Message-ID: <CAA+hA=QT83wqe8MOi4B4xY4zTGbQPVhKxwuU_A+cPg-U3JicGw@mail.gmail.com>
Date:	Sat, 26 May 2012 09:58:06 -0700
From:	Dong Aisheng <dongas86@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Dong Aisheng <b29396@...escale.com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linus.walleij@...ricsson.com,
	swarren@...dotorg.org, devicetree-discuss@...ts.ozlabs.org,
	rob.herring@...xeda.com
Subject: Re: [PATCH v4 6/6] pinctrl: add pinctrl gpio binding support

On Fri, May 25, 2012 at 5:29 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
> On Fri, 25 May 2012 21:36:20 +0800, Dong Aisheng <b29396@...escale.com> wrote:
>> From: Dong Aisheng <dong.aisheng@...aro.org>
>>
>> This patch implements a standard common binding for pinctrl gpio ranges.
>> Each SoC can add gpio ranges through device tree by adding a gpio-maps property
>> under their pinctrl devices node with the format:
>> <&gpio $gpio-specifier $pin_offset $count>
>> while the gpio phandle and gpio-specifier are the standard approach
>> to represent a gpio in device tree.
>> Then we can cooperate it with the gpio xlate function to get the gpio number
>> from device tree to set up the gpio ranges map.
>>
>> Then the pinctrl driver can call pinctrl_dt_add_gpio_ranges(pctldev, node)
>> to parse and register the gpio ranges from device tree.
>>
>> Signed-off-by: Dong Aisheng <dong.aisheng@...aro.org>
>> ---
>> Personally i'm not very satisfied with current solution due to a few reasons:
>> 1) i can not user standard gpio api to get gpio number
>> 2) i need to reinvent a new api of_parse_phandles_with_args_ext which i'm not
>> sure if it can be accepted by DT maintainer.
>
> Right, as mentioned in my other email, doing it this way completely
> breaks the way the phandle-with-args pattern works.  That pattern
> depends on the phandle node to have a #-cells property telling it how
> many cells to process for the binding.  Adding additional data cells
> means the kernel is no longer able to parse multiple entries in the
> gpios property.
Hmm, it can still parse multiple entries in the gpios property except
that it adds two args although it's not related to gpio, but it is useful
for users for special case like pinctrl gpio ranges map.

>
>> If i did not invent that API, i need to rewrite a lot of duplicated code
>> with slight differences with the exist functions like of_get_named_gpio_flags
>> and of_parse_phandle_with_args for the special pinctrl gpio maps format.
>>
>> So i just sent it out first to see people's comment and if any better solution.
>>
>> One alternative solution is that that the gpio-maps into two parts:
>> pinctrl-gpios = <&gpio_phandle gpio-specifier ..>
>> pinctrl-gpio-maps = <pin_id count ..>
>> Then we can reuse the standard gpio api altough it's not better than the
>> original one.
>>
>> Comments are welcome!
>>
>> ChangeLog v3->v4:
>> * using standard gpio parsing approach to get the gpio number from device
>>   tree. The gpio-maps becomes a little slightly different as before:
>>   <&gpio $gpio_specifier $pin_offset $npin>.
>>   The $gpio_specifier length is controller dependent which is specified by
>>   '#gpio-cells' in in gpio controller node.
>>
>> ChangeLog v2->v3:
>> * standardise the gpio ranges node name to 'gpio-maps'. Each SoC should use this
>> node name to define gpio ranges.
>> * defer probe if can not get gpiochip from node in case gpio driver is still
>> not loaded.
>> * some other minor fixes suggested by Stephen Warren.
>>
>> ChangeLog v1->v2:
>> * introduce standard binding for gpio range.
>> ---
>>  .../bindings/pinctrl/pinctrl-bindings.txt          |   22 +++++
>>  drivers/pinctrl/devicetree.c                       |   95 ++++++++++++++++++++
>>  include/linux/pinctrl/pinctrl.h                    |   11 +++
>>  3 files changed, 128 insertions(+), 0 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> index c95ea82..e999be5 100644
>> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> @@ -126,3 +126,25 @@ device; they may be grandchildren, for example. Whether this is legal, and
>>  whether there is any interaction between the child and intermediate parent
>>  nodes, is again defined entirely by the binding for the individual pin
>>  controller device.
>> +
>> +=== pinctrl gpio ranges ===
>> +Some pins in pinctrl device can also be multiplexed as gpio. With a gpio range
>> +map, user can know which pin in the range can be used as gpio.
>> +
>> +Required properties:
>> +gpio-maps: integers array, each entry in the array represents a gpio range
>> +with the format: <&gpio $gpio-specifier $pin_offset $count>
>> +- gpio: phandle pointing at gpio device node
>> +- gpio-specifier: array of #gpio-cells specifying specific gpio, the length is
>> +  controller specific. Usually it may be two cells for simple gpio.
>> +- pin_offset: integer, the pin offset or pin id
>> +- npins: integer, the gpio ranges starting from pin_offset
>> +
>> +For example:
>> +pincontroller {
>> +     /* gpio-specifier is two cells */
>> +     gpio-maps = <&gpio1 0 0 0 32
>> +                  &gpio2 0 0 0 30
>> +                  &gpio3 1 0 100 1
>> +                  ....>;
>
> Hmmm.... I need more information about this gpio-maps property.  How
> is it arranged?  What kind of data is in it.  Can you give some
> specific examples of how hardware would be described with a gpio-maps
> property?
>
For exampe:
MX6Q_PAD_SD2_DAT2__GPIO_1_13 means MX6Q_PAD_SD2_DAT2 can be used as GPIO_1_13,
For reference gpio1,13, we usually do: xx-gpios = <gpio1 13 0> in device tree.
Here we want to create a pin map of gpio1,13 to MX6Q_PAD_SD2_DAT2 for
pinctrl gpio ranges map,
the format should be <GPIO_NUMBER PIN_ID NPINS>, then the pinctrl core
can automatically mux
the PIN_ID to gpio function by refer to this map.
For GPIO_NUMBER, we want to use the standard gpio dt represent way
since the gpio base may
be dynamically.
Assume MX6Q_PAD_SD2_DAT2 pin id is 1 and only one pin starting from it
can be used as gpio.
Then the gpio-maps for MX6Q_PAD_SD2_DAT2 can be:
gpio-maps = <gpio1 13 0 1 1>

We may have several pins can be used as gpio on mx6q.
Then the gpio-maps may becomes:
gpio-maps = <gpio1 13 0 1 1>,
                   <gpio1 14 0 5 1>,
                   <gpio2 0 0 20 1>,
                   ................

Since the format is a little different from the standard gpio
represent way, so i can not use the standard gpio
api to parse the gpio number. That's why i need to invent
of_parse_phandle_args_ext function for this special
format.

we still did not find any better way to do that.
Do you have any suggestion for this special case?

Regards
Dong Aisheng
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