linux-kernel - Re: [RFT PATCH v2] gpiolib: allow gpio irqchip to map irqs dynamically

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Date:   Tue, 1 Aug 2017 09:52:30 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Grygorii Strashko <grygorii.strashko@...com>,
        Bartosz Golaszewski <brgl@...ev.pl>
Cc:     "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [RFT PATCH v2] gpiolib: allow gpio irqchip to map irqs dynamically

On Fri, Jul 21, 2017 at 6:49 PM, Grygorii Strashko
<grygorii.strashko@...com> wrote:

> Now IRQ mappings are always created for all (allowed) GPIOs in gpiochip in
> gpiochip_irqchip_add_key() which goes against the idea of SPARSE_IRQ and,
> as result, leads to:
>  - increasing of memory consumption for IRQ descriptors most of which will
> never ever be used (espessially on platform with a high number of GPIOs).
> (sizeof(struct irq_desc) == 256 on my tested platforms)
>  - imposibility to use GPIO irqchip APIs by gpio drivers when HW implements
> GPIO IRQ functionality as IRQ crossbar/router 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
>   Mem savings 267*256 = 68352 (66kB)
> - am335x-evm: number of created irq mappings decreased from 188 -> 63
>   Mem savings 125*256 = 32000 (31kB)
>
> [1] https://lkml.org/lkml/2017/6/15/428
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---
> Changes in v2:
> - restored struct gpio_chip->irq_base to fix buld of gpio-mockup.c

Applied this rather than v1.

But maybe we should get rid of ->irq_base from gpio-mockup.c
and delete it, as the base is irqchip-internal.

Bartosz what do you say? Do we need this in the mockup?

Yours,
Linus Walleij