diff options
Diffstat (limited to 'drivers/mmc/fsl_esdhc.c')
| -rw-r--r-- | drivers/mmc/fsl_esdhc.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/mmc/fsl_esdhc.c b/drivers/mmc/fsl_esdhc.c index f3cccbe9bf..0962ac4476 100644 --- a/drivers/mmc/fsl_esdhc.c +++ b/drivers/mmc/fsl_esdhc.c @@ -210,7 +210,21 @@ 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 = fls(mmc->tran_speed/10) - 1; + /* + * 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; if (timeout > 14) |