panfrost: fix off-by-one when exporting format modifiers

`count` should not be incremented before the check, because it causes
the modifiers array to be filled starting from position 1 instead of 0.

This bug causes one less format modifier to be available than would
otherwise be expected, which could then lead to a dmabuf query failing
in situations where a supported modifier wouldn't be advertised.

It also causes garbage data to be advertised as a modifier in position 0
of the array, although this is not very likely to cause issues.

Fixes: 2a1217513 ("panfrost: Implement panfrost_query_dmabuf_modifiers")
Cc: mesa-stable
Signed-off-by: Italo Nicola <italonicola@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20879>

diff --git a/src/gallium/drivers/panfrost/pan_screen.c b/src/gallium/drivers/panfrost/pan_screen.c
index e6ecc69..9235023 100644 (file)
--- a/src/gallium/drivers/panfrost/pan_screen.c
+++ b/src/gallium/drivers/panfrost/pan_screen.c
@@ -629,14 +629,13 @@ panfrost_walk_dmabuf_modifiers(struct pipe_screen *screen,
           test_modifier != pan_best_modifiers[i])
          continue;
 
-      count++;
-
       if (max > (int)count) {
          modifiers[count] = pan_best_modifiers[i];
 
          if (external_only)
             external_only[count] = false;
       }
+      count++;
    }
 
    *out_count = count;