Subject: [PATCH 3/5] gpio/omap: Add DT support to GPIO driver

From: [email-masked] (Jon Hunter)
Date: Tue, 16 Apr 2013 21:00:15 -0500

On 04/16/2013 07:41 PM, Javier Martinez Canillas wrote:
> On Wed, Apr 17, 2013 at 1:14 AM, Jon Hunter <[email-masked]> wrote:
>>
>> On 04/16/2013 05:11 PM, Stephen Warren wrote:
>>> On 04/16/2013 01:27 PM, Jon Hunter wrote:
>>>>
>>>> On 04/16/2013 01:40 PM, Stephen Warren wrote:
>>>>> On 04/15/2013 05:04 PM, Jon Hunter wrote:
>>> ...
>>>>>> If some driver is calling gpio_request() directly, then they will most
>>>>>> likely just call gpio_to_irq() when requesting the interrupt and so the
>>>>>> xlate function would not be called in this case (mmc drivers are a good
>>>>>> example). So I don't see that as being a problem. In fact that's the
>>>>>> benefit of this approach as AFAICT it solves this problem.
>>>>>
>>>>> Oh. That assumption seems very fragile. What about drivers that actually
>>>>> do have platform data (or DT bindings) that provide both the IRQ and
>>>>> GPIO IDs, and hence don't use gpio_to_irq()? That's entirely possible.
>>>>
>>>> Right. In the DT case though, if someone does provide the IRQ and GPIO
>>>> IDs then at least they would use a different xlate function. Another
>>>> option to consider would be defining the #interrupt-cells = <3> where we
>>>> would have ...
>>>>
>>>> cell-#1 --> IRQ domain ID
>>>> cell-#2 --> Trigger type
>>>> cell-#3 --> GPIO ID
>>>>
>>>> Then we could have a generic xlate for 3 cells that would also request
>>>> the GPIO. Again not sure if people are against a gpio being requested in
>>>> the xlate but just an idea. Or given that irq_of_parse_and_map() calls
>>>> the xlate, we could have this function call gpio_request() if the
>>>> interrupt controller is a gpio and there are 3 cells.
>>>
>>> I rather dislike this approach since:
>>>
>>> a) It requires changes to the DT bindings, which are already defined.
>>> Admittedly it's backwards-compatible, but still.
>>>
>>> b) There isn't really any need for the DT to represent this; the
>>> GPIO+IRQ driver itself already knows which IRQ ID is which GPIO ID and
>>> vice-versa (if the HW has such a concept), so there's no need for the DT
>>> to contain this information. This seems like pushing Linux's internal
>>> requirements into the design of the DT binding.
>>
>> Yes, so the only alternative is to use irq_to_gpio to avoid this.
>>
>>> c) I have the feeling that hooking the of_xlate function for this is a
>>> bit of an abuse of the function.
>>
>> I was wondering about that. So I was grep'ing through the various xlate
>> implementations and found this [1]. Also you may recall that in the
>> of_dma_simple_xlate() we call the dma_request_channel() to allocate the
>> channel, which is very similar. However, I don't wish to get a
>> reputation as abusing APIs so would be good to know if this really is
>> abuse or not ;-)
>>
>> Cheers
>> Jon
>>
>> [1] http://permalink.gmane.org/gmane.linux.ports.arm.kernel/195124
> 
> I was looking at [1] shared by Jon and come up with the following
> patch that does something similar for OMAP GPIO. This has the
> advantage that is local to gpio-omap instead changing gpiolib-of and
> also doesn't require DT changes
> 
> But I don't want to get a reputation for abusing APIs neither :-)
> 
> Best regards,
> Javier
> 
> From 23368eb72b125227fcf4b22be19ea70b4ab94556 Mon Sep 17 00:00:00 2001
> From: Javier Martinez Canillas <[email-masked]>
> Date: Wed, 17 Apr 2013 02:03:08 +0200
> Subject: [PATCH 1/1] gpio/omap: add custom xlate function handler
> 
> Signed-off-by: Javier Martinez Canillas <[email-masked]>
> ---
>  drivers/gpio/gpio-omap.c |   29 ++++++++++++++++++++++++++++-
>  1 files changed, 28 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
> index 8524ce5..77216f9 100644
> --- a/drivers/gpio/gpio-omap.c
> +++ b/drivers/gpio/gpio-omap.c
> @@ -1097,6 +1097,33 @@ static void omap_gpio_chip_init(struct gpio_bank *bank)
>  static const struct of_device_id omap_gpio_match[];
>  static void omap_gpio_init_context(struct gpio_bank *p);
> 
> +static int omap_gpio_irq_domain_xlate(struct irq_domain *d,
> +				      struct device_node *ctrlr,
> +				      const u32 *intspec, unsigned int intsize,
> +				      irq_hw_number_t *out_hwirq,
> +				      unsigned int *out_type)
> +{
> +	int ret;
> +	struct gpio_bank *bank = d->host_data;
> +	int gpio = bank->chip.base + intspec[0];
> +
> +	if (WARN_ON(intsize < 2))
> +		return -EINVAL;
> +
> +	ret = gpio_request_one(gpio, GPIOF_IN, ctrlr->full_name);
> +	if (ret)
> +		return ret;
> +
> +	*out_hwirq = intspec[0];
> +	*out_type = (intsize > 1) ? intspec[1] : IRQ_TYPE_NONE;
> +
> +	return 0;
> +}
> +
> +static struct irq_domain_ops omap_gpio_irq_ops = {
> +	.xlate	= omap_gpio_irq_domain_xlate,
> +};
> +
>  static int omap_gpio_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -1144,7 +1171,7 @@ static int omap_gpio_probe(struct platform_device *pdev)
> 
> 
>  	bank->domain = irq_domain_add_linear(node, bank->width,
> -					     &irq_domain_simple_ops, NULL);
> +					     &omap_gpio_irq_ops, bank);
>  	if (!bank->domain)
>  		return -ENODEV;
> 

That would work for omap, in fact I posted pretty much the same thing a
day ago [1] ;-)

I was trying to see if we could find a common solution that everyone
could use as it seems that ideally we should all be requesting the gpio.

Cheers
Jon

[1] http://marc.info/?l=linux-arm-kernel&m=136606204823845&w=1