linux-kernel - Re: [PATCH] [v2] Input: stmpe-ts - mark OF related data as maybe unused

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Message-ID: <6xoycaft6wnd4sm74f2o4koc7lvyl2mtxp2kc6lc4dzpjvby53@ejm5ssbfzbph>
Date: Tue, 25 Feb 2025 16:47:14 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, Arnd Bergmann <arnd@...db.de>, 
	Yu Jiaoliang <yujiaoliang@...o.com>, Oliver Graute <oliver.graute@...oconnector.com>, 
	linux-input@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] Input: stmpe-ts - mark OF related data as maybe
 unused

On Tue, Feb 25, 2025 at 03:53:26PM +0100, Arnd Bergmann wrote:
> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> 
> When compile tested with W=1 on x86_64 with driver as built-in:
> 
>   stmpe-ts.c:371:34: error: unused variable 'stmpe_ts_ids' [-Werror,-Wunused-const-variable]
> 
> Ideally this would be referenced from the platform_driver, but since
> the compatible string is already matched by the mfd driver for its
> parent device, that would break probing.
> 
> In this case, the of_device_id table just serves as a module alias
> for loading the driver, while the device itself is probed using
> the platform device name.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> Link: https://lore.kernel.org/lkml/20240403080702.3509288-8-arnd@kernel.org/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/input/touchscreen/stmpe-ts.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/touchscreen/stmpe-ts.c b/drivers/input/touchscreen/stmpe-ts.c
> index a94a1997f96b..3900aa2e3a90 100644
> --- a/drivers/input/touchscreen/stmpe-ts.c
> +++ b/drivers/input/touchscreen/stmpe-ts.c
> @@ -366,7 +366,7 @@ static struct platform_driver stmpe_ts_driver = {
>  };
>  module_platform_driver(stmpe_ts_driver);
>  
> -static const struct of_device_id stmpe_ts_ids[] = {
> +static const struct of_device_id stmpe_ts_ids[] __maybe_unused = {
>  	{ .compatible = "st,stmpe-ts", },
>  	{ },
>  };

Following this we have

	MODULE_DEVICE_TABLE(of, stmpe_ts_ids);

.

With 

diff --git a/include/linux/module.h b/include/linux/module.h
index 30e5b19bafa9..014f033ef1ba 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -250,7 +250,8 @@ extern void cleanup_module(void);
 extern typeof(name) __mod_device_table__##type##__##name		\
   __attribute__ ((unused, alias(__stringify(name))))
 #else  /* !MODULE */
-#define MODULE_DEVICE_TABLE(type, name)
+#define MODULE_DEVICE_TABLE(type, name)					\
+static const typeof(name) *__mod_device_table__##type##__##name##_ptr __attribute__((unused)) = &(name)
 #endif
 
 /* Version of form [<epoch>:]<version>[-<extra-version>].

the warning goes away and stmpe_ts_ids isn't included in the .o file
without having to add __maybe_unused to the driver.

I would consider that a superior approach.

Best regards
Uwe

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