The LVDS Control Register (LVDS_CTRL) register has an HS_EN bit that allows the 100 Ohm termination resistor in the chip to be enabled.
Add support to setting the HS_EN bit when the optional property "nxp,enable-termination-resistor" is present. The motivation for introducing this property was a custom i.MX8MP board that was showing visual artifacts. After enabling the 100 Ohm termination resistor the LVDS signal quality improved causing the artifacts to disappear. Signed-off-by: Fabio Estevam <[email protected]> --- Changes since v1: - Change the property name to nxp,enable-termination-resistor (Frank). drivers/gpu/drm/bridge/fsl-ldb.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c index 5c3cf37200bc..b4b9130de32c 100644 --- a/drivers/gpu/drm/bridge/fsl-ldb.c +++ b/drivers/gpu/drm/bridge/fsl-ldb.c @@ -92,6 +92,7 @@ struct fsl_ldb { const struct fsl_ldb_devdata *devdata; bool ch0_enabled; bool ch1_enabled; + bool termination_resistor; }; static bool fsl_ldb_is_dual(const struct fsl_ldb *fsl_ldb) @@ -212,6 +213,10 @@ static void fsl_ldb_atomic_enable(struct drm_bridge *bridge, /* Program LVDS_CTRL */ reg = LVDS_CTRL_CC_ADJ(2) | LVDS_CTRL_PRE_EMPH_EN | LVDS_CTRL_PRE_EMPH_ADJ(3) | LVDS_CTRL_VBG_EN; + + reg &= ~LVDS_CTRL_HS_EN; + if (fsl_ldb->termination_resistor) + reg |= LVDS_CTRL_HS_EN; regmap_write(fsl_ldb->regmap, fsl_ldb->devdata->lvds_ctrl, reg); /* Wait for VBG to stabilize. */ @@ -292,6 +297,7 @@ static const struct drm_bridge_funcs funcs = { static int fsl_ldb_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; + struct device_node *np = dev->of_node; struct device_node *panel_node; struct device_node *remote1, *remote2; struct drm_panel *panel; @@ -340,6 +346,9 @@ static int fsl_ldb_probe(struct platform_device *pdev) if (IS_ERR(panel)) return PTR_ERR(panel); + if (of_property_present(np, "nxp,enable-termination-resistor")) + fsl_ldb->termination_resistor = true; + fsl_ldb->panel_bridge = devm_drm_panel_bridge_add(dev, panel); if (IS_ERR(fsl_ldb->panel_bridge)) return PTR_ERR(fsl_ldb->panel_bridge); -- 2.34.1
