Before this patch, booting to Linux VT and doing a simple:

  echo 2 > /sys/class/graphics/fb0/blank
  echo 0 > /sys/class/graphics/fb0/blank

would result in failures to re-enable the panel. Mode set callback is
called only once during boot in this scenario, while calls to
enable/disable callbacks are balanced afterwards. The driver doesn't
work unless userspace calls modeset before enabling the CRTC/connector.

This patch moves enabling of the DSI host from mode_set into pre_enable
callback, and removes some old hacks where this bridge driver is
directly calling into other bridge driver's callbacks.

pre_enable_prev_first flag is set on the panel's bridge so that panel
drivers will get their prepare function called between DSI host's
pre_enable and enable callbacks, so that they get a chance to
perform panel setup while DSI host is already enabled in command
mode. Otherwise panel's prepare would be called before DSI host
is enabled, and any DSI communication used in prepare callback
would fail.

With all these changes, the enable/disable sequence is now well
balanced, and host's and panel's callbacks are called in proper order
documented in the drm_panel API documentation without needing the old
hacks. (Mainly that panel->prepare is called when DSI host is ready to
allow the panel driver to send DSI commands and vice versa during
disable.)

Tested on Pinephone Pro. Trace of the callbacks follows.

Before:

[    1.253882] dw-mipi-dsi-rockchip ff960000.dsi: mode_set
[    1.290732] panel-himax-hx8394 ff960000.dsi.0: prepare
[    1.475576] dw-mipi-dsi-rockchip ff960000.dsi: enable
[    1.475593] panel-himax-hx8394 ff960000.dsi.0: enable

echo 2 > /sys/class/graphics/fb0/blank

[   13.722799] panel-himax-hx8394 ff960000.dsi.0: disable
[   13.774502] dw-mipi-dsi-rockchip ff960000.dsi: post_disable
[   13.774526] panel-himax-hx8394 ff960000.dsi.0: unprepare

echo 0 > /sys/class/graphics/fb0/blank

[   17.735796] panel-himax-hx8394 ff960000.dsi.0: prepare
[   17.923522] dw-mipi-dsi-rockchip ff960000.dsi: enable
[   17.923540] panel-himax-hx8394 ff960000.dsi.0: enable
[   17.944330] dw-mipi-dsi-rockchip ff960000.dsi: failed to write command FIFO
[   17.944335] panel-himax-hx8394 ff960000.dsi.0: sending command 0xb9 failed: -110
[   17.944340] panel-himax-hx8394 ff960000.dsi.0: Panel init sequence failed: -110

echo 2 > /sys/class/graphics/fb0/blank

[  431.148583] panel-himax-hx8394 ff960000.dsi.0: disable
[  431.169259] dw-mipi-dsi-rockchip ff960000.dsi: failed to write command FIFO
[  431.169268] panel-himax-hx8394 ff960000.dsi.0: Failed to enter sleep mode: -110
[  431.169282] dw-mipi-dsi-rockchip ff960000.dsi: post_disable
[  431.169316] panel-himax-hx8394 ff960000.dsi.0: unprepare
[  431.169357] pclk_mipi_dsi0 already disabled

echo 0 > /sys/class/graphics/fb0/blank

[  432.796851] panel-himax-hx8394 ff960000.dsi.0: prepare
[  432.981537] dw-mipi-dsi-rockchip ff960000.dsi: enable
[  432.981568] panel-himax-hx8394 ff960000.dsi.0: enable
[  433.002290] dw-mipi-dsi-rockchip ff960000.dsi: failed to write command FIFO
[  433.002299] panel-himax-hx8394 ff960000.dsi.0: sending command 0xb9 failed: -110
[  433.002312] panel-himax-hx8394 ff960000.dsi.0: Panel init sequence failed: -110

-----------------------------------------------------------------------

After:

[    1.248372] dw-mipi-dsi-rockchip ff960000.dsi: mode_set
[    1.248704] dw-mipi-dsi-rockchip ff960000.dsi: pre_enable
[    1.285377] panel-himax-hx8394 ff960000.dsi.0: prepare
[    1.468392] dw-mipi-dsi-rockchip ff960000.dsi: enable
[    1.468421] panel-himax-hx8394 ff960000.dsi.0: enable

echo 2 > /sys/class/graphics/fb0/blank

[   16.210357] panel-himax-hx8394 ff960000.dsi.0: disable
[   16.261315] dw-mipi-dsi-rockchip ff960000.dsi: post_disable
[   16.261339] panel-himax-hx8394 ff960000.dsi.0: unprepare

echo 0 > /sys/class/graphics/fb0/blank

[   19.161453] dw-mipi-dsi-rockchip ff960000.dsi: pre_enable
[   19.197869] panel-himax-hx8394 ff960000.dsi.0: prepare
[   19.382141] dw-mipi-dsi-rockchip ff960000.dsi: enable
[   19.382158] panel-himax-hx8394 ff960000.dsi.0: enable

       (But depends on functionality intorduced in Linux 6.3, so this patch will
        not build on older kernels when applied to older stable branches.)

Fixes: 46fc5154 ("drm/bridge/synopsys: Add MIPI DSI host controller bridge")
Signed-off-by: Ondrej Jirman <megi@xff.cz>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230617224915.1923630-1-megi@xff.cz