drm/edid: Clarify validate_displayid()

Throw out the magic '5' from validate_displayid() and replace with
the actual thing we mean sizeof(header)+checksum. Also rewrite the
checksum loop to be less hard to parse for mere mortals.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200313162054.16009-9-ville.syrjala@linux.intel.com
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index d86062d..4cc03bf 100644 (file)
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5097,7 +5097,7 @@ u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edi
 
 static int validate_displayid(u8 *displayid, int length, int idx)
 {
-       int i;
+       int i, dispid_length;
        u8 csum = 0;
        struct displayid_hdr *base;
 
@@ -5106,15 +5106,18 @@ static int validate_displayid(u8 *displayid, int length, int idx)
        DRM_DEBUG_KMS("base revision 0x%x, length %d, %d %d\n",
                      base->rev, base->bytes, base->prod_id, base->ext_count);
 
-       if (base->bytes + 5 > length - idx)
+       /* +1 for DispID checksum */
+       dispid_length = sizeof(*base) + base->bytes + 1;
+       if (dispid_length > length - idx)
                return -EINVAL;
-       for (i = idx; i <= base->bytes + 5; i++) {
-               csum += displayid[i];
-       }
+
+       for (i = 0; i < dispid_length; i++)
+               csum += displayid[idx + i];
        if (csum) {
                DRM_NOTE("DisplayID checksum invalid, remainder is %d\n", csum);
                return -EINVAL;
        }
+
        return 0;
 }