linux-kernel - Re: [PATCH] drm/fb_helper: Use min_t() to handle size

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Date:   Tue, 10 Nov 2020 10:17:44 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/fb_helper: Use min_t() to handle size_t and unsigned
 long

Hi

Am 10.11.20 um 10:01 schrieb Geert Uytterhoeven:
> On arm32:
> 
>     drivers/gpu/drm/drm_fb_helper.c: In function ‘fb_read_screen_base’:
>     include/linux/minmax.h:18:28: warning: comparison of distinct pointer types lacks a cast
>     ...
>     drivers/gpu/drm/drm_fb_helper.c:2041:22: note: in expansion of macro ‘min’
>      2041 |  size_t alloc_size = min(count, PAGE_SIZE);
> 	  |                      ^~~
>     drivers/gpu/drm/drm_fb_helper.c: In function ‘fb_write_screen_base’:
>     include/linux/minmax.h:18:28: warning: comparison of distinct pointer types lacks a cast
>     ...
>     drivers/gpu/drm/drm_fb_helper.c:2115:22: note: in expansion of macro ‘min’
>      2115 |  size_t alloc_size = min(count, PAGE_SIZE);
> 	  |                      ^~~
> 
> Indeed, on 32-bit size_t is "unsigned int", not "unsigned long".
> 
> Fixes: 222ec45f4c69dfa8 ("drm/fb_helper: Support framebuffers in I/O memory")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

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

Thanks a lot. I'll add the patch to drm-misc-next.

> ---
> Interestingly, the commit log claims v7 changed:
> 
>     use min_t(size_t,) (kernel test robot)

It got fixed in the functions' inner loops, but I missed the other
instances.

Best regards
Thomas

> ---
>  drivers/gpu/drm/drm_fb_helper.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 01ba1da285116373..25edf670867c6f79 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2038,7 +2038,7 @@ static ssize_t fb_read_screen_base(struct fb_info *info, char __user *buf, size_
>  				   loff_t pos)
>  {
>  	const char __iomem *src = info->screen_base + pos;
> -	size_t alloc_size = min(count, PAGE_SIZE);
> +	size_t alloc_size = min_t(size_t, count, PAGE_SIZE);
>  	ssize_t ret = 0;
>  	int err = 0;
>  	char *tmp;
> @@ -2112,7 +2112,7 @@ static ssize_t fb_write_screen_base(struct fb_info *info, const char __user *buf
>  				    loff_t pos)
>  {
>  	char __iomem *dst = info->screen_base + pos;
> -	size_t alloc_size = min(count, PAGE_SIZE);
> +	size_t alloc_size = min_t(size_t, count, PAGE_SIZE);
>  	ssize_t ret = 0;
>  	int err = 0;
>  	u8 *tmp;
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer