Add support for setting the I2C bus speed in fsl_i2c.c

Add support to the Freescale I2C driver (fsl_i2c.c) for setting and querying
the I2C bus speed.  Current 8[356]xx boards define the CFG_I2C_SPEED macro,
but fsl_i2c.c ignores it and uses conservative value when programming the
I2C bus speed.

Signed-off-by: Timur Tabi <timur@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>

drivers/i2c/fsl_i2c.c

@@ -32,6 +32,8 @@
 #define I2C_READ_BIT  1
 #define I2C_WRITE_BIT 0
 
+DECLARE_GLOBAL_DATA_PTR;
+
 /* Initialize the bus pointer to whatever one the SPD EEPROM is on.
  * Default is bus 0.  This is necessary because the DDR initialization
  * runs from ROM, and we can't switch buses because we can't modify
@@ -43,24 +45,111 @@ static unsigned int i2c_bus_num __attribute__ ((section ("data"))) = CFG_SPD_BUS
 static unsigned int i2c_bus_num __attribute__ ((section ("data"))) = 0;
 #endif
 
-static volatile struct fsl_i2c *i2c_dev[2] = {
+static unsigned int i2c_bus_speed[2] = {CFG_I2C_SPEED, CFG_I2C_SPEED};
+
+static const struct fsl_i2c *i2c_dev[2] = {
 	(struct fsl_i2c *) (CFG_IMMR + CFG_I2C_OFFSET),
 #ifdef CFG_I2C2_OFFSET
 	(struct fsl_i2c *) (CFG_IMMR + CFG_I2C2_OFFSET)
 #endif
 };
 
+/* I2C speed map for a DFSR value of 1 */
+
+/*
+ * Map I2C frequency dividers to FDR and DFSR values
+ *
+ * This structure is used to define the elements of a table that maps I2C
+ * frequency divider (I2C clock rate divided by I2C bus speed) to a value to be
+ * programmed into the Frequency Divider Ratio (FDR) and Digital Filter
+ * Sampling Rate (DFSR) registers.
+ *
+ * The actual table should be defined in the board file, and it must be called
+ * fsl_i2c_speed_map[].
+ *
+ * The last entry of the table must have a value of {-1, X}, where X is same
+ * FDR/DFSR values as the second-to-last entry.  This guarantees that any
+ * search through the array will always find a match.
+ *
+ * The values of the divider must be in increasing numerical order, i.e.
+ * fsl_i2c_speed_map[x+1].divider > fsl_i2c_speed_map[x].divider.
+ *
+ * For this table, the values are based on a value of 1 for the DFSR
+ * register.  See the application note AN2919 "Determining the I2C Frequency
+ * Divider Ratio for SCL"
+ */
+static const struct {
+	unsigned short divider;
+	u8 dfsr;
+	u8 fdr;
+} fsl_i2c_speed_map[] = {
+	{160, 1, 32}, {192, 1, 33}, {224, 1, 34}, {256, 1, 35},
+	{288, 1, 0}, {320, 1, 1}, {352, 6, 1}, {384, 1, 2}, {416, 6, 2},
+	{448, 1, 38}, {480, 1, 3}, {512, 1, 39}, {544, 11, 3}, {576, 1, 4},
+	{608, 22, 3}, {640, 1, 5}, {672, 32, 3}, {704, 11, 5}, {736, 43, 3},
+	{768, 1, 6}, {800, 54, 3}, {832, 11, 6}, {896, 1, 42}, {960, 1, 7},
+	{1024, 1, 43}, {1088, 22, 7}, {1152, 1, 8}, {1216, 43, 7}, {1280, 1, 9},
+	{1408, 22, 9}, {1536, 1, 10}, {1664, 22, 10}, {1792, 1, 46},
+	{1920, 1, 11}, {2048, 1, 47}, {2176, 43, 11}, {2304, 1, 12},
+	{2560, 1, 13}, {2816, 43, 13}, {3072, 1, 14}, {3328, 43, 14},
+	{3584, 1, 50}, {3840, 1, 15}, {4096, 1, 51}, {4608, 1, 16},
+	{5120, 1, 17}, {6144, 1, 18}, {7168, 1, 54}, {7680, 1, 19},
+	{8192, 1, 55}, {9216, 1, 20}, {10240, 1, 21}, {12288, 1, 22},
+	{14336, 1, 58}, {15360, 1, 23}, {16384, 1, 59}, {18432, 1, 24},
+	{20480, 1, 25}, {24576, 1, 26}, {28672, 1, 62}, {30720, 1, 27},
+	{32768, 1, 63}, {36864, 1, 28}, {40960, 1, 29}, {49152, 1, 30},
+	{61440, 1, 31}, {-1, 1, 31}
+};
+
+/**
+ * Set the I2C bus speed for a given I2C device
+ *
+ * @param dev: the I2C device
+ * @i2c_clk: I2C bus clock frequency
+ * @speed: the desired speed of the bus
+ *
+ * The I2C device must be stopped before calling this function.
+ *
+ * The return value is the actual bus speed that is set.
+ */
+static unsigned int set_i2c_bus_speed(const struct fsl_i2c *dev,
+	unsigned int i2c_clk, unsigned int speed)
+{
+	unsigned short divider = min(i2c_clk / speed, (unsigned short) -1);
+	unsigned int i;
+	u8 fdr, dfsr;
+
+	/*
+	 * We want to choose an FDR/DFSR that generates an I2C bus speed that
+	 * is equal to or lower than the requested speed.  That means that we
+	 * want the first divider that is equal to or greater than the
+	 * calculated divider.
+	 */
+
+	for (i = 0; i < ARRAY_SIZE(fsl_i2c_speed_map); i++)
+		if (fsl_i2c_speed_map[i].divider >= divider) {
+			dfsr = fsl_i2c_speed_map[i].dfsr;
+			fdr = fsl_i2c_speed_map[i].fdr;
+			speed = i2c_clk / fsl_i2c_speed_map[i].divider;
+			break;
+		}
+
+	writeb(fdr, &dev->fdr);			/* set bus speed */
+	writeb(dfsr, &dev->dfsrr);		/* set default filter */
+
+	return speed;
+}
+
 void
 i2c_init(int speed, int slaveadd)
 {
-	volatile struct fsl_i2c *dev;
+	struct fsl_i2c *dev;
 
