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

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Date:   Tue, 1 Aug 2017 09:46:03 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     Robert Jarzmik <robert.jarzmik@...e.fr>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [RFC/RFT PATCH 3/3] gpiolib: make gpio irqchip compatible with sparse_irq

On Sun, Jul 9, 2017 at 12:44 AM, Grygorii Strashko
<grygorii.strashko@...com> wrote:

> Now IRQ mappings are always created for all (allowed) GPIOs in gpio irqchip in
> gpiochip_irqchip_add_key() which 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().
>
> [1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1435847.html
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>

This is obviously better and what I should have done from the beginning
had I only been smart enough, so what better to do than to throw this in
now for -next and see what happens :)

Patch applied.

Yours,
Linus Walleij