linux-kernel - Re: [PATCH] gpio: Drop CONFIG_DEBUG

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Date:   Mon, 14 Mar 2022 23:22:46 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Brian Norris <briannorris@...omium.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Jianqun Xu <jay.xu@...k-chips.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: Drop CONFIG_DEBUG_GPIO

On Mon, Mar 14, 2022 at 4:00 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> On Fri, Mar 11, 2022 at 12:09 AM Brian Norris <briannorris@...omium.org> wrote:
> >
> > CONFIG_DEBUG_GPIO has existed since the introduction of gpiolib, but its
> > Kconfig description and motivation seem to have been off-base for quite
> > some time.
> >
> > Description: it says nothing about enabling extra printk()s. But -DDEBUG
> > does just that; it turns on every dev_dbg()/pr_debug() that would
> > otherwise be silent.
> >
> > Purpose: might_sleep() and WARN_ON() should have very low overhead, and
> > anyway, there's a separate CONFIG_DEBUG_ATOMIC_SLEEP for the
> > might_sleep() overhead.
> >
> > Additionally, the conflated purpose (extra debug checks, and extra
> > printing) makes for a mixed bag for users. In particular, some drivers
> > can be extra-spammy with -DDEBUG -- e.g., with the Rockchip GPIO driver
> > getting moved out of drivers/pinctrl/ in commit 936ee2675eee
> > ("gpio/rockchip: add driver for rockchip gpio"), now some dev_dbg()
> > calls are enabled in its IRQ handler.
> >
> > Altogether, it seems like CONFIG_DEBUG_GPIO isn't serving any good
> > purpose and should just be removed. It can be supplanted by dynamic
> > debug (which post-dates gpiolib) and atomic-debug facilities.
> >
> > Signed-off-by: Brian Norris <briannorris@...omium.org>
> > ---
> >
>
> I like it. It's true we don't see many of those DEBUG constructs
> anymore nowadays and overhead for might_sleep() and WARN_ON() is
> negligible.

I agree.  I have something similar for pinctrl, maybe that needs to
go too.

Yours,
Linus Walleij