> +	WARN_ON(1);
> +}
> +
> static inline int gpio_cansleep(unsigned gpio)
> {
> 	/* GPIO can never have been requested or set as {in,out}put */
> -- 
> 1.7.3.2
> 
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