linux-kernel - Re: [RFC/RFT 1/2] gpio/basic_mmio: add support for enable register

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Date:	Fri, 08 Jul 2011 07:23:55 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	"Nori, Sekhar" <nsekhar@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Hilman, Kevin" <khilman@...com>,
	"Chemparathy, Cyril" <cyril@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>
Subject: Re: [RFC/RFT 1/2] gpio/basic_mmio: add support for enable register

On 08/07/11 04:37, Grant Likely wrote:
> On Thu, Jul 07, 2011 at 10:15:31PM +0530, Nori, Sekhar wrote:
>> Hi Grant,
>>
>> On Thu, Jul 07, 2011 at 02:40:54, Grant Likely wrote:
>>> On Tue, Jul 05, 2011 at 04:15:44PM +1000, Ryan Mallon wrote:
>>>> On 05/07/11 15:10, Sekhar Nori wrote:
>>>>> Some GPIO controllers have an enable register
>>>>> which needs to be written to before a GPIO
>>>>> can be used.
>>>>>
>>>>> Add support for enabling the GPIO. At this
>>>>> time inverted logic for enabling the GPIO
>>>>> is not supported. This can be done by adding
>>>>> a disable register as and when a controller
>>>>> with this comes along.
>>>>>
>>>>> Signed-off-by: Sekhar Nori<nsekhar@...com>
>>>>> ---
>>>>>
>>>> <snip>
>>>>
>>>>> static int bgpio_setup_io(struct bgpio_chip *bgc,
>>>>>  			  void __iomem *dat,
>>>>> @@ -369,6 +401,7 @@ int __devinit bgpio_init(struct bgpio_chip *bgc,
>>>>>  			 void __iomem *clr,
>>>>>  			 void __iomem *dirout,
>>>>>  			 void __iomem *dirin,
>>>>> +			 void __iomem *en,
>>>>>  			 bool big_endian)
>>>> The arguments to this function are getting a bit unwieldy :-). Maybe
>>>> we need to introduce something like:
>>>>
>>>> struct bgpio_chip_info {
>>>>     struct device *dev;
>>>>     unsigned long sz;
>>>>     void __iomem *dat;
>>>>     void __iomem *set;
>>>>     void __iomem *clr;
>>>>     void __iomem *dirout;
>>>>     void __iomem *dirin;
>>>>     void __iomem *en;
>>>>     bool big_endian;
>>>> };
>>>>
>>>> and pass that to bgpio_init instead. It would have the added
>>>> benefits of making the drivers more readable and that
>>>> bgpio_chip_info structs in the drivers can probably be marked
>>>> __initdata also.
>>> Or, what may be better is to make callers directly update the
>>> bgpio_chip structure.
>> I started implementing it this way, but felt that the bgpio_chip
>> structure also has many internal members (like the spinlock) and
>> this method will require users to spend quite a bit of time figuring
>> out which structure members they should initialize and which to leave
>> for bgpio_init() to do for them.
>>
>> There is also the case of direction register which is set from
>> either dirout or dirin depending upon whether the logic is inverted
>> or not. The bgpio_chip however needs to deal with a single direction
>> register offset.
> We *absolutely* still need the helper function for the complex
> settings, but for the non-complex ones, I'd rather just directly
> access the structure.  The kerneldoc documentation of the structure
> can and should be explicit about what the caller is allowed to do.
>
You could pull out all of the user accessible parts the bgpio_chip
structure in to a structure called bgpio_chip_info (or whatever) that
the drivers fill in and pass to bgpio_init, which then gets assigned as
a member of bgpio_chip.

Not sure what you mean about the helper function. If bgpio_init takes a
structure with all of the information about the particular chip then
initialisation of either a simple or complex gpio chip is done using the
same function. Only the number of fields in the bgpio_chip_info
structure which need to be filled in should change.

~Ryan


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