[PATCH v2 1/5] drm/panel: feiyang-fy07024di26a30d: Fix prepare error cleanup

[Hsieh Hung-En <hungen3108@gmail.com>]

feiyang_prepare() returns without disabling previously enabled
regulators if enabling AVDD or writing DCS commands fails. Since
drm_panel_prepare() does not mark the panel as prepared on failure,
drm_panel_unprepare() does not call the driver's unprepare() callback,
leaving regulator enable counts elevated even after subsequent
successful prepare/unprepare cycles.

Disable DVDD if enabling AVDD fails. On a DCS write failure, restore
the reset GPIO to its unprepared state and disable both regulators,
preserving the existing 10 ms power-off interval between AVDD and DVDD.

Fixes: 69dc678abc2b ("drm/panel: Add Feiyang FY07024DI26A30-D MIPI-DSI LCD panel")
Reported-by: Douglas Anderson <dianders@chromium.org>
Closes: https://lore.kernel.org/r/CAD=FV=Xm48DUT==8HuuGCSFZtLTEk-W2Q6UTfqt-MnM4nULzTw@mail.gmail.com
Signed-off-by: Hsieh Hung-En <hungen3108@gmail.com>
---

Notes:
    Power sequencing note:
    
    The error path retains the 10 ms AVDD-to-DVDD shutdown interval
    used by unprepare().
    
    The FY07024DI26A30-D datasheet, Section 7.3 (Power, Signal sequence),
    specifies T10 > 0 between AVDD/VGL reaching GND and DVDD starting
    to fall. The delay allows time for AVDD to discharge before disabling
    DVDD, but compliance with T10 has not been verified on hardware.
    
    The existing unprepare() comment associates the delay with T11,
    which actually specifies the DVDD fall time (0 < T11 <= 10 ms).
    That comment can be corrected separately.
    
    The msleep(10) checkpatch warning is expected. T10 has no specified
    upper bound, so a longer sleep does not violate that timing constraint.
    msleep() is retained to match the existing unprepare() sequence.
    
    Datasheet:
    https://files.pine64.org/doc/datasheet/pine64/FY07024DI26A30-D_feiyang_LCD_panel.pdf

 .../gpu/drm/panel/panel-feiyang-fy07024di26a30d.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c b/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
index c1d8ca5ca6e1..bb4cc1ea2ece 100644
--- a/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
+++ b/drivers/gpu/drm/panel/panel-feiyang-fy07024di26a30d.c
@@ -59,7 +59,7 @@ static int feiyang_prepare(struct drm_panel *panel)
 
 	ret = regulator_enable(ctx->avdd);
 	if (ret)
-		return ret;
+		goto disable_dvdd;
 
 	/* T3 (dvdd rise + avdd start + avdd rise) T3 >= 20ms */
 	msleep(20);
@@ -84,10 +84,21 @@ static int feiyang_prepare(struct drm_panel *panel)
 		ret = mipi_dsi_dcs_write_buffer(dsi, cmd->data,
 						FEIYANG_INIT_CMD_LEN);
 		if (ret < 0)
-			return ret;
+			goto assert_reset;
 	}
 
 	return 0;
+
+assert_reset:
+	gpiod_set_value(ctx->reset, 0);
+	regulator_disable(ctx->avdd);
+
+	/* Preserve the AVDD-to-DVDD shutdown delay from unprepare(). */
+	msleep(10);
+
+disable_dvdd:
+	regulator_disable(ctx->dvdd);
+	return ret;
 }
 
 static int feiyang_enable(struct drm_panel *panel)
-- 
2.43.0