drm/panel: st7703: Pick different reset sequence

[ Upstream commit d12d635bb03c7cb4830acb641eb176ee9ff2aa89 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

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

@@ -428,29 +428,30 @@ static int st7703_prepare(struct drm_panel *panel)
 		return 0;
 
 	dev_dbg(ctx->dev, "Resetting the panel\n");
-	ret = regulator_enable(ctx->vcc);
-	if (ret < 0) {
-		dev_err(ctx->dev, "Failed to enable vcc supply: %d\n", ret);
-		return ret;
-	}
+	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
+
 	ret = regulator_enable(ctx->iovcc);
 	if (ret < 0) {
 		dev_err(ctx->dev, "Failed to enable iovcc supply: %d\n", ret);
-		goto disable_vcc;
+		return ret;
 	}
 
-	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
-	usleep_range(20, 40);
+	ret = regulator_enable(ctx->vcc);
+	if (ret < 0) {
+		dev_err(ctx->dev, "Failed to enable vcc supply: %d\n", ret);
+		regulator_disable(ctx->iovcc);
+		return ret;
+	}
+
+	/* 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 int st7703_get_modes(struct drm_panel *panel,