Re: [U-Boot] [PATCH v2] spi: mxc_spi: Update pre and post divider algorithm

Hi Dirk,

On 12/06/2013 07:28, Dirk Behme wrote:

On 11.05.2013 07:25, Dirk Behme wrote:

...

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

While we are talking about a first -rc now, could we get these two patches

http://patchwork.ozlabs.org/patch/242709/

http://patchwork.ozlabs.org/patch/243113/

Sorry to come late with these two patches - after a first glance when you post then, I put the patches at the bottom of my queue and I never checked again.

I will work them before end of the week.

Best regards, Stefano Babic

applied?

Thanks

Dirk

...

---

Notes:

• Changes in v2: Make the alogrithm simpler by removing the -1 as

proposed by Troy. Make the pre_div and post_div u32.

• This replaces v1 of this patch and depends on the previous sent patch http://patchwork.ozlabs.org/patch/242709/

  drivers/spi/mxc_spi.c | 30 ++++++++++++------------------ 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c index 3e903b3..e87b899 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(&regs->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);