 	dev = (struct fsl_i2c *) (CFG_IMMR + CFG_I2C_OFFSET);
 
 	writeb(0, &dev->cr);			/* stop I2C controller */
 	udelay(5);				/* let it shutdown in peace */
-	writeb(0x3F, &dev->fdr);		/* set bus speed */
-	writeb(0x3F, &dev->dfsrr);		/* set default filter */
+	i2c_bus_speed[0] = set_i2c_bus_speed(dev, gd->i2c1_clk, speed);
 	writeb(slaveadd << 1, &dev->adr);	/* write slave address */
 	writeb(0x0, &dev->sr);			/* clear status register */
 	writeb(I2C_CR_MEN, &dev->cr);		/* start I2C controller */
@@ -70,12 +159,11 @@ i2c_init(int speed, int slaveadd)
 
 	writeb(0, &dev->cr);			/* stop I2C controller */
 	udelay(5);				/* let it shutdown in peace */
-	writeb(0x3F, &dev->fdr);		/* set bus speed */
-	writeb(0x3F, &dev->dfsrr);		/* set default filter */
+	i2c_bus_speed[1] = set_i2c_bus_speed(dev, gd->i2c2_clk, speed);
 	writeb(slaveadd << 1, &dev->adr);	/* write slave address */
 	writeb(0x0, &dev->sr);			/* clear status register */
 	writeb(I2C_CR_MEN, &dev->cr);		/* start I2C controller */
-#endif	/* CFG_I2C2_OFFSET */
+#endif
 }
 
 static __inline__ int
@@ -279,7 +367,14 @@ int i2c_set_bus_num(unsigned int bus)
 
 int i2c_set_bus_speed(unsigned int speed)
 {
-	return -1;
+	unsigned int i2c_clk = (i2c_bus_num == 1) ? gd->i2c2_clk : gd->i2c1_clk;
+
+	writeb(0, &i2c_dev[i2c_bus_num]->cr);		/* stop controller */
+	i2c_bus_speed[i2c_bus_num] =
+		set_i2c_bus_speed(i2c_dev[i2c_bus_num], i2c_clk, speed);
+	writeb(I2C_CR_MEN, &i2c_dev[i2c_bus_num]->cr);	/* start controller */
+
+	return 0;
 }
 
 unsigned int i2c_get_bus_num(void)
@@ -289,7 +384,8 @@ unsigned int i2c_get_bus_num(void)
 
 unsigned int i2c_get_bus_speed(void)
 {
-	return 0;
+	return i2c_bus_speed[i2c_bus_num];
 }
+
 #endif /* CONFIG_HARD_I2C */
 #endif /* CONFIG_FSL_I2C */