Features such as dithering and pixel data edge configuration currently
rely on the panel registered with the TCON driver. However, bridges are
also supported in addition to panels for RGB setup.

Instead of retrieving the connector from the panel, get it from the
encoder with the dedicated helper.

Even in the case of bridges, the connector is registered with the
encoder from our driver and is accessible when iterating connectors.
Signed-off-by: NPaul Kocialkowski <contact@paulk.fr>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181107181843.27628-3-contact@paulk.fr

Passing the encoder to the TCON RGB setup functions allows accessing the
connector from the encoder directly instead of relying on the panel.
Signed-off-by: NPaul Kocialkowski <contact@paulk.fr>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181107181843.27628-2-contact@paulk.fr

If tcon->panel pointer is NULL, trying to dereference from it
(i.e. tcon->panel->connector) will cause a null pointer dereference.

Add tcon->panel null pointer check before calling
sun4i_tcon0_mode_set_dithering().
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Fixes: f11adcec ("drm/sun4i: tcon: Add dithering support for
                      RGB565/RGB666 LCD panels")
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005215951.99003-2-giulio.benetti@micronovasrl.com

Since tcon->panel is a pointer returned by of_drm_find_panel() need to
check if it is not NULL, hence a valid pointer.
IS_ERR() instead checks return error values, not NULL pointers.

Substitute "if (!IS_ERR(tcon->panel))" with "if (tcon->panel)".
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005215951.99003-1-giulio.benetti@micronovasrl.com

Having DRM_SUN4I built-in but DRM_SUN8I_MIXER as a loadable module results in
a link error, as we try to access a symbol from the sun8i_tcon_top.ko module:

ERROR: "sun8i_tcon_top_de_config" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!
ERROR: "sun8i_tcon_top_set_hdmi_src" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!
ERROR: "sun8i_tcon_top_of_table" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!

This solves the problem by adding a silent symbol for the tcon_top module,
building it as a separate module in exactly the cases that we need it,
but in a way that it is reachable by the other modules.

Fixes: cf77d79b ("drm/sun4i: tcon: Add another way for matching mixers with tcon")
Fixes: 0305189a ("drm/sun4i: tcon: Add support for R40 TCON")
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: NJon Hunter <jonathanh@nvidia.com>
Tested-by: NMatt Hart <matthew.hart@linaro.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180911113325.11024-1-maxime.ripard@bootlin.com

The hardware supports dithering on TCON channel 0 which is used for LCD
panels.

Dithering is a method of approximating a color from a mixture of other
colors when the required color isn't available. It reduces color
banding artifacts that can be observed when displaying gradients
(e.g. grayscale gradients). This may occur when the image that needs
to be displayed is 24-bit but the LCD panel is a lower bit depth and
does not perform dithering on its own.
Signed-off-by: NJonathan Liu <net147@gmail.com>
[wens@csie.org: check display_info.bpc first; handle LVDS and MIPI DSI]
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907041948.19913-4-wens@csie.org

sun4i_tcon0_mode_set_cpu() currently accepts struct mipi_dsi_device *
as its second parameter. This is derived from drm_encoder.

The DSI encoder is tied to the CPU interface mode of the TCON as a
special case. In theory, if hardware were available, we could also
support normal CPU interface modes. It is better to pass the generic
encoder instead of the specialized mipi_dsi_device, and handle the
differences inside the function.

Passing the encoder would also enable the function to pass it, or any
other data structures related to it, to other functions expecting it.
One such example would be dithering support that will be added in a
later patch, which looks at properties tied to the connector to
determine whether dithering should be enabled or not.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907041948.19913-2-wens@csie.org

R40 TV TCON is basically the same as on A83T. However, it needs special
handling, because it has to set up TCON TOP muxes at runtime.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710203511.18454-14-jernej.skrabec@siol.net

Till now, new way of matching engines with TCONs was reading their
respective ids and match them by those ids. However, with introduction
of TCON TOP, that might not be so straightforward anymore.
- there might be more TCONs that engines (mixers)
- TCON ids might have non-consecutive ids

Workaround that by matching mixer id with TCON index from TCON list.

