[PATCH] drm/panel/panel-sitronix-st7701: Move init sequence from prepare() to enable()

[Mimoja]

The struct drm_panel_funcs are offering a prepare() and an enable()
entrypoint for panels. According to drm/panel.h:

"The .prepare() function is typically called before the display controller
starts to transmit video data."
and
"After the display controller has started transmitting video data, it's safe
 to call the .enable() function."

The st7701 driver currently does not respect this, queing DSI control commands
during enable.
While generally fine this can lead to a fillup of the transmission queue before
the transmission is set up on certain dsi bridges.
This issue can also be seen on downstream imx8m* kernels.
By moving the init sequence into the enable function we not only circumvent the issue
but also properly soft-reset the panel on enable().

Signed-off-by: Mimoja <git at mimoja.de>

Cc: Marek Vasut <marex at denx.de>
Cc: Guido Günther <agx at sigxcpu.org>
Cc: Jagan Teki <jagan at amarulasolutions.com>
Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Cc: Linus Walleij <linus.walleij at linaro.org>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: Thierry Reding <thierry.reding at gmail.com>
---
 drivers/gpu/drm/panel/panel-sitronix-st7701.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7701.c b/drivers/gpu/drm/panel/panel-sitronix-st7701.c
index 7eae83aa0ea1..18c5a8d97cc8 100644
--- a/drivers/gpu/drm/panel/panel-sitronix-st7701.c
+++ b/drivers/gpu/drm/panel/panel-sitronix-st7701.c
@@ -439,6 +439,13 @@ static int st7701_prepare(struct drm_panel *panel)
 	gpiod_set_value(st7701->reset, 1);
 	msleep(150);
 
+	return 0;
+}
+
+static int st7701_enable(struct drm_panel *panel)
+{
+	struct st7701 *st7701 = panel_to_st7701(panel);
+
 	st7701_init_sequence(st7701);
 
 	if (st7701->desc->gip_sequence)
@@ -447,13 +454,6 @@ static int st7701_prepare(struct drm_panel *panel)
 	/* Disable Command2 */
 	st7701_switch_cmd_bkx(st7701, false, 0);
 
-	return 0;
-}
-
-static int st7701_enable(struct drm_panel *panel)
-{
-	struct st7701 *st7701 = panel_to_st7701(panel);
-
 	ST7701_DSI(st7701, MIPI_DCS_SET_DISPLAY_ON, 0x00);
 
 	return 0;
-- 
2.39.2