Date: Fri, 6 Sep 2013 17:13:20 -0600 From: John Hein <jhein@symmetricom.com> To: Ian Lepore <ian@FreeBSD.org> Cc: freebsd-embedded <freebsd-embedded@FreeBSD.org> Subject: Re: GPIO hint meanings Message-ID: <21034.24976.184098.797870@gromit.timing.com> In-Reply-To: <1378506465.1111.489.camel@revolution.hippie.lan> References: <1378488150.1637.5.camel@localhost> <CAB=2f8yEx4UPc1QeHP%2BbJCDadDRvBJyvTkPjztVv4VG5uoULQw@mail.gmail.com> <097A9AFF-D291-4D9F-92CC-12E5E453F7C7@bsdimp.com> <1378504840.1111.480.camel@revolution.hippie.lan> <A42A2E89-E650-4FF4-ACE3-556A8FF02E22@bsdimp.com> <1378506465.1111.489.camel@revolution.hippie.lan>
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Ian Lepore wrote at 16:27 -0600 on Sep 6, 2013: > On Fri, 2013-09-06 at 16:13 -0600, Warner Losh wrote: > > On Sep 6, 2013, at 4:00 PM, Ian Lepore wrote: > > > On Fri, 2013-09-06 at 13:42 -0600, Warner Losh wrote: [snip] > > >> We really need a pinmux/pinctl type interface for this which is standard across drivers/platforms. > > > > > > The more ARM SoCs I look at, the less I think we could design a single > > > pinmux api that works for all of them. The number of things that can be > > > controlled varies from almost-nothing to chips that let you select from > > > one of a dozen different resistor strengths for pullup or pulldown per > > > pin. And that's not to mention really crazy things like daisy-chaining > > > pins so the signal also goes to another pin which can be forced as an > > > input even though it's normally a device output. > > > > Linux is able to have one, although I'm not sure how they handle the daisy-chain... that's a new one on me... > > Maybe they just don't, since it's a weird enough thing that probably > nothing uses it. I only discovered it because the datasheet said it was > a potential workaround for an erratum that had to do with a device not > handling a pin properly. They love their special filesystems, they do. I suspect the first hacker to add support for fancy new GPIO feature for whatever gets to pick the "filename" in the /sys/clas/gpio/gpioX tree or special value to echo > to it. https://www.kernel.org/doc/Documentation/gpio.txt > The semi-related thing I've been pondering lately is clock and power > management. I don't even care about dynamic stuff, just a simple common > way for a driver to figure out what clock(s) and/or power need to be on > for it to run, and a common api for turning them on would be nice. > (Whether clocks and power should be two separate APIs or not is a basic > question.)
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