Many panel data sheets, additionally to typical values, list allowed
ranges for timings such as hsync/vsync lengths, porches, and the pixel
clock rate. These can be stored in a struct display_timing, to be used
by an encoder mode_fixup callback to clamp user provided timing values
or to validate workarounds for clock source limitations.

This patch adds a new drm_panel_funcs callback that returns the panel's
available display_timing entries.
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: NThierry Reding <treding@nvidia.com>

Add a convenience wrapper for the struct drm_panel_funcs' .get_modes()
function so that not every driver needs to check that the panel driver
implements the function before calling it.
Signed-off-by: NAjay Kumar <ajaykumar.rs@samsung.com>
[treding: extract from larger patch, commit message]
Signed-off-by: NThierry Reding <treding@nvidia.com>

Panels often require an initialization sequence that consists of three
steps: a) powering up the panel, b) starting transmission of video data
and c) enabling the panel (e.g. turn on backlight). This is usually
necessary to avoid visual glitches at the beginning of video data
transmission.

Similarly, the shutdown sequence is typically done in three steps as
well: a) disable the panel (e.g. turn off backlight), b) cease video
data transmission and c) power down the panel.

Currently drivers can only implement .enable() and .disable() functions,
which is not enough to implement the above sequences. This commit adds a
second pair of functions, .prepare() and .unprepare() to allow more
fine-grained control over when the above steps are performed.
Signed-off-by: NAjay Kumar <ajaykumar.rs@samsung.com>
[treding: rewrite changelog, add kerneldoc]
Signed-off-by: NThierry Reding <treding@nvidia.com>

Add a very simple framework to register and lookup panels. Panel drivers
can initialize a DRM panel and register it with the framework, allowing
them to be retrieved and used by display drivers. Currently only support
for DPMS and obtaining panel modes is provided. However it should be
sufficient to enable a large number of panels. The framework should also
be easily extensible to support more sophisticated kinds of panels such
as DSI.

The framework hasn't been tied into the DRM core, even though it should
be easily possible to do so if that's what we want. In the current
implementation, display drivers can simple make use of it to retrieve a
panel, obtain its modes and control its DPMS mode.

Note that this is currently only tested on systems that boot from a
device tree. No glue code has been written yet for systems that use
platform data, but it should be easy to add.
Signed-off-by: NThierry Reding <treding@nvidia.com>