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

[Liu Ying]

On Mon, May 18, 2026 at 12:04:01PM +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 and drop trailing commas there.
> 
> 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@xxxxxxxxxxxx>
> ---
> 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..84272ba65d08 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_ptr;
> 	 
> 		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 nice driver below drivers/gpu 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 was unsure if I should split the patch. I guess doing all of
> drivers/gpu/drm/bridge together is fine, please tell if I should split
> off drivers/gpu/drm/nouveau/ and/or drivers/gpu/drm/sitronix/.
> 
> Best regards
> Uwe
> 
> [1] https://cheri-alliance.org/discover-cheri/
>     https://lwn.net/Articles/1037974/
> 
>  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c           | 10 +++++-----
>  drivers/gpu/drm/bridge/analogix/analogix-anx6345.c     |  2 +-
>  drivers/gpu/drm/bridge/analogix/anx7625.c              |  4 ++--
>  drivers/gpu/drm/bridge/chipone-icn6211.c               |  4 ++--
>  drivers/gpu/drm/bridge/chrontel-ch7033.c               |  2 +-
>  drivers/gpu/drm/bridge/ite-it6263.c                    |  2 +-

Reviewed-by: Liu Ying <victor.liu@xxxxxxx> # ite-it6263.c

-- 
Regards,
Liu Ying