linux-kernel - About devm_platform_ioremap_resource [Was: Re: [PATCH 01/32] pwm: sun4i: convert to devm_platform_ioremap

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Date:   Fri, 13 Nov 2020 08:03:43 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     alexandre.belloni@...tlin.com, heiko@...ech.de,
        Yangtao Li <tiny.windzz@...il.com>,
        nicolas.ferre@...rochip.com, matthias.bgg@...il.com,
        linux-riscv@...ts.infradead.org, festevam@...il.com,
        f.fainelli@...il.com, shc_work@...l.ru, khilman@...libre.com,
        ludovic.desroches@...rochip.com, jonathanh@...dia.com,
        linux-rockchip@...ts.infradead.org, wens@...e.org,
        bcm-kernel-feedback-list@...adcom.com, linux-imx@....com,
        slemieux.tyco@...il.com, linux-pwm@...r.kernel.org,
        rjui@...adcom.com, s.hauer@...gutronix.de, mripard@...nel.org,
        vz@...ia.com, linux-mediatek@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org, paul.walmsley@...ive.com,
        linux-tegra@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        Lee Jones <lee.jones@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, sbranden@...adcom.com,
        linux-kernel@...r.kernel.org, palmer@...belt.com,
        kernel@...gutronix.de, shawnguo@...nel.org,
        claudiu.beznea@...rochip.com, nsaenzjulienne@...e.de,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: About devm_platform_ioremap_resource [Was: Re: [PATCH 01/32] pwm:
 sun4i: convert to devm_platform_ioremap_resource]

Hello,

[Added lkml and the people involved in commit 7945f929f1a7
("drivers: provide devm_platform_ioremap_resource()") to Cc:. For the
new readers: This is about patches making use of
devm_platform_ioremap_resource() instead of open coding it. Full context
at https://lore.kernel.org/r/20201112190649.GA908613@ulmo]

On Thu, Nov 12, 2020 at 10:14:29PM +0100, Uwe Kleine-König wrote:
> On Thu, Nov 12, 2020 at 08:06:49PM +0100, Thierry Reding wrote:
> > I also think that it's overly narrow is scope, so you can't actually
> > "blindly" use this helper and I've seen quite a few cases where this was
> > unknowingly used for cases where it shouldn't have been used and then
> > broke things (because some drivers must not do the request_mem_region()
> > for example).
> 
> You have a link to such an accident?

I got a hint in private here: https://lore.kernel.org/r/1555670144-24220-1-git-send-email-aisheng.dong@nxp.com

devm_platform_ioremap_resource() is platform_get_resource() +
devm_ioremap_resource() and here it was used to replace
platform_get_resource() + devm_ioremap().

IMHO the unlucky thing in this situation is that devm_ioremap_resource()
and devm_ioremap() are different by more than just how they get the area
to remap. (i.e. devm_ioremap_resource() also does
devm_request_mem_region().)

So the problem is not the added wrapper, but unclear semantics in the
functions it uses. In my eyes devm_ioremap() and
devm_platform_ioremap_resource() should better be named
devm_request_ioremap() and devm_platform_request_ioremap_resource()
respectively. Is it worth to rename these for clearity?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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