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Subject[RFC/RFT PATCH 0/3] gpiolib: make gpio irqchip compatible with sparse_irq
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The idea of this changes was inspired by discussion [1].

Now IRQ mappings are always created for all (allowed) GPIOs in GPIO irqchip in
gpiochip_irqchip_add_key() and this goes against the idea of SPARSE_IRQ and,
as result, leads to:
- increasing of memory consumption because of allocated IRQ descriptors most
of which will never ever be used (especially on platform with a
high number of GPIOs).
- imposibility to use GPIO irqchip APIs by gpio drivers when HW implements
GPIO IRQ functionality as IRQ crossbar/multiplexer which has only limited
number of IRQ outputs (example from [1], all GPIOs can be mapped on only 8
IRQs).

Hence, remove static IRQ mapping code from gpiochip_irqchip_add_key() and
instead replace irq_find_mapping() with irq_create_mapping() in
gpiochip_to_irq(). Also add additional gpiochip_irqchip_irq_valid() calls
in gpiochip_to_irq() and gpiochip_irq_map().

After this change gpio2irq mapping will happen the following way when GPIO
irqchip APIs are used by gpio driver:
- IRQ mappings will be created statically if driver passes first_irq>0
vlaue in gpiochip_irqchip_add_key().
- IRQ mappings will be created dynamically from gpio_to_irq() or
of_irq_get().

Tested on am335x-evm and dra72-evm-revc.
- dra72-evm-revc: number of created irq mappings decreased from 402 -> 135
- am335x-evm: number of created irq mappings decreased from 188 -> 63

It's good to have more testing feedbacks for these patches
(personally I do not expect regressions, but who knows). One possible side
effect is "Cannot allocate irq_descs @ IRQ%d, assuming pre-allocated\n" message
during boot, but in this case it might be good to take a look on such GPIO
drivers to understand why they need to allocate IRQ descriptors.

[1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1435847.html

Grygorii Strashko (3):
gpio: tegra: remove gpio_to_irq() from hw irq handlers
gpio: pxa: remove gpio_to_irq() from hw irq handlers
gpiolib: make gpio irqchip compatible with sparse_irq

drivers/gpio/gpio-pxa.c | 8 +++++---
drivers/gpio/gpio-tegra.c | 3 ++-
drivers/gpio/gpiolib.c | 29 ++++++-----------------------
include/linux/gpio/driver.h | 1 -
4 files changed, 13 insertions(+), 28 deletions(-)

--
2.10.1

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