linux-kernel - Re: [PATCH] drm/pl111: Use 64-bit arithmetic instead of 32-bit

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Message-ID: <aacd8a63-988a-6188-22cd-40d5e3c241ee@embeddedor.com>
Date:   Wed, 4 Jul 2018 09:11:27 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Eric Anholt <eric@...olt.net>, David Airlie <airlied@...ux.ie>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/pl111: Use 64-bit arithmetic instead of 32-bit

Hi,

Please, ignore this. I should have used ULL instead of UL.

I'll send v2 shortly.

Thanks
--
Gustavo

On 07/03/2018 06:51 PM, Gustavo A. R. Silva wrote:
> Add suffix UL to constant 1000 in order to give the compiler complete
> information about the proper arithmetic to use.
> 
> Notice that such constant is used in a context that expects an
> expression of type u64 (64 bits, unsigned) and the following
> expression is currently being evaluated using 32-bit arithmetic:
> 
> mode->clock * 1000
> 
> Addresses-Coverity-ID: 1466139 ("Unintentional integer overflow")
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/gpu/drm/pl111/pl111_display.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
> index a432eb7..61d51b4 100644
> --- a/drivers/gpu/drm/pl111/pl111_display.c
> +++ b/drivers/gpu/drm/pl111/pl111_display.c
> @@ -63,7 +63,7 @@ pl111_mode_valid(struct drm_crtc *crtc,
>  	 * We use the pixelclock to also account for interlaced modes, the
>  	 * resulting bandwidth is in bytes per second.
>  	 */
> -	bw = mode->clock * 1000; /* In Hz */
> +	bw = mode->clock * 1000UL; /* In Hz */
>  	bw = bw * mode->hdisplay * mode->vdisplay * cpp;
>  	bw = div_u64(bw, mode->htotal * mode->vtotal);
>  
>