The spi clock divisor is of the form x * (2**y), or x << y, where x is 1 to 16, and y is 0 to 15. Note the similarity with floating point numbers. Convert the desired divisor to the smallest number which is >= desired divisor, and can be represented in this form. The previous algorithm chose a divisor which could be almost twice as large as needed.
Signed-off-by: Troy Kisky <troy.ki...@boundarydevices.com> Signed-off-by: Dirk Behme <dirk.be...@gmail.com> --- drivers/spi/mxc_spi.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c index 3e903b3..66c2ad8 100644 --- a/drivers/spi/mxc_spi.c +++ b/drivers/spi/mxc_spi.c @@ -128,7 +128,7 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs, unsigned int max_hz, unsigned int mode) { u32 clk_src = mxc_get_clock(MXC_CSPI_CLK); - s32 pre_div = 1, post_div = 0, i, reg_ctrl, reg_config; + s32 pre_div = 1, post_div = 0, reg_ctrl, reg_config; u32 ss_pol = 0, sclkpol = 0, sclkpha = 0; struct cspi_regs *regs = (struct cspi_regs *)mxcs->base; @@ -147,27 +147,24 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs, reg_ctrl |= MXC_CSPICTRL_EN; reg_write(®s->ctrl, reg_ctrl); - /* - * The following computation is taken directly from Freescale's code. - */ if (clk_src > max_hz) { pre_div = DIV_ROUND_UP(clk_src, max_hz); - if (pre_div > 16) { - post_div = pre_div / 16; - pre_div = 16; - } - if (post_div != 0) { - for (i = 0; i < 16; i++) { - if ((1 << i) >= post_div) - break; - } - if (i == 16) { + /* fls(1) = 1, fls(0x80000000) = 32, fls(16) = 5 */ + post_div = fls(pre_div - 1); + if (post_div > 4) { + post_div -= 4; + + if (post_div >= 16) { printf("Error: no divider for the freq: %d\n", max_hz); return -1; } - post_div = i; + pre_div = (pre_div + (1 << post_div) - 1) >> post_div; + + } else { + post_div = 0; } + } debug("pre_div = %d, post_div=%d\n", pre_div, post_div); -- 1.7.10.4 _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot