Re: [RFC 2.6.27 1/1] gpiolib: add support for batch set of pins

[Paulius Zaleckas]

Jaya Kumar wrote:
> Beloved friends,
> 
> I would like to request your feedback on the following idea. I hope I have
> made sure to CC all the right people and the right lists! If not, PLEASE
> let me know! I couldn't find a MAINTAINERS entry for gpiolib so I just
> used what I saw in the git log and have also added people and lists that
> I think may be interested.
> 
> This is just an RFC. If you all feel it is looking like the right approach
> then I'll clean it up and make it a patch.
> 
> Thanks,
> jaya
> 
> am300epd was doing 800*600*16*gpio_set_value for each framebuffer transfer
> (it uses 16-pins of gpio as its data bus). I found this caused a wee
> performance limitation. This patch adds an API for gpio_set_value_bus
> which allows users to set batches of consecutive gpio together in a single
> call. I have done a test implementation on gumstix (pxa255) with am300epd
> and it provides a nice improvement in performance.
> 
> Signed-off-by: Jaya Kumar <jayakumar.lkml@xxxxxxxxx>
> Cc: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
> Cc: David Brownell <david-b@xxxxxxxxxxx>
> Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
> Cc: Jean Delvare <khali@xxxxxxxxxxxx>
> Cc: Eric Miao <eric.miao@xxxxxxxxxxx>
> Cc: Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>
> Cc: Philipp Zabel <philipp.zabel@xxxxxxxxx>
> Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
> Cc: Ben Gardner <bgardner@xxxxxxxxxx>
> CC: Greg KH <greg@xxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxxxxx
> Cc: linux-fbdev-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> ---
>  arch/arm/mach-pxa/am300epd.c          |    9 ++++++
>  arch/arm/mach-pxa/gpio.c              |   28 +++++++++++++++++++++
>  arch/arm/mach-pxa/include/mach/gpio.h |   24 ++++++++++++++++++
>  drivers/gpio/gpiolib.c                |   44 +++++++++++++++++++++++++++++++++
>  include/asm-generic/gpio.h            |    6 ++++
>  5 files changed, 111 insertions(+), 0 deletions(-)
> 

[...]

> diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
> index 81797ec..9747517 100644
> --- a/include/asm-generic/gpio.h
> +++ b/include/asm-generic/gpio.h
> @@ -44,6 +44,8 @@ struct module;
>   *	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_bus: batch assigns output values for consecutive signals starting at
> + *	"offset" with width in bits "bitwidth"
>   * @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
> @@ -84,6 +86,9 @@ struct gpio_chip {
>  						unsigned offset, int value);
>  	void			(*set)(struct gpio_chip *chip,
>  						unsigned offset, int value);
> +	void			(*set_bus)(struct gpio_chip *chip,
> +						unsigned offset, int values,

I think values should be unsigned

> +						int bitwidth);
>  
>  	int			(*to_irq)(struct gpio_chip *chip,
>  						unsigned offset);
> @@ -124,6 +129,7 @@ extern void gpio_set_value_cansleep(unsigned gpio, int value);
>   */
>  extern int __gpio_get_value(unsigned gpio);
>  extern void __gpio_set_value(unsigned gpio, int value);
> +extern void __gpio_set_value_bus(unsigned gpio, int values, int bitwidth);
>  
>  extern int __gpio_cansleep(unsigned gpio);
>  
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