i2c: Blackfin TWI: make sure we don't end up with a CLKDIV=0

Make sure we don't end up with an invalid CLKDIV=0 in case someone
specifies 20kHz SCL or less (5 * 1024 / 20 = 0x100).

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
[ben-linux@fluff.org: shortened subject line]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

drivers/i2c/busses/Kconfig

@@ -298,7 +298,7 @@ config I2C_BLACKFIN_TWI
 config I2C_BLACKFIN_TWI_CLK_KHZ
 	int "Blackfin TWI I2C clock (kHz)"
 	depends on I2C_BLACKFIN_TWI
-	range 10 400
+	range 21 400
 	default 50
 	help
 	  The unit of the TWI clock is kHz.

drivers/i2c/busses/i2c-bfin-twi.c

@@ -614,6 +614,7 @@ static int i2c_bfin_twi_probe(struct platform_device *pdev)
 	struct i2c_adapter *p_adap;
 	struct resource *res;
 	int rc;
+	unsigned int clkhilow;
 
 	iface = kzalloc(sizeof(struct bfin_twi_iface), GFP_KERNEL);
 	if (!iface) {
@@ -675,10 +676,14 @@ static int i2c_bfin_twi_probe(struct platform_device *pdev)
 	/* Set TWI internal clock as 10MHz */
 	write_CONTROL(iface, ((get_sclk() / 1024 / 1024 + 5) / 10) & 0x7F);
 
+	/*
+	 * We will not end up with a CLKDIV=0 because no one will specify
+	 * 20kHz SCL or less in Kconfig now. (5 * 1024 / 20 = 0x100)
+	 */
+	clkhilow = 5 * 1024 / CONFIG_I2C_BLACKFIN_TWI_CLK_KHZ;
+
 	/* Set Twi interface clock as specified */
-	write_CLKDIV(iface, ((5*1024 / CONFIG_I2C_BLACKFIN_TWI_CLK_KHZ)
-			<< 8) | ((5*1024 / CONFIG_I2C_BLACKFIN_TWI_CLK_KHZ)
-			& 0xFF));
+	write_CLKDIV(iface, (clkhilow << 8) | clkhilow);
 
 	/* Enable TWI */
 	write_CONTROL(iface, read_CONTROL(iface) | TWI_ENA);