linux-kernel - Re: [PATCH] gpio: Remove dynamic allocation from populate_parent_alloc

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Date:   Fri, 13 May 2022 23:24:40 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, kernel-team@...roid.com,
        Daniel Palmer <daniel@...ngy.jp>,
        Romain Perier <romain.perier@...il.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Robert Richter <rric@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH] gpio: Remove dynamic allocation from populate_parent_alloc_arg()

On Thu, May 12, 2022 at 6:23 PM Marc Zyngier <maz@...nel.org> wrote:

> The gpiolib is unique in the way it uses intermediate fwspecs
> when feeding an interrupt specifier to the parent domain, as it
> relies on the populate_parent_alloc_arg() callback to perform
> a dynamic allocation.
>
> THis is pretty inefficient (we free the structure almost immediately),
> and the only reason this isn't a stack allocation is that our
> ThunderX friend uses MSIs rather than a FW-constructed structure.
>
> Let's solve it by providing a new type composed of the union
> of a struct irq_fwspec and a msi_info_t, which satisfies both
> requirements. This allows us to use a stack allocation, and we
> can move the handful of users to this new scheme.
>
> Also perform some additional cleanup, such as getting rid of the
> stub versions of the irq_domain_translate_*cell helpers, which
> are never used when CONFIG_IRQ_DOMAIN_HIERARCHY isn't selected.
>
> Tested on a Tegra186.
>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: Daniel Palmer <daniel@...ngy.jp>
> Cc: Romain Perier <romain.perier@...il.com>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Bartosz Golaszewski <brgl@...ev.pl>
> Cc: Thierry Reding <thierry.reding@...il.com>
> Cc: Jonathan Hunter <jonathanh@...dia.com>
> Cc: Robert Richter <rric@...nel.org>
> Cc: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
> Cc: Andy Gross <agross@...nel.org>
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>

This looks very appetizing to me but:

drivers/pinctrl/qcom/pinctrl-spmi-gpio.c | 15 ++++-----

This seems to have some changes to
->populate_parent_alloc_arg not even in linux-next,
so I get confused, what are the prerequisites? (Probably
something I already reviewed, but...)

Also: don't you also need to fix something in
drivers/pinctrl/qcom/pinctrl-ssbi-mpp.c?
the way I remember it it was quite similar to spmi-gpio
but I may be mistaken.

Yours,
Linus Walleij