For example, R40 has 2 mixers and 4 TCONs. Board designer can choose
2 outputs, which are connected to any of those 4 TCONs. As long as there
are only 2 TCONs enabled in DT, using index in list as alternative id,
will allow to match them with mixer 0 and 1.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710203511.18454-13-jernej.skrabec@siol.net

Handle both positive and negative dclk polarity,
according to bus_flags, taking care of this:

On A20 and similar SoCs, the only way to achieve Positive Edge
(Rising Edge), is setting dclk clock phase to 2/3(240°).
By default TCON works in Negative Edge(Falling Edge), this is why phase
is set to 0 in that case.
Unfortunately there's no way to logically invert dclk through IO_POL
register.
The only acceptable way to work, triple checked with scope,
is using clock phase set to 0° for Negative Edge and set to 240° for
Positive Edge.
On A33 and similar SoCs there would be a 90° phase option, but it divides
also dclk by 2.
This patch is a way to avoid quirks all around TCON and DOTCLOCK drivers
for using A33 90° phase divided by 2 and consequently increase code
complexity.

Check if panel is used. TCON can also handle VGA DAC, then panel could
be empty.
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180718142357.120998-1-giulio.benetti@micronovasrl.com

Function sun4i_tcon_find_engine_traverse() doesn't release node if it
needs to traverse of graph deeper than 1 level.

Fix this by calling of_node_put().

Fixes: 49836b11 ("drm/sun4i: tcon: Generalize engine search algorithm")
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710203511.18454-6-jernej.skrabec@siol.net

TV TCONs are always connected to TV or HDMI encoder, so it doesn't make
sense to check if panel or bridge is connected to them.

Check if TCON has channel 0 and only then check for connected panel or
bridges.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-13-jernej.skrabec@siol.net

LVDS and RGB interfaces are always connected to TCONs which have channel
0. It doesn't make sense to try to init them on TV TCONs.

Add a check if TCON has channel 0 before trying to init LVDS or RGB
interface.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-12-jernej.skrabec@siol.net

Current "old" method to find engine worked pretty well for DE2. However,
it doesn't work when TCON TOP is between  mixer (engine) and TCON. TCON
TOP has multiple input ports, but current engine search algorithm
expects only one.

This can be fixed by first looking for output port id and selecting
matching input by subtracting 1 for the next round. This work even if
there is only one input and output.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-11-jernej.skrabec@siol.net

This reverts commit 2c17a436.

The offending commit triggers a run-time fault when accessing the panel
element of the sun4i_tcon structure when no such panel is attached.

It was apparently assumed in said commit that a panel is always used with
the TCON. Although it is often the case, this is not always true.
For instance a bridge might be used instead of a panel.

This issue was discovered using an A13-OLinuXino, that uses the TCON
in RGB mode for a simple DAC-based VGA bridge.

Cc: stable@vger.kernel.org
Signed-off-by: NPaul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180613081647.31183-1-paul.kocialkowski@bootlin.com

The DSI controller needs a particular interface (CPU aka 8080) with some
modifications from the TCON in order to run.

Make sure the TCON is able to provide it when we are using the DSI output.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/129f5928113d2ca865bf5269047c2e4ba6fed5e6.1522835818.git-series.maxime.ripard@bootlin.com

The "CPU" (or Intel 8080) interface uses a different interrupt called
TRI_FINISH (most likely TRI being for trigger) to notify the end of frames,
and hence the VBLANK period.

And that interrupt to the possible VBLANK interrupts source.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/de6d6ad8959da77ea3a974a31a4c0c8391178748.1522835818.git-series.maxime.ripard@bootlin.com

The Allwinner A80 SoC has 2 documented TCONs. The display pipeline
diagram from the user manual shows a third TCON, but it's missing
an interrupt line, and its registers are not explained either.
It's also not used in Allwinner's vendor BSP.

The first TCON only has channel 0, for LCD panel output. The TCON
hardware setup is peculiar in that the eDP reset must also be
deasserted to allow access to the TCON. How the eDP module is wired
in the SoC itself is never explained.

The second TCON only has channel 1, and its output is connected to
the HDMI encoder block.

