drm/panel: st7703: Pick different reset sequence

Switching to a different reset sequence, enabling IOVCC before enabling
VCC.

There also needs to be a delay after enabling the supplies and before
deasserting the reset. The datasheet specifies 1ms after the supplies
reach the required voltage. Use 10-20ms to also give the power supplies
some time to reach the required voltage, too.

This fixes intermittent panel initialization failures and screen
corruption during resume from sleep on panel xingbangda,xbd599 (e.g.
used in PinePhone).
Signed-off-by: Ondrej Jirman <megi@xff.cz>
Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Reported-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Tested-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230211171748.36692-2-frank@oltmanns.dev

drivers/gpu/drm/panel/panel-sitronix-st7703.c

@@ -506,29 +506,30 @@ static int st7703_prepare(struct drm_panel *panel)
 		return 0;
 
 	dev_dbg(ctx->dev, "Resetting the panel\n");
-	ret = regulator_enable(ctx->vcc);
+	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
+
+	ret = regulator_enable(ctx->iovcc);
 	if (ret < 0) {
-		dev_err(ctx->dev, "Failed to enable vcc supply: %d\n", ret);
+		dev_err(ctx->dev, "Failed to enable iovcc supply: %d\n", ret);
 		return ret;
 	}
-	ret = regulator_enable(ctx->iovcc);
+
+	ret = regulator_enable(ctx->vcc);
 	if (ret < 0) {
-		dev_err(ctx->dev, "Failed to enable iovcc supply: %d\n", ret);
-		goto disable_vcc;
+		dev_err(ctx->dev, "Failed to enable vcc supply: %d\n", ret);
+		regulator_disable(ctx->iovcc);
+		return ret;
 	}
 
-	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
-	usleep_range(20, 40);
+	/* Give power supplies time to stabilize before deasserting reset. */
+	usleep_range(10000, 20000);
+
 	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
-	msleep(20);
+	usleep_range(15000, 20000);
 
 	ctx->prepared = true;
 
 	return 0;
-
-disable_vcc:
-	regulator_disable(ctx->vcc);
-	return ret;
 }
 
 static const u32 mantix_bus_formats[] = {