linux-kernel - Re: [PATCH 1/4] Make non-linear GPIO ranges accesible from gpiolib

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Message-ID: <51C1F531.3050205@wwwdotorg.org>
Date:	Wed, 19 Jun 2013 12:15:13 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Christian Ruppert <christian.ruppert@...lis.com>,
	Patrice CHOTARD <patrice.chotard@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Sascha Leuenberger <sascha.leuenberger@...lis.com>,
	Pierrick Hascoet <pierrick.hascoet@...lis.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH 1/4] Make non-linear GPIO ranges accesible from gpiolib

On 06/19/2013 06:03 AM, Linus Walleij wrote:
> On Tue, Jun 18, 2013 at 11:29 AM, Christian Ruppert
> <christian.ruppert@...lis.com> wrote:
> 
>> This patch adds the infrastructure required to register non-linear gpio
>> ranges through gpiolib and the standard GPIO device tree bindings.
>>
>> Signed-off-by: Christian Ruppert <christian.ruppert@...lis.com>
> 
> I'm basically fine with this, but would like Stephen's ACK if possible.
> 
>> +In addition, named groups of pins can be mapped to pin groups of a given
>> +pin controller:
>> +
>> +       gpio_pio_g: gpio-controller@...0 {
>> +               #gpio-cells = <2>;
>> +               compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
>> +               reg = <0x1480 0x18>;
>> +               gpio-controller;
>> +               gpio-ranges = <&pinctrl1 0 0 0>, <&pinctrl2 3 0 0>;
>> +               gpio-ranges-group-names = "foo", "bar";
>> +       };
>> +
>> +where,
>> +   &pinctrl1 and &pinctrl2 is the phandle to the pinctrl DT node.
>> +
>> +   The following value specifies the base GPIO offset of the pin range with
>> +   respect to the GPIO controller's base. The remaining two values must be
>> +   0 to indicate that a named pin group should be used for the respective
>> +   range. The number of pins in the range is the number of pins in the pin
>> +   group.
> 
> So while this works, these zeroes seem a bit awkward, but maybe
> it's the only way?
> 
> I'm not good enough on device tree conventions, but isn't this possible:
> 
>               gpio-ranges = <&pinctrl1 0>, <&pinctrl2 3>;
>               gpio-ranges-group-names = "foo", "bar";
> 
> Since we don't have any #gpio-ranges-cells or anything like that I
> guess we can define this to have a flexible number of cells
> depending on use case?

If we're willing to have gpio-ranges be either *all* group names, or
*all* IDs, we can define the format of gpio-ranges to have two cells
(phandle and GPIO number) if the property gpio-ranges-group-names
exists, but four cells (phandle, GPIO number, pin number, count)
otherwise. However, that's a little restrictive, since then what if one
GPIO controller is hooked to two different pinmux controllers, and you
want to use different formats for the references to each. A
#gpio-ranges-cells in the target of the phandle would allow this, but I
don't think this is something the pinctrl node should dictate to those
who reference it; it's quite legitimate for a GPIO node to use the pure
numeric mapping even if the pin controller happens to expose some pin
groups that allow you to do the mapping by name.
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