[PATCH] drm/panel: ilitek-ili9881c: Avoid unbalance prepare/unprepare

[Michael Trimarchi <michael@amarulasolutions.com>]

All the panel driver check the fact that their prepare/unprepare
call was already called. It's not an ideal solution but fix
for now the problem on ili9881c

[ 9862.283296] ------------[ cut here ]------------
[ 9862.288490] unbalanced disables for vcc3v3_lcd
[ 9862.293555] WARNING: CPU: 0 PID: 1 at drivers/regulator/core.c:2851
_regulator_disable+0xd4/0x190

from:

[ 9862.038619]  drm_panel_unprepare+0x2c/0x4c
[ 9862.043212]  panel_bridge_post_disable+0x18/0x24
[ 9862.048390]  dw_mipi_dsi_bridge_post_disable+0x3c/0xf0
[ 9862.054153]  drm_atomic_bridge_chain_post_disable+0x8c/0xd0

and:

[ 9862.183103]  drm_panel_unprepare+0x2c/0x4c
[ 9862.187695]  panel_bridge_post_disable+0x18/0x24
[ 9862.192872]  drm_atomic_bridge_chain_post_disable+0x8c/0xd0
[ 9862.199117]  disable_outputs+0x120/0x31c

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
---
 drivers/gpu/drm/panel/panel-ilitek-ili9881c.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
index 103a16018975..f75eecb0e65c 100644
--- a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
+++ b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
@@ -52,6 +52,8 @@ struct ili9881c {
 
 	struct regulator	*power;
 	struct gpio_desc	*reset;
+
+	bool			prepared;
 };
 
 #define ILI9881C_SWITCH_PAGE_INSTR(_page)	\
@@ -707,6 +709,10 @@ static int ili9881c_prepare(struct drm_panel *panel)
 	unsigned int i;
 	int ret;
 
+	/* Preparing when already prepared is a no-op */
+	if (ctx->prepared)
+		return 0;
+
 	/* Power the panel */
 	ret = regulator_enable(ctx->power);
 	if (ret)
@@ -745,6 +751,8 @@ static int ili9881c_prepare(struct drm_panel *panel)
 	if (ret)
 		return ret;
 
+	ctx->prepared = true;
+
 	return 0;
 }
 
@@ -770,10 +778,16 @@ static int ili9881c_unprepare(struct drm_panel *panel)
 {
 	struct ili9881c *ctx = panel_to_ili9881c(panel);
 
+	/* Unpreparing when already unprepared is a no-op */
+	if (!ctx->prepared)
+		return 0;
+
 	mipi_dsi_dcs_enter_sleep_mode(ctx->dsi);
 	regulator_disable(ctx->power);
 	gpiod_set_value(ctx->reset, 1);
 
+	ctx->prepared = false;
+
 	return 0;
 }
 
-- 
2.25.1