Support non-standard I2C timings on Pi 5

arch/arm/boot/dts/rp1.dtsi

@@ -305,12 +305,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C0 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -319,12 +315,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C1 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -333,12 +325,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C2 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -347,12 +335,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C3 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -361,12 +345,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C4 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -375,12 +355,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C5 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 
@@ -389,12 +365,8 @@
 			compatible = "snps,designware-i2c";
 			interrupts = <RP1_INT_I2C6 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&rp1_clocks RP1_CLK_SYS>;
-			snps,ss_hcnt = <978>;
-			snps,ss_lcnt = <990>;
-			snps,fs_hcnt = <200>;
-			snps,fs_lcnt = <268>;
-			snps,fp_hcnt = <60>;
-			snps,fp_lcnt = <107>;
+			i2c-scl-rising-time-ns = <65>;
+			i2c-scl-falling-time-ns = <100>;
 			status = "disabled";
 		};
 

drivers/i2c/busses/i2c-designware-common.c

@@ -318,6 +318,9 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
 {
 	u32 acpi_speed = i2c_dw_acpi_round_bus_speed(dev->dev);
 	struct i2c_timings *t = &dev->timings;
+	u32 wanted_speed;
+	u32 legal_speed = 0;
+	int i;
 
 	/*
 	 * Find bus speed from the "clock-frequency" device property, ACPI
@@ -329,6 +332,30 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
 		t->bus_freq_hz = max(t->bus_freq_hz, acpi_speed);
 	else
 		t->bus_freq_hz = I2C_MAX_FAST_MODE_FREQ;
+
+	wanted_speed = t->bus_freq_hz;
+
+	/* For unsupported speeds, scale down the lowest speed which is faster. */
+	for (i = 0; i < ARRAY_SIZE(supported_speeds); i++) {
+		/* supported speeds is in decreasing order */
+		if (wanted_speed == supported_speeds[i]) {
+			legal_speed = 0;
+			break;
+		}
+		if (wanted_speed > supported_speeds[i])
+			break;
+
+		legal_speed = supported_speeds[i];
+	}
+
+	if (legal_speed) {
+		/*
+		 * Pretend this was the requested speed, but preserve the preferred
+		 * speed so the clock counts can be scaled.
+		 */
+		t->bus_freq_hz = legal_speed;
+		dev->wanted_bus_speed = wanted_speed;
+	}
 }
 EXPORT_SYMBOL_GPL(i2c_dw_adjust_bus_speed);
 

drivers/i2c/busses/i2c-designware-core.h

@@ -287,6 +287,7 @@ struct dw_i2c_dev {
 	u16			fp_lcnt;
 	u16			hs_hcnt;
 	u16			hs_lcnt;
+	u32			wanted_bus_speed;
 	int			(*acquire_lock)(void);
 	void			(*release_lock)(void);
 	int			semaphore_idx;

drivers/i2c/busses/i2c-designware-master.c

@@ -37,13 +37,30 @@ static void i2c_dw_configure_fifo_master(struct dw_i2c_dev *dev)
 	regmap_write(dev->map, DW_IC_CON, dev->master_cfg);
 }
 
+static u16 clock_calc(struct dw_i2c_dev *dev, bool want_high)
+{
+	struct i2c_timings *t = &dev->timings;
+	u32 wanted_speed = dev->wanted_bus_speed ?: t->bus_freq_hz;
+	u32 clk_khz = i2c_dw_clk_rate(dev);
+	u32 extra_ns = want_high ? t->scl_fall_ns : t->scl_rise_ns;
+	u32 extra_cycles = (u32)((u64)clk_khz * extra_ns / 1000000);
+	u32 period = ((u64)clk_khz * 1000 + wanted_speed - 1) / wanted_speed;
+	u32 cycles = (period + want_high)/2 - extra_cycles;
+
+	if (cycles > 0xffff)
+		cycles = 0xffff;
+
+	return (u16)cycles;
+}
+
 static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 {
 	u32 comp_param1;
 	u32 sda_falling_time, scl_falling_time;
 	struct i2c_timings *t = &dev->timings;
 	const char *fp_str = "";
 	u32 ic_clk;
+	u32 hcnt, lcnt;
 	int ret;
 
