present: Document the TearFree flip reasons in PresentFlipReason

Adding new flip reasons after the TearFree ones would break the assumption
that `reason >= PRESENT_FLIP_REASON_DRIVER_TEARFREE` implies either of the
TearFree reasons. Document this in the PresentFlipReason enum in order to
save someone a very bad headache in the future.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Reviewed-by: Martin Roukala <martin.roukala@mupuf.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/present/present.h b/present/present.h
index 1d7b0ce42..a3f34a929 100644
--- a/present/present.h
+++ b/present/present.h
@@ -30,6 +30,12 @@
 typedef enum {
     PRESENT_FLIP_REASON_UNKNOWN,
     PRESENT_FLIP_REASON_BUFFER_FORMAT,
+
+    /* Don't add new flip reasons after the TearFree ones, since it's expected
+     * that the TearFree reasons are the highest ones in order to allow doing
+     * `reason >= PRESENT_FLIP_REASON_DRIVER_TEARFREE` to check if a reason is
+     * PRESENT_FLIP_REASON_DRIVER_TEARFREE{_FLIPPING}.
+     */
     PRESENT_FLIP_REASON_DRIVER_TEARFREE,
     PRESENT_FLIP_REASON_DRIVER_TEARFREE_FLIPPING
 } PresentFlipReason;