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drm/panel: Update TODO list item for cleaning up prepared/enabled tracking

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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@linaro.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240604172305.v3.23.I104cdece7324b0c365e552a17f9883414ffaea01@changeid
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240604172305.v3.23.I104cdece7324b0c365e552a17f9883414ffaea01@changeid
This commit is contained in:
Douglas Anderson 2024-06-04 17:23:09 -07:00 committed by Neil Armstrong
parent 78f15847bd
commit 8e11b23c96
1 changed files with 23 additions and 18 deletions
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41
Documentation/gpu/todo.rst
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@ -469,30 +469,35 @@ Contact: Thomas Zimmermann <tzimmermann@suse.de>
Level: Starter
Clean up checks for already prepared/enabled in panels
------------------------------------------------------
Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp
-------------------------------------------------------------------------
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::
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.
git grep 'if.*>prepared' -- drivers/gpu/drm/panel
git grep 'if.*>enabled' -- drivers/gpu/drm/panel
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.
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.
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@chromium.org>
Level: Starter/Intermediate
Level: Intermediate
Transition away from using mipi_dsi_*_write_seq()
-------------------------------------------------