Re: [PATCH] tpm: Use named initializers for arrays of i2c_device_data

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, May 18, 2026 at 03:40:35PM +0200, Uwe Kleine-König (The Capable Hub) wrote:
> While being less compact, using named initializers allows to more easily
> see which members of the structs are assigned which value without having
> to lookup the declaration of the struct. And it's also more robust
> against changes to the struct definition.
> 
> The mentioned robustness is relevant for a planned change to struct
> i2c_device_id that replaces .driver_data by an anonymous union.
> 
> While touching all these arrays, unify usage of whitespace in the list
> terminator.
> 
> This patch doesn't modify the compiled arrays, only their representation
> in source form benefits. The former was confirmed with x86 and arm64
> builds.
> 
> Signed-off-by: Uwe Kleine-König (The Capable Hub) <u.kleine-koenig@baylibre.com>
> ---
> Hello,
> 
> the mentioned change to i2c_device_id is the following:
> 
> 	diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
> 	index 23ff24080dfd..aebd3a5e90af 100644
> 	--- a/include/linux/mod_devicetable.h
> 	+++ b/include/linux/mod_devicetable.h
> 	@@ -477,7 +477,11 @@ struct rpmsg_device_id {
> 
> 	 struct i2c_device_id {
> 		char name[I2C_NAME_SIZE];
> 	-	kernel_ulong_t driver_data;	/* Data private to the driver */
> 	+	union {
> 	+		/* Data private to the driver */
> 	+		kernel_ulong_t driver_data;
> 	+		const void *driver_data_ptr;
> 	+	};
> 	 };
> 
> 	 /* pci_epf */
> 
> and this requires that .driver_data is assigned via a named initializer
> for static data. This requirement isn't a bad one because named
> initializers are also much better readable than list initializers.
> 
> The union added to struct i2c_device_id enables further cleanups like:
> 
> 	diff --git a/drivers/regulator/ad5398.c b/drivers/regulator/ad5398.c
> 	index 0123ca8157a8..dfb0b07500a7 100644
> 	--- a/drivers/regulator/ad5398.c
> 	+++ b/drivers/regulator/ad5398.c
> 	@@ -207,8 +207,8 @@ struct ad5398_current_data_format {
> 	 static const struct ad5398_current_data_format df_10_4_120 = {10, 4, 0, 120000};
> 
> 	 static const struct i2c_device_id ad5398_id[] = {
> 	-	{ .name = "ad5398", .driver_data = (kernel_ulong_t)&df_10_4_120 },
> 	-	{ .name = "ad5821", .driver_data = (kernel_ulong_t)&df_10_4_120 },
> 	+	{ .name = "ad5398", .driver_data_ptr = &df_10_4_120 },
> 	+	{ .name = "ad5821", .driver_data_ptr = &df_10_4_120 },
> 	 	{ }
> 	 };
> 	 MODULE_DEVICE_TABLE(i2c, ad5398_id);
> 	@@ -219,8 +219,7 @@ static int ad5398_probe(struct i2c_client *client)
> 	 	struct regulator_init_data *init_data = dev_get_platdata(&client->dev);
> 	 	struct regulator_config config = { };
> 	 	struct ad5398_chip_info *chip;
> 	-	const struct ad5398_current_data_format *df =
> 	-	                (struct ad5398_current_data_format *)id->driver_data;
> 	+	const struct ad5398_current_data_format *df = id->driver_data;
> 
> 	 	chip = devm_kzalloc(&client->dev, sizeof(*chip), GFP_KERNEL);
> 	 	if (!chip)
> 
> that are an improvement for readability (again!) and it keeps some
> properties of the pointers (here: being const) without having to pay
> attention for that. (I didn't find a tpm driver that benefits, so this
> is "only" a regulator driver example.)
> 
> My additional motivation for this effort is CHERI[1]. This is a hardware
> extension that uses 128 bit pointers but unsigned long is still 64 bit.
> So with CHERI you cannot store pointers in unsigned long variables.

I don't understand why any of this should be merged to be honest, and
why I should care about CHERI when reviewing mainline patches.

Clean up can be side-effect but not a purpose.

