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mvtwsi: Fix clock programming 

The TWSI_FREQUENCY macro was wrong in 2 ways:
1) It was casting the result of the calculations to an u8, while i2c clk
rates are often >= 100Khz which won't fit in a u8, drop the cast.
2) It had an extra factor of 2 in the divider which neither the datasheet nor
the Linux driver have.

The comment for the default value was wrongly saying that m lives in
bits 4-7, while in reality it is in bits 3-6, as can be seen from the correct
shift by 3 used in i2c_init().

While at it remove the unused twsi_actual_speed variable.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
This commit is contained in:
Hans de Goede 2014-05-03 17:46:26 +02:00 committed by Heiko Schocher
parent 557a331908
commit fab356a0b8
1 changed files with 2 additions and 5 deletions
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7
drivers/i2c/mvtwsi.c
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@ -216,7 +216,7 @@ static int twsi_stop(int status)
*/ */
#define TWSI_FREQUENCY(m, n) \ #define TWSI_FREQUENCY(m, n) \
((u8) (CONFIG_SYS_TCLK / (10 * (m + 1) * 2 * (1 << n)))) (CONFIG_SYS_TCLK / (10 * (m + 1) * (1 << n)))
/* /*
* These are required to be reprogrammed before enabling the controller * These are required to be reprogrammed before enabling the controller
@ -225,10 +225,8 @@ static int twsi_stop(int status)
* twsi_slave_address left uninitialized lest checkpatch.pl complains. * twsi_slave_address left uninitialized lest checkpatch.pl complains.
*/ */
/* Baudrate generator: m (bits 7..4) =4, n (bits 3..0) =4 */ /* Baudrate generator: m (bits 6..3) = 8, n (bits 2..0) = 4 */
static u8 twsi_baud_rate = 0x44; /* baudrate at controller reset */ static u8 twsi_baud_rate = 0x44; /* baudrate at controller reset */
/* Default frequency corresponding to default m=4, n=4 */
static u8 twsi_actual_speed = TWSI_FREQUENCY(4, 4);
/* Default slave address is 0 (so is an uninitialized static) */ /* Default slave address is 0 (so is an uninitialized static) */
static u8 twsi_slave_address; static u8 twsi_slave_address;
@ -279,7 +277,6 @@ void i2c_init(int requested_speed, int slaveadd)
} }
/* save baud rate and slave for later calls to twsi_reset */ /* save baud rate and slave for later calls to twsi_reset */
twsi_baud_rate = baud; twsi_baud_rate = baud;
twsi_actual_speed = highest_speed;
twsi_slave_address = slaveadd; twsi_slave_address = slaveadd;
/* reset controller */ /* reset controller */
twsi_reset(); twsi_reset();