linux-kernel - Re: [PATCH -next] drm/bridge: fix -Wunused-const-variable= warning

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Date:   Wed, 26 Jul 2023 12:54:36 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Zhu Wang <wangzhu9@...wei.com>
Cc:     andrzej.hajda@...el.com, neil.armstrong@...aro.org,
        rfoss@...nel.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com,
        daniel@...ll.ch, javierm@...hat.com, dianders@...omium.org,
        benjamin.mugnier@...s.st.com, kabel@...nel.org, anarsoul@...il.com,
        duwe@...e.de, mripard@...nel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH -next] drm/bridge: fix -Wunused-const-variable= warning

[Cc += Arnd, Andy who did similar changes in the past]

Hello,

On Wed, Jul 26, 2023 at 06:06:26PM +0800, Zhu Wang wrote:
> When building with W=1, the following warning occurs.
> 
> drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c:48:17: warning: ‘anx781x_i2c_addresses’ defined but not used [-Wunused-const-variable=]
>  static const u8 anx781x_i2c_addresses[] = {
>                  ^~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c:40:17: warning: ‘anx7808_i2c_addresses’ defined but not used [-Wunused-const-variable=]
>  static const u8 anx7808_i2c_addresses[] = {
> 
> The definition of above two data variables is included by the
> macro CONFIG_OF, so we also include the data variable
> definitions in the macro CONFIG_OF. And in addition the data
> variable anx78xx_match_table is included in the macro CONFIG_OF,
> so we add CONFIG_OF to the place where it is used.
> 
> Fixes: 5d97408e0d70 ("drm/bridge: move ANA78xx driver to analogix subdirectory")
> 
> Signed-off-by: Zhu Wang <wangzhu9@...wei.com>
> ---
>  drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c b/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
> index 06a3e3243e19..799b33cebdd5 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c
> @@ -37,6 +37,7 @@
>  
>  #define XTAL_CLK		270 /* 27M */
>  
> +#if IS_ENABLED(CONFIG_OF)
>  static const u8 anx7808_i2c_addresses[] = {
>  	[I2C_IDX_TX_P0] = 0x78,
>  	[I2C_IDX_TX_P1] = 0x7a,
> @@ -52,6 +53,7 @@ static const u8 anx781x_i2c_addresses[] = {
>  	[I2C_IDX_RX_P0] = 0x7e,
>  	[I2C_IDX_RX_P1] = 0x80,
>  };
> +#endif

You can mark anx7808_i2c_addresses with __maybe_unused, then the #if
isn't needed.

>  struct anx78xx_platform_data {
>  	struct regulator *dvdd10;
> @@ -1387,7 +1389,9 @@ MODULE_DEVICE_TABLE(of, anx78xx_match_table);
>  static struct i2c_driver anx78xx_driver = {
>  	.driver = {
>  		   .name = "anx7814",
> +#if IS_ENABLED(CONFIG_OF)
>  		   .of_match_table = of_match_ptr(anx78xx_match_table),
> +#endif

If CONFIG_OF is disabled of_match_ptr(something) evaluates to NULL, so
you can drop the #if here.

Having said that the better fix is probably to just do

	.of_match_table = anx78xx_match_table,

as systems using ACPI can benefit from the of_match_table, too.
See b89a9e9890d4 ("gpio: aggregator: Remove CONFIG_OF and of_match_ptr()
protections") for an example.

Best regards
Uwe

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

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