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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lucas Stach <l.stach@pengutronix.de>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.14 012/165] drm/imx: imx-ldb: disable LDB on driver bind
Date:   Mon,  3 Sep 2018 18:54:58 +0200
Message-Id: <20180903165655.622866839@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lucas Stach <l.stach@pengutronix.de>

[ Upstream commit b58262396fabd43dc869b576e3defdd23b32fe94 ]

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>
---
 drivers/gpu/drm/imx/imx-ldb.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/imx/imx-ldb.c
+++ b/drivers/gpu/drm/imx/imx-ldb.c
@@ -612,6 +612,9 @@ static int imx_ldb_bind(struct device *d
 		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)