drm/imx: imx-ldb: disable LDB on driver bind

BugLink: https://bugs.launchpad.net/bugs/1792392

[ Upstream commit b5826239 ]

The LVDS signal integrity is only guaranteed when the correct enable
sequence (first IPU DI, then LDB) is used. If the LDB display output was
active before the imx-drm driver is loaded (like when a bootsplash was
active) the DI will be disabled by the full IPU reset we do when loading
the driver. The LDB control registers are not part of the IPU range and
thus will remain unchanged.

This leads to the LDB still being active when the DI is getting enabled,
effectively reversing the required enable sequence. Fix this by also
disabling the LDB on driver bind.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/gpu/drm/imx/imx-ldb.c

@@ -526,6 +526,9 @@ static int imx_ldb_bind(struct device *dev, struct device *master, void *data)
 		return PTR_ERR(imx_ldb->regmap);
 	}
 
+	/* disable LDB by resetting the control register to POR default */
+	regmap_write(imx_ldb->regmap, IOMUXC_GPR2, 0);
+
 	imx_ldb->dev = dev;
 
 	if (of_id)