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

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Date:	Sun, 30 Nov 2008 07:33:50 +0800
From:	"Jaya Kumar" <jayakumar.lkml@...il.com>
To:	"David Brownell" <david-b@...bell.net>
Cc:	"Sam Ravnborg" <sam@...nborg.org>,
	"Eric Miao" <eric.y.miao@...il.com>,
	"Eric Miao" <eric.miao@...vell.com>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Philipp Zabel" <philipp.zabel@...il.com>,
	"Russell King" <rmk@....linux.org.uk>,
	"Ben Gardner" <bgardner@...tec.com>, "Greg KH" <greg@...ah.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org
Subject: Re: [RFC 2.6.27 1/1] gpiolib: add support for batch set of pins

Jean emailed me saying he didn't want to be CCed.

On Sun, Nov 30, 2008 at 6:48 AM, David Brownell <david-b@...bell.net> wrote:
> On Thursday 27 November 2008, Sam Ravnborg wrote:
>> > > So my "is it generic enough" question is more at the level of "Are
>> > > there enough Linux systems that need this sort of thing to justify
>> > > generic support?".  I happen not to have come across the need for
>> > > such ganged access from Linux (yet).  Whereas I've yet to use non-x86
>> > > Linux systems that don't need to manipulate individual GPIO pins...
>> >
>> > I have come across the following scenarios where a bus set of gpio is useful:
>> > - Broadsheet E-Ink controller (uses 16-bit data bus over GPIO)
>> >   framebuffer device (this patch is for this)
>> > - Apollo/Hecuba E-Ink controller (uses 8-bit data bus over GPIO)
>> >   framebuffer device
>> > - 8-bit parallel IO matrix LCD controllers, such as the Samsung KS108,
>> >   also Hitachi, etc
>
> All of those can also be handled with traditional parallel data
> busses too, of course.  Are you saying you've seen these used
> with Linux systems?  Enough to justify generic support?

Assuming I've understood you correctly about generic support, yes. I
used the 3 above with Linux arm systems that were interfaced to them
via gpio. The matrix displays had just 128x64 so the 8x gpio_set_value
penalty wasn't a biggie. The E-Ink displays range from 800x600 to
1200x826 so the 16x gpio_set_value became a bottleneck. In terms of
generic support, the Broadsheet display controller is also used on
i.MX31 and SC2410/2440 boards so those platform drivers (assuming
those good folks submit them, (i've only written and submitted
am300epd.c)) should also benefit.

Thanks,
jaya
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