Date: Sun, 19 Aug 2012 20:14:55 -0600 From: Warner Losh <imp@bsdimp.com> To: Tim Kientzle <tim@kientzle.com> Cc: gonzo@freebsd.org, freebsd-arm@freebsd.org Subject: Re: gpiobus_hinted_child >32 pins support, pin_getname method, and gpio-sysctl bridge patch Message-ID: <284D7D21-D87B-4112-BBDB-17CA0F9A6FDD@bsdimp.com> In-Reply-To: <1501020F-38C8-44E9-82B3-64DF1090A983@kientzle.com> References: <20120819.171723.523519054460575158.hrs@allbsd.org> <8CDAB51C-14A0-42F0-8E16-43A3EABA2703@bsdimp.com> <E7C5ED5C-7120-4B69-9146-D9CC7A8E14C2@kientzle.com> <7E6C76BE-1D3F-40E4-BFE3-DC88715C234C@bsdimp.com> <12A967D8-BC49-49AF-BBD9-40E259932617@kientzle.com> <974EEF9B-08C2-4876-9223-48DD4ABDFC99@bsdimp.com> <1501020F-38C8-44E9-82B3-64DF1090A983@kientzle.com>
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On Aug 19, 2012, at 6:45 PM, Tim Kientzle wrote: >=20 > On Aug 19, 2012, at 4:42 PM, Warner Losh wrote: >=20 >>=20 >> On Aug 19, 2012, at 5:04 PM, Tim Kientzle wrote: >>=20 >>> On Aug 19, 2012, at 10:02 AM, Warner Losh wrote: >>>>=20 >>>> On Aug 19, 2012, at 10:03 AM, Tim Kientzle wrote: >>>>=20 >>>>> On Aug 19, 2012, at 8:38 AM, Warner Losh wrote: >>>>>=20 >>>>>>=20 >>>>>> In general, I like this code in the context of the current GPIO = framework. I've been growing dissatisfied with the current GPIO = framework, however, and some of my comments reflect that more than any = comments about this specific code. >>>>>=20 >>>>> I noticed that Linux on BeagleBone does not >>>>> simply number all pins as we do. Pins are identified by >>>>> two numbers: a unit number and a pin number. >>>>=20 >>>> Is this in the code, or just in the FTD? On Atmel, there's a = single number from 0 to max-1 with all negative numbers being invalid. = But Atmel doesn't have proper FTD support in Linux just yet (3.5 has a = good start, and 3.6 will add the missing pinmux/pinctl stuff). >>>=20 >>> I'm not exactly sure what you mean. The Linux DTS file: >>>=20 >>> = http://git.kernel.org/?p=3Dlinux/kernel/git/torvalds/linux.git;a=3Dblob;f=3D= arch/arm/boot/dts/am335x-bone.dts >>>=20 >>> inherits most of the real functionality from >>>=20 >>> = http://git.kernel.org/?p=3Dlinux/kernel/git/torvalds/linux.git;a=3Dblob;f=3D= arch/arm/boot/dts/am33xx.dtsi >>>=20 >>> There are certainly separate entries there for each GPIO module. I = presume (but haven't verified) that the unit number maps directly to a = "gpio#" device name. >>=20 >> There's similar things in the Atmel DTS files, but under the covers = the gpio pins map into a uniform space number 0 to 32*N-1, where N is = the number of GPIO units. >=20 > The "under the covers" part is exactly what bothers me > about this. This makes a number of interfaces a simple int, rather than having some = kind of struct. > I've been reading documentation that says things like > "LED#0 on the board is connected to GPIO#1 pin 13". I'd > like to be able to take that to the command line and type in: > $ gpio 1 13 on > or > $ gpio /dev/gpio1 13 on > and see LED#0 turn on. Yet other documentation says "The LED is connected to PC23" which has no = simple mapping to this stuff. Sure that's gpio2, since that's what = would most likely get PIOC from the chip, but it could just as easily be = 3 since C is the 3rd letter of the alphabet. > Since GPIO is used by a lot of folks interfacing new > hardware, this kind of translation between hardware > interface and software API needs to be trivial. Correct. The current mapping we have is insane. We have to have a = base-address of the GPIO hardware, coupled with a mask and pass that = complex thing around, when we could more easily pass around a simple = int. Linux did it this way to make their board files easier to cope = with. I'm not sure how it is exposed outside the kernel, honestly. = Given the trend to FDT, tuples aren't too bad to carry around since you = don't have to contrive them to be in free code as much. > How would the linear addressing approach > handle, for example, hot-plugging of a device that > provided a USB interface to a group of GPIO pins? > (That is, it plugs into the USB port on the board > and provides a GPIO header on the other end. > Not vice versa. ;-) Each platform would have a fixed set of pins, followed by a dynamically = allocated range for the odd-ball situations like this. For most things, gpio does single bit, and for single bit on one of many = GPIOs units, masks are a pain. But until I have gpioNG going, along with the pinctl and pinmux support = with DTS tie ins, I guess I'm just flapping my yapper, eh? Warner
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