linux-kernel - Re: [PATCH] gpiolib: fix chip->base handling in of_gpio_simple

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Message-ID: <500EBDA4.6020104@gmail.com>
Date:	Tue, 24 Jul 2012 17:22:12 +0200
From:	Daniel Mack <zonque@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...ricsson.com>
Subject: Re: [PATCH] gpiolib: fix chip->base handling in of_gpio_simple_xlate()

On 24.07.2012 16:08, Arnd Bergmann wrote:
> On Tuesday 24 July 2012, Daniel Mack wrote:

>>>>> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
>>>>> index d18068a..51bc232 100644
>>>>> --- a/drivers/gpio/gpiolib-of.c
>>>>> +++ b/drivers/gpio/gpiolib-of.c
>>>>> @@ -147,13 +147,13 @@ int of_gpio_simple_xlate(struct gpio_chip *gc,
>>>>>     if (WARN_ON(gpiospec->args_count < gc->of_gpio_n_cells))
>>>>>             return -EINVAL;
>>>>>  
>>>>> -   if (gpiospec->args[0] >= gc->ngpio)
>>>>> +   if (gpiospec->args[0] >= gc->ngpio + gc->base)
>>>>>             return -EINVAL;
>>>>>  
>>>>>     if (flags)
>>>>>             *flags = gpiospec->args[1];
>>>>>  
>>>>> -   return gpiospec->args[0];
>>>>> +   return gpiospec->args[0] - gc->base;
>>>>>  }
>>>>>  EXPORT_SYMBOL(of_gpio_simple_xlate);
>>>
>>> Where would that gc->base come from?
>>
>> It is set up when the chips are initialized. Let's put it that way: why
>> would we have this ->base if it is practically unusable in devicetree
>> environments?
> 
> The base gets used to put the gpiochip into the Linux gpio number space,
> which is not necessarily the same as the number space used in the device
> tree. You can dynamically add other gpio controllers that would get
> some arbitrary base assigned at runtime, so you cannot subtract that
> base from the hardware number to get a local one in the common code.
> 
> I fear you will have to provide your own xlate function for pxa if
> you want to use this numbering. Something like this:?

I did my own xlate function in the first place, but then I thought it
could be made working in a more general way. But your explanation makes
sense, so I will add something that is based on your sniplet.

Thanks,
Daniel
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