diff options
| author | Dirk Behme <dirk.behme@gmail.com> | 2013-05-11 07:25:54 +0200 |
|---|---|---|
| committer | Stefano Babic <sbabic@denx.de> | 2013-06-26 16:23:30 +0200 |
| commit | 9a30903b44a63861de93d5beaaf4c91173bbac0c (patch) | |
| tree | 5a4af903597414caf5d8f62d7725a32858709e78 /drivers | |
| parent | 8d4c4ffb95d528f6a709bf68da5e0beb0f4ee72f (diff) | |
spi: mxc_spi: Update pre and post divider algorithm
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.kisky@boundarydevices.com>
Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/spi/mxc_spi.c | 30 |
1 files changed, 12 insertions, 18 deletions
diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c index b553a9c5965..0eca7767e0b 100644 --- a/drivers/spi/mxc_spi.c +++ b/drivers/spi/mxc_spi.c @@ -128,8 +128,8 @@ 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; - u32 ss_pol = 0, sclkpol = 0, sclkpha = 0; + s32 reg_ctrl, reg_config; + u32 ss_pol = 0, sclkpol = 0, sclkpha = 0, pre_div = 0, post_div = 0; struct cspi_regs *regs = (struct cspi_regs *)mxcs->base; if (max_hz == 0) { @@ -147,26 +147,20 @@ 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) { + pre_div = (clk_src - 1) / max_hz; + /* fls(1) = 1, fls(0x80000000) = 32, fls(16) = 5 */ + post_div = fls(pre_div); + 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 >>= post_div; + } else { + post_div = 0; } } @@ -174,7 +168,7 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs, reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_SELCHAN(3)) | MXC_CSPICTRL_SELCHAN(cs); reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_PREDIV(0x0F)) | - MXC_CSPICTRL_PREDIV(pre_div - 1); + MXC_CSPICTRL_PREDIV(pre_div); reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_POSTDIV(0x0F)) | MXC_CSPICTRL_POSTDIV(post_div); |