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([2804:14c:485:4b61:8863:100d:2a2a:9a74]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11b060885d8sm66885134c88.2.2025.11.18.05.24.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Nov 2025 05:24:21 -0800 (PST) From: Fabio Estevam To: neil.armstrong@linaro.org Cc: Laurent.pinchart@ideasonboard.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org, imx@lists.linux.dev, Fabio Estevam Subject: [PATCH 2/2] drm/bridge: fsl-ldb: Allow the termination resistor to be enabled Date: Tue, 18 Nov 2025 10:22:08 -0300 Message-Id: <20251118132208.143315-2-festevam@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20251118132208.143315-1-festevam@gmail.com> References: <20251118132208.143315-1-festevam@gmail.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 "nxp,termination-resistor" optional property 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 --- 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,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