linux-kernel - Re: [PATCH v2] drm/vkms: Fix cpu_to_le16()/le16_to

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Message-ID: <ZpY8mS0UtIPUu88i@louis-chauvet-laptop>
Date: Tue, 16 Jul 2024 11:25:45 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: rodrigosiqueiramelo@...il.com, melissa.srw@...il.com,
	mairacanal@...eup.net, hamohammed.sa@...il.com, daniel@...ll.ch,
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/vkms: Fix cpu_to_le16()/le16_to_cpu() warnings

Le 15/07/24 - 17:16, José Expósito a écrit :
> Building with Sparse enabled prints this warning for cpu_to_le16()
> calls:
> 
>     warning: incorrect type in assignment (different base types)
>         expected unsigned short [usertype]
>         got restricted __le16 [usertype]
> 
> And this warning for le16_to_cpu() calls:
> 
>     warning: cast to restricted __le16
> 
> Declare the target buffer as __le16 to fix both warnings.
> 
> Signed-off-by: José Expósito <jose.exposito89@...il.com>
> 
> ---
> 
> v1 -> v2: https://lore.kernel.org/dri-devel/20240712161656.7480-1-jose.exposito89@gmail.com/T/
> 
>  - Thomas Zimmermann: Declare "pixels" cariable as __le16 instead of
>    multiple casting.
> ---
>  drivers/gpu/drm/vkms/vkms_formats.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
> index 36046b12f296..1ff535222bd4 100644
> --- a/drivers/gpu/drm/vkms/vkms_formats.c
> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> @@ -75,7 +75,7 @@ static void XRGB8888_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixe
>  
>  static void ARGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
>  {
> -	u16 *pixels = (u16 *)src_pixels;
> +	__le16 *pixels = (__force __le16 *)src_pixels;

Hi,

I think you don't need __force for this cast, so you can remove it.

>  	out_pixel->a = le16_to_cpu(pixels[3]);
>  	out_pixel->r = le16_to_cpu(pixels[2]);
> @@ -85,7 +85,7 @@ static void ARGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_
>  
>  static void XRGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
>  {
> -	u16 *pixels = (u16 *)src_pixels;
> +	__le16 *pixels = (__force __le16 *)src_pixels;
>  	out_pixel->a = (u16)0xffff;
>  	out_pixel->r = le16_to_cpu(pixels[2]);
> @@ -95,7 +95,7 @@ static void XRGB16161616_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_
>  
>  static void RGB565_to_argb_u16(u8 *src_pixels, struct pixel_argb_u16 *out_pixel)
>  {
> -	u16 *pixels = (u16 *)src_pixels;
> +	__le16 *pixels = (__force __le16 *)src_pixels;
>  
>  	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
>  	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
> @@ -178,7 +178,7 @@ static void argb_u16_to_XRGB8888(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel
>  
>  static void argb_u16_to_ARGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>  {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	__le16 *pixels = (__force __le16 *)dst_pixels;
>
>  	pixels[3] = cpu_to_le16(in_pixel->a);
>  	pixels[2] = cpu_to_le16(in_pixel->r);
> @@ -188,9 +188,9 @@ static void argb_u16_to_ARGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_p
>  
>  static void argb_u16_to_XRGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>  {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	__le16 *pixels = (__force __le16 *)dst_pixels;
>
> -	pixels[3] = 0xffff;
> +	pixels[3] = (__force __le16)0xffff;

I agree with Thomas Zimmerman, I prefer cpu_to_le16().

With or without those modifications:

Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>

Thanks,
Louis Chauvet

>  	pixels[2] = cpu_to_le16(in_pixel->r);
>  	pixels[1] = cpu_to_le16(in_pixel->g);
>  	pixels[0] = cpu_to_le16(in_pixel->b);
> @@ -198,7 +198,7 @@ static void argb_u16_to_XRGB16161616(u8 *dst_pixels, struct pixel_argb_u16 *in_p
>  
>  static void argb_u16_to_RGB565(u8 *dst_pixels, struct pixel_argb_u16 *in_pixel)
>  {
> -	u16 *pixels = (u16 *)dst_pixels;
> +	__le16 *pixels = (__force __le16 *)dst_pixels;
>  
>  	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
>  	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
> -- 
> 2.45.2
> 

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com