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

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Message-ID: <aa140df8-efc0-49f0-9c65-64bee7cc437e@suse.de>
Date: Mon, 15 Jul 2024 17:38:03 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: José Expósito <jose.exposito89@...il.com>,
 rodrigosiqueiramelo@...il.com
Cc: melissa.srw@...il.com, mairacanal@...eup.net, hamohammed.sa@...il.com,
 daniel@...ll.ch, maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 airlied@...il.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, louis.chauvet@...tlin.com
Subject: Re: [PATCH v2] drm/vkms: Fix cpu_to_le16()/le16_to_cpu() warnings

Hi

Am 15.07.24 um 17:16 schrieb José Expósito:
> 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;
>   
>   	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'd use cpu_to_le16() even on the constant. It makes it clear what is 
happening, makes __le16 opaque, and avoids the ugly cast.

In any case

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

Best regards
Thomas

>   	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));

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)