linux-kernel - Re: [PATCH] clk: imx8mp: register driver at arch

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Date:   Sat, 19 Nov 2022 22:57:02 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Fabio Estevam <festevam@...il.com>
Cc:     Abel Vesa <abelvesa@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH] clk: imx8mp: register driver at arch_initcall time

On 19/11/2022 22.38, Fabio Estevam wrote:
> On Wed, Sep 28, 2022 at 9:41 AM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> We have an imx8mp-based board with an external gpio-triggered
>> watchdog. Currently, we don't get to handle that in time before it
>> resets the board.
>>
>> The probe of the watchdog device gets deferred because the SOC's GPIO
>> controller is not yet ready, and the probe of that in turn gets deferred
>> because its clock provider (namely, this driver) is not yet
>> ready. Altogether, the watchdog does not get handled until the late
>> initcall deferred_probe_initcall has made sure all leftover devices
>> have been probed, and that's way too late.
>>
>> Aside from being necessary for our board, this also reduces total boot
>> time because fewer device probes get deferred.
>>
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>> ---
>> It would probably be reasonable to do the same to the other imx8m* clk
>> drivers, but I don't have any such hardware to test on.
> 
> Agreed.
> 
>> +static void __exit imx8mp_clk_exit(void)
>> +{
>> +       platform_driver_unregister(&imx8mp_clk_driver);
>> +}
>> +module_exit(imx8mp_clk_exit);
> 
> Isn't module_exit() unnecessary here, since we pass suppress_bind_attrs = true?

Sorry, I don't follow. Before this patch, the driver also implicitly had
a module_exit() doing exactly this platform_driver_unregister(), it was
just hidden inside the module_platform_driver() macro. And I think
that's necessary if one wants to test that the module can be loaded and
unloaded (I don't think it's ever useful or even possible to have it be
a module on an actual imx8mp board).

For a modular build, this patch changes nothing since all foo_initcall
levels are translated to module_initcall for those. And when the driver
is built-in, the __exit code, both before and after this patch, is
discarded in the final image.

Rasmus