linux-kernel - Re: [Linux-fbdev-devel] [RFC 2.6.27 1/1] gpiolib: add support for batch set of pins

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Date:	Wed, 26 Nov 2008 05:25:57 -0500
From:	"Jaya Kumar" <jayakumar.lkml@...il.com>
To:	"Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:	"Paulius Zaleckas" <paulius.zaleckas@...tonika.lt>,
	"David Brownell" <dbrownell@...rs.sourceforge.net>,
	linux-fbdev-devel@...ts.sourceforge.net,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Greg KH" <greg@...ah.com>, linux-kernel@...r.kernel.org,
	"David Brownell" <david-b@...bell.net>,
	"Ben Gardner" <bgardner@...tec.com>,
	"Eric Miao" <eric.miao@...vell.com>,
	"Philipp Zabel" <philipp.zabel@...il.com>,
	"Sam Ravnborg" <sam@...nborg.org>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	"Russell King" <rmk@....linux.org.uk>
Subject: Re: [Linux-fbdev-devel] [RFC 2.6.27 1/1] gpiolib: add support for batch set of pins

On Wed, Nov 26, 2008 at 5:08 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Wed, 26 Nov 2008, Jaya Kumar wrote:
>> On Wed, Nov 26, 2008 at 4:09 AM, Paulius Zaleckas
>> <paulius.zaleckas@...tonika.lt> wrote:
>> > Jaya Kumar wrote:
>> >>   * @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
>> >
>>
>> Okay, can do but it is unusual no? since set uses int value, i figured
>> set_bus should be similar right?
>
> ->set() sets one pin, right? So it's either 0 or 1.
>
> ->set_bus() sets multiple pins. With `int', it will fail for bit 31, as that's
> the sign bit.

I'm not sure I understood this. I imagine the usage will be like

int values = 0x8000_0000;
set_bus(..., start_pin, values);

write_32(register, values); // will still work to set bit 31
(values >> 31) == 1;

>
> Perhaps you even want u32, to make it clear what's the maximum number of pins
> you can set in one shot?

Yes, I agree, I will change to use u32 as it is then explicit.

Thanks,
jaya
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