 	ret = i2c_dw_acquire_lock(dev);
@@ -59,6 +76,9 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 	sda_falling_time = t->sda_fall_ns ?: 300; /* ns */
 	scl_falling_time = t->scl_fall_ns ?: 300; /* ns */
 
+	hcnt = clock_calc(dev, true);
+	lcnt = clock_calc(dev, false);
+
 	/* Calculate SCL timing parameters for standard mode if not set */
 	if (!dev->ss_hcnt || !dev->ss_lcnt) {
 		ic_clk = i2c_dw_clk_rate(dev);
@@ -74,6 +94,8 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 					scl_falling_time,
 					0);	/* No offset */
 	}
+	dev->ss_hcnt = hcnt;
+	dev->ss_lcnt = lcnt;
 	dev_dbg(dev->dev, "Standard Mode HCNT:LCNT = %d:%d\n",
 		dev->ss_hcnt, dev->ss_lcnt);
 
@@ -124,6 +146,8 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 					scl_falling_time,
 					0);	/* No offset */
 	}
+	dev->fs_hcnt = hcnt;
+	dev->fs_lcnt = lcnt;
 	dev_dbg(dev->dev, "Fast Mode%s HCNT:LCNT = %d:%d\n",
 		fp_str, dev->fs_hcnt, dev->fs_lcnt);
 
@@ -152,6 +176,8 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 						scl_falling_time,
 						0);	/* No offset */
 		}
+		dev->hs_hcnt = hcnt;
+		dev->hs_lcnt = lcnt;
 		dev_dbg(dev->dev, "High Speed Mode HCNT:LCNT = %d:%d\n",
 			dev->hs_hcnt, dev->hs_lcnt);
 	}

drivers/i2c/busses/i2c-designware-platdrv.c

@@ -132,18 +132,9 @@ static int mscc_twi_set_sda_hold_time(struct dw_i2c_dev *dev)
 	return 0;
 }
 
-static void dw_i2c_read_of_cnt(struct device_node *np, const char *name, u16 *pval)
-{
-	u32 val;
-
-	if (!of_property_read_u32(np, name, &val))
-		*pval = (u16)val;
-}
-
 static int dw_i2c_of_configure(struct platform_device *pdev)
 {
 	struct dw_i2c_dev *dev = platform_get_drvdata(pdev);
-	struct device_node *np = pdev->dev.of_node;
 
 	switch (dev->flags & MODEL_MASK) {
 	case MODEL_MSCC_OCELOT:
@@ -155,15 +146,6 @@ static int dw_i2c_of_configure(struct platform_device *pdev)
 		break;
 	}
 
-	dw_i2c_read_of_cnt(np, "snps,ss_hcnt", &dev->ss_hcnt);
-	dw_i2c_read_of_cnt(np, "snps,ss_lcnt", &dev->ss_lcnt);
-	dw_i2c_read_of_cnt(np, "snps,fs_hcnt", &dev->fs_hcnt);
-	dw_i2c_read_of_cnt(np, "snps,fs_lcnt", &dev->fs_lcnt);
-	dw_i2c_read_of_cnt(np, "snps,fp_hcnt", &dev->fp_hcnt);
-	dw_i2c_read_of_cnt(np, "snps,fp_lcnt", &dev->fp_lcnt);
-	dw_i2c_read_of_cnt(np, "snps,hs_hcnt", &dev->hs_hcnt);
-	dw_i2c_read_of_cnt(np, "snps,hs_lcnt", &dev->hs_lcnt);
-
 	return 0;
 }