Messages in this thread | | | Date | Mon, 28 Jan 2013 12:39:05 +0100 | Subject | Re: [PATCH 5/6 v14] gpio: Add device tree support to block GPIO API | From | Stijn Devriendt <> |
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On Sun, Jan 27, 2013 at 3:29 PM, Roland Stigge <stigge@antcom.de> wrote: > On 27/01/13 14:07, Stijn Devriendt wrote: >>> +Example: >>> + >>> + blockgpio { >>> + compatible = "linux,gpio-block"; >>> + >>> + block0 { >>> + gpios = <&gpio 3 0 0>, >>> + <&gpio 3 1 0>; >>> + }; >>> + block1 { >>> + gpios = <&gpio 4 1 0>, >>> + <&gpio 4 3 0>, >>> + <&gpio 4 2 0>, >>> + <&gpio 4 4 0>, >>> + <&gpio 4 5 0>, >>> + <&gpio 4 6 0>, >>> + <&gpio 4 7 0>, >>> + <&gpio 4 8 0>, >>> + <&gpio 4 9 0>, >>> + <&gpio 4 10 0>, >>> + <&gpio 4 19 0>; >>> + }; >>> + }; >> >> How do you see bindings for other kinds of drivers? >> >> In my patchset, it's possible for other drivers to use gpio-blocks. >> One example we have is a power sequencer with 2 pins attached >> to GPIO pins. These 2 pins form a 2bit word to select power margining. >> These 2 pins need to be set synchronously (as otherwise when going >> from profile 0 to profile 3 you pass either profile 1 or profile 2 which >> could be bad for hardware) >> >> In the device-tree this is specified as: >> >> powr@0x20 { >> // other properties >> >> gpios = <&gpio 4 0 >> &gpio 5 0>; >> }; >> >> Is this kind of integration also possible? > > You can reference the gpio block via a phandle, e.g.: > > blockgpio { > compatible = "linux,gpio-block"; > > selector1 { > gpios = <&gpio 4 0>, > <&gpio 5 0>; > }; > }; > > powr@0x20 { > // ... > > gpios = <&selector1>; > }; > > > In the driver, you can get the gpio block like this: > > block = gpio_block_find_by_name(of_parse_phandle(powr, "gpios", 0)->name); > > (Simplified by removed error/NULL handling!) > > If this turns out to be a common pattern, I can add a convenience "get" > function for this.
Given the pick-up of device-tree in ARM and MIPS, I think this stands a good chance of becoming a common pattern. Do mind the "gpios" name; it's already used by the normal GPIO request functions...
This is one of the things I liked about my patch, there's little difference between using a group of GPIOs versus multiple separate GPIOs. The device-tree description is the same, only the driver handles them differently. You could ask the question whether the device-tree should make a difference between 1 GPIO, 2 separate GPIOs or 3 GPIOs in a block. For a H/W description language it's all the same. It is an implementation detail of the OS/drivers whether they handle them as a block or as separate GPIOs.
Regards, Stijn
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