This patch adds a "needs_edp_reset" field to the tcon quirks structure,
and adds quirks and compatible strings for the 2 documented TCONs.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180315114136.24747-4-wens@csie.org

Handle both positive and negative dclk polarity,
according to bus_flags, taking care of this:

On A20 and similar SoCs, the only way to achieve Positive Edge
(Rising Edge), is setting dclk clock phase to 2/3(240°).
By default TCON works in Negative Edge(Falling Edge), this is why phase
is set to 0 in that case.
Unfortunately there's no way to logically invert dclk through IO_POL
register.
The only acceptable way to work, triple checked with scope,
is using clock phase set to 0° for Negative Edge and set to 240° for
Positive Edge.
On A33 and similar SoCs there would be a 90° phase option, but it divides
also dclk by 2.
This patch is a way to avoid quirks all around TCON and DOTCLOCK drivers
for using A33 90° phase divided by 2 and consequently increase code
complexity.
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1520963677-124239-1-git-send-email-giulio.benetti@micronovasrl.com

Currently the exclusivity is enabled when the rate is set by
the mode setting functions. These functions are called by
mode_set_nofb callback of drm_crc_helper. Then exclusivity
is disabled when tcon is disabled by atomic_disable
callback.

What happens is that mode_set_nofb can be called once when
mode changes, and afterwards the system can call atomic_enable
and atomic_disable multiple times without further calls to
mode_set_nofb.

This happens:

mode_set_nofb   - clk exclusivity is enabled
atomic_enable
atomic_disable  - clk exclusivity is disabled
atomic_enable
atomic_disable  - clk exclusivity is already disabled, leading to WARN
                  in clk_rate_exclusive_put

Solution is to enable exclusivity in sun4i_tcon_channel_set_status.
Signed-off-by: NOndrej Jirman <megous@megous.com>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180310110511.14697-1-megous@megous.com

The current logic to deal with old DT missing the LVDS properties doesn't
take into account whether the LVDS output is supported in the first place,
resulting in spurious error messages on SoCs where it doesn't even matter.

Introduce a new TCON flag to list if LVDS is supported at all to prevent
this from happening.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180221125703.4595-1-maxime.ripard@bootlin.com

Currently exclusive TCON clock lock is never released, which, for
example, prevents changing resolution on HDMI.

In order to fix that, release clock when disabling TCON. TCON is always
disabled first before new mode is set.
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180301213442.16677-7-jernej.skrabec@siol.net

Both TCON clocks are very sensitive to clock changes, since any change
might lead to improper timings.

Make sure our rate is never changed.
Tested-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d5224d2e81ecf73dc09f234e580ada52c00eaee3.1519204731.git-series.maxime.ripard@bootlin.com

I noticed that with 4.16-rc1 LVDS output on A83T based TBS A711 tablet doesn't
work (there's output but it's garbled). I compared some older patches for LVDS
support with the mainlined ones and this change is missing from mainline Linux.

I don't know what the register does exactly and the harcoded register value
doesn't inspire much confidence that it will work in a general case, so I'm
sending this RFC.

This patch fixes the issue on A83T.
Signed-off-by: NOndrej Jirman <megous@megous.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180222161217.23904-1-megous@megous.com

Differently from other Lcd signals, HSYNC and VSYNC signals
result inverted if their bits are cleared to 0.

Invert their settings of IO_POL register.
Signed-off-by: NGiulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1518717288-123578-1-git-send-email-giulio.benetti@micronovasrl.com

This TCON is connected to HDMI encoder.
Acked-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214200906.31509-9-jernej.skrabec@siol.net

Some TCONs on newer SoCs doesn't support channel 0, since they are meant
to be used only with TV or HDMI encoder.

Prepare support for them with adding has_channel_0 quirk.
Acked-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NJernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214200906.31509-8-jernej.skrabec@siol.net

In some cases, the display engine needs to apply some quirks during the
VBLANK event. In the Display Engine 1.0 case for example, we can only
disable the frontend once the backend has been, which is at VBLANK.

Let's introduce a callback that can be implemented by the various engines.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7c298d43aa1500196aa5d15d7a7c0f228c7a6f3c.1516613040.git-series.maxime.ripard@free-electrons.com

We accidentally passed the wrong variable to PTR_ERR().

