Messages in this thread | | | Date | Fri, 19 Oct 2012 12:17:09 +0200 | Subject | Re: [PATCH 7/7] gpio/tegra: convert to use linear irqdomain | From | Linus Walleij <> |
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On Wed, Oct 17, 2012 at 8:32 PM, Stephen Warren <swarren@wwwdotorg.org> wrote: > On 10/16/2012 04:33 PM, Stephen Warren wrote: >> On 10/16/2012 01:23 PM, Linus Walleij wrote: >>> The MXS driver tries to do the work of irq_domain_add_linear() >>> by reserving a bunch of descriptors somewhere and keeping track >>> of the base offset, then calling irq_domain_add_legacy(). Let's >>> stop doing that and simply use the linear IRQ domain. >> >> This /looks/ fine, but appears to break users of GPIOs from this module, >> and causes a backtrace when cat /sys/kernel/debug/gpio: > ... > > The following additional diff makes it work: > >> diff --git a/drivers/gpio/gpio-tegra.c b/drivers/gpio/gpio-tegra.c >> index 0234162..c7c175a 100644 >> --- a/drivers/gpio/gpio-tegra.c >> +++ b/drivers/gpio/gpio-tegra.c >> @@ -460,7 +460,7 @@ static int __devinit tegra_gpio_probe(struct platform_device *pdev) >> gpiochip_add(&tegra_gpio_chip); >> >> for (gpio = 0; gpio < tegra_gpio_chip.ngpio; gpio++) { >> - int irq = irq_find_mapping(irq_domain, gpio); >> + int irq = irq_create_mapping(irq_domain, gpio); >> /* No validity check; all Tegra GPIOs are valid IRQs */ >> >> bank = &tegra_gpio_banks[GPIO_BANK(gpio)]; > > I wonder if perhaps the entirety of that loop and perhaps the one after > it should be in the IRQ domain's map op - is that how all this is > intended to work?
I've been asking the same kind of question...
Basically as far as I understand:
- If you use a linear IRQ domain you need to call irq_create_mapping() atleast once, and at that point the IRQ descriptor will be dynamically allocated. On subsequent calls, irq_find_mapping() can be used.
- If using legacy IRQ domains, descriptors are supposed to be allocated elsewhere, and you can just use irq_find_mapping(), but irq_create_mapping() does not hurt, because that call will check if a descriptor is already available.
- With the simple domain (as augmented by myself) the mappins will be dynamically created if the passed IRQ base is <= 0 else it falls through to creating a linear domain, so in this case to be certain irq_create_mapping() should also be called at least once.
I'm not overly happy with these semantics :-(
Basically irq_find_mapping() may be a fragile and dangerous optimization path.
I've folded the above into my patch.
Yours, Linus Walleij
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