- Timeout counter value is set as DTOCV bits in SYSCTL register For counter value set as timeout, Timeout period = (2^(timeout + 13)) SD Clock cycles
- As per 4.6.2.2 section of SD Card specification v2.00, host should cofigure timeout period value to minimum 0.25 sec.
- Number of SD Clock cycles for 0.25sec should be minimum (SD Clock/sec * 0.25 sec) SD Clock cycles = (mmc->tran_speed * 1/4) SD Clock cycles
- Calculating timeout based on (2^(timeout + 13)) >= mmc->tran_speed * 1/4 Taking log2 both the sides and rounding up to next power of 2 => timeout + 13 = log2(mmc->tran_speed/4) + 1
Signed-off-by: Priyanka Jain Priyanka.Jain@freescale.com Signed-off-by: Andy Fleming afleming@freescale.com Signed-off-by: Kumar Gala galak@kernel.crashing.org Acked-by: Mingkai Hu Mingkai.Hu@freescale.com --- Changes for v2: Added proper description as suggested by Wolfgang Denk
drivers/mmc/fsl_esdhc.c | 15 +++++++++++++-- 1 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/drivers/mmc/fsl_esdhc.c b/drivers/mmc/fsl_esdhc.c index 9c69cc7..e8dd9b7 100644 --- a/drivers/mmc/fsl_esdhc.c +++ b/drivers/mmc/fsl_esdhc.c @@ -207,8 +207,19 @@ static int esdhc_setup_data(struct mmc *mmc, struct mmc_data *data) esdhc_write32(®s->blkattr, data->blocks << 16 | data->blocksize);
/* Calculate the timeout period for data transactions */ - /* Timeout period = (2^(13+timeout))/mmc->trans_speed - * Timeout period should be minimum 250msec as per SD Card spec + /* + * 1)Timeout period = (2^(timeout+13)) SD Clock cycles + * 2)Timeout period should be minimum 0.250sec as per SD Card spec + * So, Number of SD Clock cycles for 0.25sec should be minimum + * (SD Clock/sec * 0.25 sec) SD Clock cycles + * = (mmc->tran_speed * 1/4) SD Clock cycles + * As 1) >= 2) + * => (2^(timeout+13)) >= mmc->tran_speed * 1/4 + * Taking log2 both the sides + * => timeout + 13 >= log2(mmc->tran_speed/4) + * Rounding up to next power of 2 + * => timeout + 13 = log2(mmc->tran_speed/4) + 1 + * => timeout + 13 = fls(mmc->tran_speed/4) */ timeout = fls(mmc->tran_speed/4); timeout -= 13;