linux-kernel - [PATCH v3 23/24] drm/panel: Update TODO list item for cleaning up prepared/enabled tracking

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Message-ID: <20240604172305.v3.23.I104cdece7324b0c365e552a17f9883414ffaea01@changeid>
Date: Tue,  4 Jun 2024 17:23:09 -0700
From: Douglas Anderson <dianders@...omium.org>
To: dri-devel@...ts.freedesktop.org,
	Maxime Ripard <mripard@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>,
	Chris Morgan <macromorgan@...mail.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Yuran Pereira <yuran.pereira@...mail.com>,
	Douglas Anderson <dianders@...omium.org>,
	Daniel Vetter <daniel@...ll.ch>,
	David Airlie <airlied@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 23/24] drm/panel: Update TODO list item for cleaning up prepared/enabled tracking

Now that most panels have been updated not to track/double-check their
prepared/enabled state update the TODO with next steps.

Acked-by: Linus Walleij <linus.walleij@...aro.org>
Acked-by: Maxime Ripard <mripard@...nel.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

(no changes since v1)

 Documentation/gpu/todo.rst | 47 +++++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 21 deletions(-)

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 2734b8a34541..2ea6ffc9b22b 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -469,30 +469,35 @@ Contact: Thomas Zimmermann <tzimmermann@...e.de>
 
 Level: Starter
 
-Clean up checks for already prepared/enabled in panels
-------------------------------------------------------
-
-In a whole pile of panel drivers, we have code to make the
-prepare/unprepare/enable/disable callbacks behave as no-ops if they've already
-been called. To get some idea of the duplicated code, try::
-
-  git grep 'if.*>prepared' -- drivers/gpu/drm/panel
-  git grep 'if.*>enabled' -- drivers/gpu/drm/panel
-
-In the patch ("drm/panel: Check for already prepared/enabled in drm_panel")
-we've moved this check to the core. Now we can most definitely remove the
-check from the individual panels and save a pile of code.
-
-In adition to removing the check from the individual panels, it is believed
-that even the core shouldn't need this check and that should be considered
-an error if other code ever relies on this check. The check in the core
-currently prints a warning whenever something is relying on this check with
-dev_warn(). After a little while, we likely want to promote this to a
-WARN(1) to help encourage folks not to rely on this behavior.
+Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp
+-------------------------------------------------------------------------
+
+As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in
+drm_panel"), we have a check in the drm_panel core to make sure nobody
+double-calls prepare/enable/disable/unprepare. Eventually that should probably
+be turned into a WARN_ON() or somehow made louder, but right now we actually
+expect it to trigger and so we don't want it to be too loud.
+
+Specifically, that warning will trigger for panel-edp and panel-simple at
+shutdown time because those panels hardcode a call to drm_panel_disable()
+and drm_panel_unprepare() at shutdown and remove time that they call regardless
+of panel state. On systems with a properly coded DRM modeset driver that
+calls drm_atomic_helper_shutdown() this is pretty much guaranteed to cause
+the warning to fire.
+
+Unfortunately we can't safely remove the calls in panel-edp and panel-simple
+until we're sure that all DRM modeset drivers that are used with those panels
+properly call drm_atomic_helper_shutdown(). This TODO item is to validate
+that all DRM modeset drivers used with panel-edp and panel-simple properly
+call drm_atomic_helper_shutdown() and then remove the calls to
+disable/unprepare from those panels. Alternatively, this TODO item could be
+removed by convincing stakeholders that those calls are fine and downgrading
+the error message in drm_panel_disable() / drm_panel_unprepare() to a
+debug-level message.
 
 Contact: Douglas Anderson <dianders@...omium.org>
 
-Level: Starter/Intermediate
+Level: Intermediate
 
 Transition away from using mipi_dsi_*_write_seq()
 -------------------------------------------------
-- 
2.45.1.288.g0e0cd299f1-goog