On Fri, Aug 05, 2011 at 08:43:20AM -0700, Stephen Warren wrote:
Russell King - ARM Linux wrote at Friday, August 05, 2011 3:40 AM:
On Thu, Aug 04, 2011 at 05:00:17PM -0600, Stephen Warren wrote:
In http://www.spinics.net/lists/linux-tegra/msg01731.html, Mark Brown pointed out that it was a little silly forcing every board or driver to gpio_request() a GPIO that is later converted to an IRQ, and passed to request_irq. The first patch in this series instead makes the core IRQ code perform these calls when appropriate, to avoid duplicating it everywhere.
Trying to go from IRQ to GPIO is not a good idea - most of the IRQ <-> GPIO macros we have today are just plain broken. Many of them just add or subtract a constant, which means non-GPIO IRQs have an apparant GPIO number too. Couple this with the fact that all positive GPIO numbers are valid, and this is a recipe for wrong GPIOs getting used and GPIOs being requested for non-GPIO IRQs.
I think this was also discussed in the past, and the conclusion was that IRQs should be kept separate from GPIOs. Maybe views have changed since then...
However, if we do want to do this, then it would be much better to provide a new API for requesting GPIO IRQs, eg:
gpio_request_irq()
which would wrap around request_threaded_irq(), takes a GPIO number, does the GPIO->IRQ conversion internally, and whatever GPIO setup is required. Something like this:
With that approach, drivers need to explicitly know whether they're passed a GPIO or an IRQ, and do something different, or they need to choose to only accept a GPIO or IRQ.
You completely missed the biggest reason why your approach is broken.
+ gpio = irq_to_gpio(irq); + if (gpio_is_valid(gpio))
Let's look at the code:
#define ARCH_NR_GPIOS 256
static inline bool gpio_is_valid(int number) { return number >= 0 && number < ARCH_NR_GPIOS; }
Now, let's take AT91:
#define irq_to_gpio(irq) (irq)
This doesn't define ARCH_NR_GPIOS, so it gets the default 256. Now lets take a random selection of the AT91 interrupt numbers:
#define AT91RM9200_ID_US3 9 /* USART 3 */ #define AT91RM9200_ID_MCI 10 /* Multimedia Card Interface */ #define AT91RM9200_ID_UDP 11 /* USB Device Port */ #define AT91RM9200_ID_TWI 12 /* Two-Wire Interface */ #define AT91RM9200_ID_SPI 13 /* Serial Peripheral Interface */ #define AT91RM9200_ID_SSC0 14 /* Serial Synchronous Controller 0 */ #define AT91RM9200_ID_SSC1 15 /* Serial Synchronous Controller 1 */
None of these are GPIOs. Yet gpio_is_valid(irq_to_gpio(AT91RM9200_ID_TWI)) is true.
That's the problem - it's undefined whether gpio_is_valid(irq_to_gpio(irq)) returns true or false for any particular interrupt. There's no multiplexing through gpiolib for the IRQ-to-GPIO mapping either, so it doesn't work for off-SoC GPIOs.
So, you can't reliably go from interrupt numbers to GPIO numbers - it's just not supported. So to throw this into the IRQ layer is just going to end up breaking a hell of a lot of platforms.
Now, stack on top of that a discussion at the Linaro Connect conference this week where we discussed getting rid of IRQ numbers entirely, and our desire to kill off irq_to_gpio() and I think it makes this approach a non-starter.
So it seems like, as was mentioned elsewhere in this thread, the upshot of this conversation is that interrupt chip drivers should do this internally, both to avoid requiring a general irq_to_gpio function, and because calling gpio_direction_input for GPIOs-used-as-IRQs isn't appropriate for all hardware.
That would be more appropriate, because the IRQ chip stuff at least knows if there's a GPIO associated with it.
There's still the unanswered question whether we even want the IRQ layer to do this kind of stuff, and the previous decision on that I believe was in the negative. So I think Thomas needs to respond to that point first.