Fixes: a0c1214e ("drm/sun4i: Add LVDS support")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180115081113.wlam5wkmdynisf4r@mwanda

Add support for the A83T display pipeline.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/614b430adf3a67320362a75c01b01bd53013da8a.1513854122.git-series.maxime.ripard@free-electrons.com

The TCON supports the LVDS interface to output to a panel or a bridge.
Let's add support for it.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7fbb85f33ee1d5009fde4f0d7d236e11ca58b114.1513854122.git-series.maxime.ripard@free-electrons.com

The various outputs the TCON can provide have different constraints on the
dotclock divider. Let's make them configurable by the various mode_set
functions.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/92ff5881c8f8674056d34458b2f264cd48d4e136.1513854122.git-series.maxime.ripard@free-electrons.com

The commit 4c7f16d1 ("drm/sun4i: Fix TCON clock and regmap
initialization sequence") moved a bunch of logic around, but forgot to
update the gotos after the introduction of the err_free_dotclock label.

It means that if we fail later that the one introduced in that commit,
we'll just to the old label which isn't free the clock we created. This
will result in a breakage as soon as someone tries to do something with
that clock, since its resources will have been long reclaimed.

Cc: <stable@vger.kernel.org>
Fixes: 4c7f16d1 ("drm/sun4i: Fix TCON clock and regmap initialization sequence")
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f83c1cebc731f0b4251f5ddd7b38c718cd79bb0b.1512662253.git-series.maxime.ripard@free-electrons.com

The sun4i DRM driver maintains a list of compatible strings it uses to
check if a device node within the display component graph is a TCON.
The TCON driver also has this list, used to bind the TCON driver to
the device. These two lists are identical.

Instead of maintaining two identical lists, export the list from the
TCON driver for the DRM driver to use.
Suggested-by: NRob Herring <robh@kernel.org>
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171127084632.25511-1-wens@csie.org

The A20 display pipeline has 2 frontends, 2 backends, and 2 TCONs.
This patch adds support (or a compatible string in the frontend's
case) for these components.

The TCONs support directly outputting to CPU/RGB/LVDS LCD panels,
or it can output to HDMI via an on-chip HDMI controller, or
CVBS/YPbPr/VGA signals via on-chip TV encoders. These additional
encoders are not covered in this patch.
Signed-off-by: NJonathan Liu <net147@gmail.com>
[wens@csie.org: Expand commit message]
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171017121807.2994-6-wens@csie.org

The A10 has two TCONs that are similar to the ones found on other SoCs.
Like the A31, TCON0 has a register used to mux the TCON outputs to the
downstream encoders. The bit fields are slightly different.
Signed-off-by: NJonathan Liu <net147@gmail.com>
[wens@csie.org: Reworked for A10 and fixed up commit message]
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171017121807.2994-3-wens@csie.org

Some channel0 setup has to be done, no matter what the output interface is
(RGB, CPU, LVDS). Move that code into a common function in order to avoid
duplication.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/183100/

Just like we did for the TCON enable and disable, for historical reasons we
used to rely on the encoders calling the TCON mode_set function, while the
CRTC has a callback for that.

Let's implement it in order to reduce the boilerplate code.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/faa3a4d511039af1d116270dfef3a8b60ca3591e.1508231063.git-series.maxime.ripard@free-electrons.com

So far, we've required all the TCON-connected encoders to call the TCON
enable and disable functions.

This was made this way because in the RGB/LVDS case, the TCON is the CRTC
and the encoder. However, in all the other cases (HDMI, TV, DSI, etc.), we
have another encoder down the road that needs to be programmed.

We also needed to know which channel the encoder is connected to, which is
encoder-specific.

The CRTC's enable and disable callbacks can work just fine for our use
case, and we can get the channel to use just by looking at the type of
encoder, since that is fixed. Implement those callbacks, which will
remove some of the encoder boilerplate.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/90b4396e19b3eca61b2ebfdae0672074b88ad74d.1508231063.git-series.maxime.ripard@free-electrons.com

The drm_display_mode pointer can be mark const, so let's do it.
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e6f92f126640aa6de639386f9b4677db3d8bb37b.1508231063.git-series.maxime.ripard@free-electrons.com