[patch] drm: radeon: fix sign bug

[patch] drm: radeon: fix sign bug

[Dan Carpenter]

The "error" variable is unsigned so it's never less than zero.  I
changed it to check if (freq < current_freq) directly.

"best_error" is also unsigned so "best_error - 100" could be a large
number instead of a negative.  Since "error" is unsigned it is never
less than a negative and so the cases where "best_error" is less than or
equal to 100 are false.

Signed-off-by: Dan Carpenter <error27@gmail.com>

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 8154cdf..a68728d 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -558,15 +558,17 @@ static void radeon_compute_pll_legacy(struct radeon_pll *pll,
 					current_freq = radeon_div(tmp, ref_div * post_div);
 
 					if (pll->flags & RADEON_PLL_PREFER_CLOSEST_LOWER) {
-						error = freq - current_freq;
-						error = error < 0 ? 0xffffffff : error;
+						if (freq < current_freq)
+							error = 0xffffffff;
+						else
+							error = freq - current_freq;
 					} else
 						error = abs(current_freq - freq);
 					vco_diff = abs(vco - best_vco);
 
 					if ((best_vco = 0 && error < best_error) ||
 					    (best_vco != 0 &&
-					     (error < best_error - 100 ||
+					     ((best_error > 100 && error < best_error - 100) ||
 					      (abs(error - best_error) < 100 && vco_diff < best_vco_diff)))) {
 						best_post_div = post_div;
 						best_ref_div = ref_div;

Re: [patch] drm: radeon: fix sign bug

[Alex Deucher]

On Sat, Jul 17, 2010 at 6:28 AM, Dan Carpenter <error27@gmail.com> wrote:
> The "error" variable is unsigned so it's never less than zero.  I
> changed it to check if (freq < current_freq) directly.
>
> "best_error" is also unsigned so "best_error - 100" could be a large
> number instead of a negative.  Since "error" is unsigned it is never
> less than a negative and so the cases where "best_error" is less than or
> equal to 100 are false.
>
> Signed-off-by: Dan Carpenter <error27@gmail.com>
>

This looks good Dan.  Dave, please apply,

Reviewed-by: Alex Deucher <alexdeucher@gmail.com>

> diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
> index 8154cdf..a68728d 100644
> --- a/drivers/gpu/drm/radeon/radeon_display.c
> +++ b/drivers/gpu/drm/radeon/radeon_display.c
> @@ -558,15 +558,17 @@ static void radeon_compute_pll_legacy(struct radeon_pll *pll,
>                                        current_freq = radeon_div(tmp, ref_div * post_div);
>
>                                        if (pll->flags & RADEON_PLL_PREFER_CLOSEST_LOWER) {
> -                                               error = freq - current_freq;
> -                                               error = error < 0 ? 0xffffffff : error;
> +                                               if (freq < current_freq)
> +                                                       error = 0xffffffff;
> +                                               else
> +                                                       error = freq - current_freq;
>                                        } else
>                                                error = abs(current_freq - freq);
>                                        vco_diff = abs(vco - best_vco);
>
>                                        if ((best_vco = 0 && error < best_error) ||
>                                            (best_vco != 0 &&
> -                                            (error < best_error - 100 ||
> +                                            ((best_error > 100 && error < best_error - 100) ||
>                                              (abs(error - best_error) < 100 && vco_diff < best_vco_diff)))) {
>                                                best_post_div = post_div;
>                                                best_ref_div = ref_div;
>
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