diff options
| author | Neta Zur <neta@marvell.com> | 2017-06-18 14:04:24 +0300 |
|---|---|---|
| committer | Kostya Porotchkin <kostap@marvell.com> | 2017-06-18 14:55:58 +0300 |
| commit | 44114c6c36b85cba804301cc8b90034f55324c0d (patch) | |
| tree | 57ecd3564f3045f3252e3b4e4bfb1e199a265de5 | |
| parent | cb4972fbbbd9fdc65ea02f8602457084a70f757e (diff) | |
i2c: a8k: add comment which describes baudrate settings
Change-Id: I6b62e8ff3089542bd9d1c49ff7f85eab98533deb
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Neta Zur <neta@marvell.com>
Reviewed-on: http://vgitil04.il.marvell.com:8080/40574
Tested-by: iSoC Platform CI <ykjenk@marvell.com>
Reviewed-by: Kostya Porotchkin <kostap@marvell.com>
| -rw-r--r-- | drivers/marvell/i2c/a8k_i2c.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/drivers/marvell/i2c/a8k_i2c.c b/drivers/marvell/i2c/a8k_i2c.c index 1356fc07..c4ef1441 100644 --- a/drivers/marvell/i2c/a8k_i2c.c +++ b/drivers/marvell/i2c/a8k_i2c.c @@ -248,6 +248,20 @@ static int marvell_i2c_address_set(uint8_t chain, int command) return 0; } +/* + * The I2C module contains a clock divider to generate the SCL clock. + * This function calculates and sets the <N> and <M> fields in the I2C Baud + * Rate Register (t=01) to obtain given 'requested_speed'. + * The requested_speed will be equal to: + * CONFIG_SYS_TCLK / (10 * (M + 1) * (2 << N)) + * Where M is the value represented by bits[6:3] and N is the value represented + * by bits[2:0] of "I2C Baud Rate Register". + * Therefore max M which can be set is 16 (2^4) and max N is 8 (2^3). So the + * lowest possible baudrate is: + * CONFIG_SYS_TCLK/(10 * (16 +1) * (2 << 8), which equals to: + * CONFIG_SYS_TCLK/87040. Assuming that CONFIG_SYS_TCLK=250MHz, the lowest + * possible frequency is ~2,872KHz. + */ static unsigned int marvell_i2c_bus_speed_set(unsigned int requested_speed) { unsigned int n, m, freq, margin, min_margin = 0xffffffff; |