Date: Fri, 07 Nov 2014 09:57:23 -0700 From: Ian Lepore <ian@FreeBSD.org> To: Adrian Chadd <adrian@freebsd.org> Cc: "freebsd-arm@freebsd.org" <arm@freebsd.org>, "freebsd-embedded@freebsd.org" <embedded@freebsd.org>, Rui Paulo <rpaulo@me.com> Subject: Re: libgpio Message-ID: <1415379443.1200.215.camel@revolution.hippie.lan> In-Reply-To: <CAJ-VmokCe3smZPQmTtz2QXf5Wou-gUV%2BWO3RX3=1o-=MFYc2BA@mail.gmail.com> References: <B3B50210-8AE9-411A-84B1-AE6C10494149@me.com> <58908C87-6046-4873-87B1-74995EFA72D1@bsdimp.com> <CAJ-VmokCe3smZPQmTtz2QXf5Wou-gUV%2BWO3RX3=1o-=MFYc2BA@mail.gmail.com>
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On Fri, 2014-11-07 at 08:33 -0800, Adrian Chadd wrote: > Hi, >=20 > Yes, it'd be nice to (later) add an API call that takes multiple pin > updates (and reads multiple pin updates.) That way higher speed, time > critical stuff can be done for drivers that grow this feature and can > do batched/timestamped GPIO events. >=20 >=20 >=20 > -adrian >=20 mixed bottom/top posting. grrrr. comments below, where they belong. >=20 > On 7 November 2014 07:44, Warner Losh <imp@bsdimp.com> wrote: > > > > On Nov 6, 2014, at 11:41 PM, Rui Paulo <rpaulo@me.com> wrote: > > > >> Hi, > >> > >> Some time ago, I wrote a gpio library as a way to interact with the = kernel gpio driver in a more sensible way (hiding the details of opening = a /dev file, handling all the ioctls, etc.). > >> > >> Here's the project code: > >> > >> https://bitbucket.org/rpaulo/libgpio/src > >> > >> Here's the header file: > >> > >> https://bitbucket.org/rpaulo/libgpio/src/1dfe793d0b0cd6caff2e1= 96cf667a5c06bbade8d/libgpio.h?at=3Ddefault > >> > >> It looks like some people started using the library and I was wonder= ing if it would be a good candidate for the base system. I would rewrite= gpioctl to use it and I'm open to changing the library API. > >> > >> Any comments? > > > > I generally like it. Here=92s some suggestions, though many may be ha= rd given that our gpio interface is a bit weak. > > > > First, there=92s no way to set multiple pins at the same time. That=92= s likely a reflection of our GPIO system, I know, but it is a deficiency.= Fortunately, most devices can tolerate multiple pins changing at differe= nt times before a =91clock=92 or =91enable=92 pin forces them to latch th= eir state. > > > > What the heck is g_caps? There=92s nothing at all to describe it. Not= even an indirection to look at sys/gpio.h > > > > For systems that have multiple GPIO devices (some have a few hundred = I/O lines that can be addressed), how > > do you handle that? Do you just kinda have to know these details? > > > > There=92s no facilities for interrupts (usually you=92d like to say =93= wait for this line to change and let me know=94). I know that the Atmel g= pio stuff did this, but I don=92t think that made it into the generalizat= ion that was later done. > > > > I=92m not sure that I like the gpio_pin_* helper functions causing th= e thing to change, rather than operating on a gpio_config_t. But since yo= u don=92t normally change a bunch at a time, that=92s not so bad. > > > > Finally a question: What does Linux do here? Is there a standard inte= rface that we could use to leverage off applications written for Linux? P= erhaps beyond the scope of what you=92re trying to do, but any discussion= about pushing things into the base should ask the question =93Is this th= e right, most useful interface?=94 > > > > Warner Multiple-pin read/write is really required for anything other than trivial "turn on this led" type stuff. A restriction that all the pins have to be on the same /dev/gpiocN device is fine. Routines to do simple bit-banging (so that multiple bits can be banged out with a single call) are also good to have. It's good for a driver to support an api for that at the lowest level to get reasonable speed for things like programming an fpga. (The at91 gpio drivers do this now.) -- Ian
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