Message-ID: <4FBDBC2B.3090300@wwwdotorg.org>
Date:	Wed, 23 May 2012 22:42:19 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Dong Aisheng <dongas86@...il.com>
CC:	Dong Aisheng <b29396@...escale.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linus.walleij@...ricsson.com,
	devicetree-discuss <devicetree-discuss@...ts.ozlabs.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support

On 05/23/2012 07:42 PM, Dong Aisheng wrote:
> On Thu, May 24, 2012 at 4:44 AM, Stephen Warren <swarren@...dotorg.org> wrote:
>> On 05/23/2012 07:22 AM, Dong Aisheng 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_offset $pin_offset $npin>.
>>>
>>> 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>
>>
>> This is mostly good. Just a few comments:
>>
>>> +gpio-maps: 4 integers array, each entry in the array represents a gpio
>>> +range with the format: <&gpio $gpio_offset $pin_offset $count>
>>> +- gpio: phandle pointing at gpio device node
>>> +- gpio_offset: integer, the local offset of $gpio
>>> +- pin_offset: integer, the pin offset or pin id
>>> +- npins: integer, the gpio ranges starting from pin_offset
>>
>> This uses a single cell to represent a GPIO ID within a GPIO controller.
>> The standard GPIO bindings use #gpio-cells, where that's a property in
>> the GPIO controller's node. I wonder if we shouldn't do the same here,
>> and call into the GPIO driver to parse #gpio-cells and give back the
>> Linux GPIO ID, just like of_get_named_gpio_flags() does. This would also
>> make this code able to cope with the GPIO of_xlate function returning a
>> different GPIO chip, which Grant put in place for banked GPIO controllers.
>>
> I checked the code, the second cell only represents gpio flag in
> of_gpio_simple_xlate which seems meaningless to pinctrl, so it looks
> increase overhead to pinctrl gpio ranges map.

With the simple translation function, yes it's just flags. However, not
all GPIO controllers use the simple translation function; I think I
recall the Exynos binding having 4 or 5 cells. In other words, the
format is defined by each individual GPIO controller, even if many/most
do happen to follow the same format.

> However, it seems i may have to agree that we need keep align with the
> exist of gpio design to use the standard way to get gpio number via
> of_xlate function rather than do it privately in pinctrl driver.
> 
> One disadvantage is that i can not reuse of_get_named_gpio_flags due
> to different format
> for gpio-maps, i may have to write a slightly different one as
> of_get_named_gpio_flags
> for gpio-maps.
> 
>>> diff --git a/drivers/pinctrl/devicetree.c b/drivers/pinctrl/devicetree.c
>>
>>> +int pinctrl_dt_add_gpio_ranges(struct pinctrl_dev *pctldev,
>>
>> The locking I was talking about before is between the following line:
>>
>>> +             ranges[i].gc = of_node_to_gpiochip(np_gpio);
>>
>> and this code:
>>
>>> +             ranges[i].name = dev_name(pctldev->dev);
>>> +             ranges[i].base = ranges[i].gc->base + gpio_offset;
>>> +             ranges[i].pin_base = pin_offset;
>>> +             ranges[i].npins = npins;
>>
>> If of_node_to_gpiochip() doesn't mark the GPIO chip as "in use", then
>> the module that provides that device could be unloaded between the two
>> blocks of code above.
>>
> Correct.
> 
>> Re: your locking comments in your other email: ranges[i].gc doesn't
>> appear to be used anywhere else in pinctrl, so I think it's OK not to
>> lock the GPIO chip for any more time than between the above two blocks
>> of code.
>>
> So i will add lock between them like:
> ranges[i].gc = of_node_to_gpiochip(np_gpio);
> if (!try_module_get(ranges[i].gc->owner))
>     err...

I think that module_get() needs to happen inside of_node_to_gpiochip(),
so that it executes inside any lock that function takes.

> ranges[i].name = dev_name(pctldev->dev);
> ranges[i].base = ranges[i].gc->base + gpio_offset;
> ranges[i].pin_base = pin_offset;
> ranges[i].npins = npins;
> module_put(ranges[i].gc->owner)
> If anything wrong please let me know.
> 
>> Finally, just a minor nit:
>>
>>> +             ranges[i].gc = of_node_to_gpiochip(np_gpio);
>>> +             if (!ranges[i].gc) {
>>> +                     dev_err(pctldev->dev,
>>> +                             "can not find gpio chip of node(%s)\n",
>>> +                             np_gpio->name);
>>> +                     of_node_put(np_gpio);
>>> +                     return -EPROBE_DEFER;
>>> +             }
>>> +
>>> +             of_node_put(np_gpio);
>>
>> could be slightly simpler:
>>
>> +               ranges[i].gc = of_node_to_gpiochip(np_gpio);
>> +               of_node_put(np_gpio); <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>> +               if (!ranges[i].gc) {
>> +                       dev_err(pctldev->dev,
>> +                               "can not find gpio chip of node(%s)\n",
>> +                               np_gpio->name);
> Because here still uese np_gpio,  Can i still use it after of_node_put?

Oh right, that makes sense, yes.
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