From b527834c8821362da6d01ee15ecab589a43abfcb Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Mon, 2 Jul 2018 23:46:59 +0200
Subject: [PATCH 4/9] drm: Remove unnecessary reset_scan_out_buffer_if_needed()
 call from ply_renderer_head_map()

ply_renderer_head_map() gets only called from map_to_device() which
calls activate() directly afterwards which calls
ply_renderer_head_set_scan_out_buffer(), so there is no need for the
reset_scan_out_buffer_if_needed() call.

Not only is it not needed, but it is actually harmful, there are 2 problems
woth it:

1) Normally the drm plugin gets instantiated by ply-renderer.c with
   rendered->is_active=true, backend->is_active=false. The
   rendered->is_active=true causes the first ply_renderer_activate call
   to be a no-op without calling backend->activate(). So when the first
   map_to_device() calls happen activate() has not been called yet and we've
   not yet claimed master rights, so ply_renderer_head_set_scan_out_buffer()
   calls will always fail, resulting in this in a ply-trace:

   Mapping buffer for 1920x1080 renderer head
   Redrawing 1920x1080 renderer head
   Setting scan out buffer of 1920x1080 head to our buffer
   Couldn't set scan out buffer for head with controller id 41

   This is harmless, but also shows that the reset_scan_out_buffer_if_needed()
   is really not needed.

2. If deactivate_renderer() gets called before the first show-splash then
   rendered->is_active will become false, so renderer_activate() done before
   map_to_device() will now actually call backend->activate() claiming
   drm master rights and setting backend->is_active=true.

   The map_to_device() -> ply_renderer_head_map() call done after this, calls
   ply_renderer_head_redraw() -> flush_head() which under 1. was a no-op
   as it exits directly when backend->is_active=false. But now it actually
   flushes the buffers by calling reset_scan_out_buffer_if_needed(). This
   itself is fine.

   But since reset_scan_out_buffer_if_needed() has already happened in
   ply_renderer_head_redraw() the reset_scan_out_buffer_if_needed() call this
   commit removes would always return false (no reset necessary) causing
   ply_renderer_head_map() to destroy the buffer and return an error.

   This results in the splash briefly showing, followed by the core soon after
   trying another map_to_device(), which again briefly shows the splash, etc.
   With the end result being a badly flickering display.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 src/plugins/renderers/drm/plugin.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/src/plugins/renderers/drm/plugin.c b/src/plugins/renderers/drm/plugin.c
index fb79aa6..1080590 100644
--- a/src/plugins/renderers/drm/plugin.c
+++ b/src/plugins/renderers/drm/plugin.c
@@ -618,8 +618,6 @@ static bool
 ply_renderer_head_map (ply_renderer_backend_t *backend,
                        ply_renderer_head_t    *head)
 {
-        bool scan_out_set;
-
         assert (backend != NULL);
         assert (backend->device_fd >= 0);
         assert (backend != NULL);
@@ -646,13 +644,6 @@ ply_renderer_head_map (ply_renderer_backend_t *backend,
          */
         ply_renderer_head_redraw (backend, head);
 
-        scan_out_set = reset_scan_out_buffer_if_needed (backend, head);
-        if (!scan_out_set && backend->is_active) {
-                destroy_output_buffer (backend, head->scan_out_buffer_id);
-                head->scan_out_buffer_id = 0;
-                return false;
-        }
-
         return true;
 }
 
-- 
2.18.0