Re: [PATCH] staging: media: tegra-video: use BIT() macro instead of shift

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Hello A.T. Jefferies,

On Wed, 23 Jul 2025 23:17:57 +0000
"A.T. Jefferies" <alextjefferies@gmail.com> wrote:

> Replace two instances of (1 << X) with BIT(X) in tegra20.c to follow
> kernel coding style guidelines and improve clarity. The BIT() macro
> also ensures proper type handling for larger shifts.
> 
> Signed-off-by: A.T. Jefferies <alextjefferies@gmail.com>
> ---
>  drivers/staging/media/tegra-video/tegra20.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/tegra-video/tegra20.c b/drivers/staging/media/tegra-video/tegra20.c
> index 7b8f8f810b35..1473f1b1f203 100644
> --- a/drivers/staging/media/tegra-video/tegra20.c
> +++ b/drivers/staging/media/tegra-video/tegra20.c
> @@ -42,7 +42,7 @@
>  #define       VI_INPUT_BT656				BIT(25)
>  #define       VI_INPUT_YUV_INPUT_FORMAT_SFT		8  /* bits [9:8] */
>  #define       VI_INPUT_YUV_INPUT_FORMAT_UYVY		(0 << VI_INPUT_YUV_INPUT_FORMAT_SFT)
> -#define       VI_INPUT_YUV_INPUT_FORMAT_VYUY		(1 << VI_INPUT_YUV_INPUT_FORMAT_SFT)
> +#define       VI_INPUT_YUV_INPUT_FORMAT_VYUY		BIT(VI_INPUT_YUV_INPUT_FORMAT_SFT)
>  #define       VI_INPUT_YUV_INPUT_FORMAT_YUYV		(2 << VI_INPUT_YUV_INPUT_FORMAT_SFT)
>  #define       VI_INPUT_YUV_INPUT_FORMAT_YVYU		(3 << VI_INPUT_YUV_INPUT_FORMAT_SFT)

Thanks for your patch. However I'm afraid I don't think this is a good
idea. 1 is just one out of 4 possible values out of 4 possible values
for a multi-bit register field. All the 4 should use the same style.

BIT() is perfect for single-bit register fields. It's not for multi-bit
fields.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com