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

["Jaya Kumar" <jayakumar.lkml@gmail.com>]

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

On Sun, Nov 30, 2008 at 6:48 AM, David Brownell <david-b@pacbell.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