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Panels often support backlight as specified in a device tree.
Update the drm_panel infrastructure to support this to
simplify the drivers.
With this the panel driver just needs to add the following to the
probe() function:
err = drm_panel_of_backlight(panel);
if (err)
return err;
Then drm_panel will handle all the rest.
There is one caveat with the backlight support.
If drm_panel_(enable|disable) are called multiple times
in a row then backlight_(enable|disable) will be called multiple times.
The above will happen when a panel drivers unconditionally
calls drm_panel_disable() in their shutdown() function,
whan the panel is already disabled and then shutdown() is called.
Reading the backlight code it seems safe to call
the backlight_(enable|disable) several times.
v3:
- Improve comments, fix grammar (Laurent)
- Do not fail in drm_panel_of_backlight() if no DT support (Laurent)
- Log if backlight_(enable|disable) fails (Laurent)
- Improve drm_panel_of_backlight() docs
- Updated changelog with backlight analysis (triggered by Laurent)
v2:
- Drop test of CONFIG_DRM_PANEL in header-file (Laurent)
- do not enable backlight if ->enable() returns an error
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191207140353.23967-3-sam@ravnborg.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.