[PATCH v1 1/1] drm/mediatek/dp: The register is written with the parsed DTS SSC value.

[Liankun Yang]

[Description]
Severe screen flickering has been observed on the external display
when the DP projection function is used with the market expansion dock.

[Root cause]
It has been discovered through analysis that severe screen flickering
will occur when using the current default settings of
SC (Spread Spectrum Clocking) after it is opened.

[Solution]
Reducing SSC capability on the test platform can
resolve the screen flickering issue.

By configuring SSC parameters in DTS, locating the DP SSC node
in phy-mtk-dp, parsing the current value of SSC, and writing this value
into PHY to configure SSC can solve the screen flickering problem.

[Test]
The SSC configuration values are read from DTS, parsed in the driver,
and then written to the hardware. The test results indicate that
there is no screen flickering.

Signed-off-by: Liankun Yang <liankun.yang at mediatek.com>
---
 drivers/phy/mediatek/phy-mtk-dp.c | 61 +++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/drivers/phy/mediatek/phy-mtk-dp.c b/drivers/phy/mediatek/phy-mtk-dp.c
index d7024a144335..13e5d3c33784 100644
--- a/drivers/phy/mediatek/phy-mtk-dp.c
+++ b/drivers/phy/mediatek/phy-mtk-dp.c
@@ -25,6 +25,10 @@
 #define BIT_RATE_HBR2			2
 #define BIT_RATE_HBR3			3
 
+#define MTK_DP_PHY_DIG_GLB_DA_REG_14	(PHY_OFFSET + 0xD8)
+#define XTP_GLB_TXPLL_SSC_DELTA_RBR_DEFAULT	GENMASK(15, 0)
+#define XTP_GLB_TXPLL_SSC_DELTA_HBR_DEFAULT	GENMASK(31, 16)
+
 #define MTK_DP_PHY_DIG_SW_RST		(PHY_OFFSET + 0x38)
 #define DP_GLB_SW_RST_PHYD		BIT(0)
 
@@ -78,10 +82,57 @@
 #define DRIVING_PARAM_8_DEFAULT	(XTP_LN_TX_LCTXCP1_SW2_PRE1_DEFAULT | \
 				 XTP_LN_TX_LCTXCP1_SW3_PRE0_DEFAULT)
 
+#define SSC_SETTING	"dp-ssc-setting"
+#define RG_XTP_GLB_TXPLL_SSC_DELTA_RBR	"ssc-delta-rbr"
+#define RG_XTP_GLB_TXPLL_SSC_DELTA_HBR	"ssc-delta-hbr"
+
 struct mtk_dp_phy {
 	struct regmap *regs;
+	struct device *dev;
 };
 
+static int mtk_dp_set_ssc_config(struct phy *phy, struct mtk_dp_phy *dp_phy,
+		struct device_node *ssc_node, const char *mode_name, u32 ssc_reg_offset)
+{
+	int ret;
+	u32 read_value = 0;
+
+	ret = of_property_read_u32(ssc_node, mode_name, &read_value);
+	if (ret) {
+		dev_err(&phy->dev, "Read fail,DPTX is not %s\n", mode_name);
+		return -EINVAL;
+	}
+
+	if (!read_value) {
+		dev_err(&phy->dev, "Read value is NULL\n");
+		return -ENOMEM;
+	}
+
+	if (!strcmp(mode_name, RG_XTP_GLB_TXPLL_SSC_DELTA_RBR)) {
+		regmap_update_bits(dp_phy->regs, ssc_reg_offset,
+			   XTP_GLB_TXPLL_SSC_DELTA_RBR_DEFAULT, read_value);
+	} else if (!strcmp(mode_name, RG_XTP_GLB_TXPLL_SSC_DELTA_HBR)) {
+		read_value = read_value << 16 | 0x0000;
+		regmap_update_bits(dp_phy->regs, ssc_reg_offset,
+			   XTP_GLB_TXPLL_SSC_DELTA_HBR_DEFAULT, read_value);
+	}
+
+	return 0;
+}
+
+static struct device_node *mtk_dp_get_ssc_node(struct phy *phy, struct mtk_dp_phy *dp_phy)
+{
+	struct device_node *mode_node = NULL;
+
+	mode_node = of_find_node_by_name(dp_phy->dev->of_node, SSC_SETTING);
+	if (!mode_node) {
+		dev_err(&phy->dev, "SSC node is NULL\n");
+		return NULL;
+	}
+
+	return mode_node;
+}
+
 static int mtk_dp_phy_init(struct phy *phy)
 {
 	struct mtk_dp_phy *dp_phy = phy_get_drvdata(phy);
@@ -109,6 +160,7 @@ static int mtk_dp_phy_init(struct phy *phy)
 static int mtk_dp_phy_configure(struct phy *phy, union phy_configure_opts *opts)
 {
 	struct mtk_dp_phy *dp_phy = phy_get_drvdata(phy);
+	struct device_node *ssc_node = NULL;
 	u32 val;
 
 	if (opts->dp.set_rate) {
@@ -137,6 +189,14 @@ static int mtk_dp_phy_configure(struct phy *phy, union phy_configure_opts *opts)
 	regmap_update_bits(dp_phy->regs, MTK_DP_PHY_DIG_PLL_CTL_1,
 			   TPLL_SSC_EN, opts->dp.ssc ? TPLL_SSC_EN : 0);
 
+	ssc_node = mtk_dp_get_ssc_node(phy, dp_phy);
+	if (ssc_node) {
+		mtk_dp_set_ssc_config(phy, dp_phy, ssc_node, RG_XTP_GLB_TXPLL_SSC_DELTA_RBR,
+			MTK_DP_PHY_DIG_GLB_DA_REG_14);
+		mtk_dp_set_ssc_config(phy, dp_phy, ssc_node, RG_XTP_GLB_TXPLL_SSC_DELTA_HBR,
+			MTK_DP_PHY_DIG_GLB_DA_REG_14);
+	}
+
 	return 0;
 }
 
@@ -186,6 +246,7 @@ static int mtk_dp_phy_probe(struct platform_device *pdev)
 	if (!dev->of_node)
 		phy_create_lookup(phy, "dp", dev_name(dev));
 
+	dp_phy->dev = dev;
 	return 0;
 }
 
-- 
2.43.0