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Date: Mon, 28 Apr 2008 20:44:00 -0700 From: David Brownell <david-b@...bell.net> To: Ben Nizette <bn@...sdigital.com> Cc: lkml <linux-kernel@...r.kernel.org>, Trent Piepho <tpiepho@...escale.com>, hartleys <hartleys@...ionengravers.com>, Mike Frysinger <vapier.adi@...il.com>, Bryan Wu <cooloney@...nel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [patch/rfc 2.6.25-git] gpio: sysfs interface On Monday 28 April 2008, Ben Nizette wrote: > > Ah well we're backwards there, though now I think of it I can't think of > a great many valid use-cases on my side. Just for funzies I'll post on > the avrfreaks AVR32 support forum and see how many I can actually dig > up. Use cases would always help clarify things. I've seen just enough to make me understand this is a useful feature, and for more reasons than just "feature equality" letting us obsolete three drivers/i2c/chips/*.c drivers and help vanish half a dozen (at least!) out-of-tree drivers doing that. The Gumstix user forums and wiki may help too. ISTR they have such a GPIO widget (maybe that's the one I saw which supports polling?) and have shipped it for ages ... so they will surely have some (PXA-specific) examples lurking. > > Trent pointed out that dynamic range assignment can make trouble, > > so I can see some help might be needed here. Were you suggesting > > something like a /sys/class/gpio/chips file with contents like > > > > 0-15 gpio > > 16-31 gpio > > 32-47 gpio > > 48-63 gpio > > 192-207 mpuio > > 208-213 tps65010 > > > > (Matching a stock OMAP 5912 OSK board, for what it's worth.) > > Yeah that's the kind of a thing. Would be well worth having that info > especially for dynamically allocated chip bases. I'd have no problem with that. Some people surely would though; it has more than one value in that file! OMG, it's readable! We can't have any of that!! The Earth will turn in its grave! And Slashdot will be decorated in Pink! Teh End Daze arrive! :) > > > > The D-space footprint is negligible, except for the sysfs resources > > > > associated with each exported GPIO. The additional I-space footprint > > > > is about half of the current size of gpiolib. No /dev node creation > > > > involved, and no "udev" support is needed. > > > > > > Which is good for simplicity but makes async notification kinda tricky. > > > > Sysfs attributes are supposed to be pollable. I've not done it, > > but fs/sysfs/file.c::sysfs_notify() looks relevant ... > > Right, that'll work. OK. In that case, I think I should plan to rename the "direction" attribute as "configuration" or something a bit broader ... so that writing "irq" (or maybe "rising", "falling", "bothedges", "poll") would eventually configure it as an input with an IRQ handler. Whenever someone contributes such an async notification scheme, that is. ;) - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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