linux-kernel - [RFC/RFT PATCH 0/3] gpiolib: make gpio irqchip compatible with sparse

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Date:   Sat, 8 Jul 2017 17:44:10 -0500
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Robert Jarzmik <robert.jarzmik@...e.fr>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-gpio@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Grygorii Strashko <grygorii.strashko@...com>
Subject: [RFC/RFT PATCH 0/3] gpiolib: make gpio irqchip compatible with sparse_irq

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