> 
> Best regards
> Uwe
> 
> [1] https://cheri-alliance.org/discover-cheri/
>     https://lwn.net/Articles/1037974/
> ---
>  drivers/char/tpm/st33zp24/i2c.c     | 4 ++--
>  drivers/char/tpm/tpm_i2c_atmel.c    | 4 ++--
>  drivers/char/tpm/tpm_i2c_infineon.c | 8 ++++----
>  drivers/char/tpm/tpm_i2c_nuvoton.c  | 6 +++---
>  drivers/char/tpm/tpm_tis_i2c.c      | 4 ++--
>  5 files changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/char/tpm/st33zp24/i2c.c b/drivers/char/tpm/st33zp24/i2c.c
> index 81348487c125..74b25af5ce79 100644
> --- a/drivers/char/tpm/st33zp24/i2c.c
> +++ b/drivers/char/tpm/st33zp24/i2c.c
> @@ -133,8 +133,8 @@ static void st33zp24_i2c_remove(struct i2c_client *client)
>  }
>  
>  static const struct i2c_device_id st33zp24_i2c_id[] = {
> -	{ TPM_ST33_I2C },
> -	{}
> +	{ .name = TPM_ST33_I2C },
> +	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, st33zp24_i2c_id);
>  
> diff --git a/drivers/char/tpm/tpm_i2c_atmel.c b/drivers/char/tpm/tpm_i2c_atmel.c
> index 9fd73049821f..6891642a7f51 100644
> --- a/drivers/char/tpm/tpm_i2c_atmel.c
> +++ b/drivers/char/tpm/tpm_i2c_atmel.c
> @@ -199,8 +199,8 @@ static void i2c_atmel_remove(struct i2c_client *client)
>  }
>  
>  static const struct i2c_device_id i2c_atmel_id[] = {
> -	{ I2C_DRIVER_NAME },
> -	{}
> +	{ .name = I2C_DRIVER_NAME },
> +	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, i2c_atmel_id);
>  
> diff --git a/drivers/char/tpm/tpm_i2c_infineon.c b/drivers/char/tpm/tpm_i2c_infineon.c
> index 8b7d32de0b2e..29cf2f998405 100644
> --- a/drivers/char/tpm/tpm_i2c_infineon.c
> +++ b/drivers/char/tpm/tpm_i2c_infineon.c
> @@ -664,10 +664,10 @@ static int tpm_tis_i2c_init(struct device *dev)
>  }
>  
>  static const struct i2c_device_id tpm_tis_i2c_table[] = {
> -	{"tpm_i2c_infineon"},
> -	{"slb9635tt"},
> -	{"slb9645tt"},
> -	{},
> +	{ .name = "tpm_i2c_infineon" },
> +	{ .name = "slb9635tt" },
> +	{ .name = "slb9645tt" },
> +	{ }
>  };
>  
>  MODULE_DEVICE_TABLE(i2c, tpm_tis_i2c_table);
> diff --git a/drivers/char/tpm/tpm_i2c_nuvoton.c b/drivers/char/tpm/tpm_i2c_nuvoton.c
> index d44903b29929..71c59eeaccab 100644
> --- a/drivers/char/tpm/tpm_i2c_nuvoton.c
> +++ b/drivers/char/tpm/tpm_i2c_nuvoton.c
> @@ -624,9 +624,9 @@ static void i2c_nuvoton_remove(struct i2c_client *client)
>  }
>  
>  static const struct i2c_device_id i2c_nuvoton_id[] = {
> -	{"tpm_i2c_nuvoton"},
> -	{"tpm2_i2c_nuvoton", .driver_data = I2C_IS_TPM2},
> -	{}
> +	{ .name = "tpm_i2c_nuvoton" },
> +	{ .name = "tpm2_i2c_nuvoton", .driver_data = I2C_IS_TPM2},
> +	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, i2c_nuvoton_id);
>  
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> index 6cd07dd34507..21d66bfba6a8 100644
> --- a/drivers/char/tpm/tpm_tis_i2c.c
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -375,8 +375,8 @@ static void tpm_tis_i2c_remove(struct i2c_client *client)
>  }
>  
>  static const struct i2c_device_id tpm_tis_i2c_id[] = {
> -	{ "tpm_tis_i2c" },
> -	{}
> +	{ .name = "tpm_tis_i2c" },
> +	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, tpm_tis_i2c_id);
>  
> -- 
> 2.47.3
> 

BR, Jarkko