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mmc: fsl_esdhc: fix calculation of timeout for data transactions

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Calculation of the timeout value should be based on actual clock value,
written to controller registers. Since mmc->tran_speed is either the
maximum allowed speed, or the preliminary value, that is be not yet
set to registers, the actual timeout, taken by the controller, based
on its clock settings, may be much longer than expected, based on
mmc->tran_speed value. In particular it happens at early initialization
stage, when typical value of mmc->tran_speed is 20MHz or 26MHz, while
actual clock setting, configured in the controller, is 400kHz.
It's more correct to use mmc->clock value for timeout calculation instead.

Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>
This commit is contained in:
Andrew Gabbasov 2014-03-24 02:40:41 -05:00 committed by Pantelis Antoniou
parent 33ace362fd
commit fb823981c5
1 changed files with 6 additions and 6 deletions
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12
drivers/mmc/fsl_esdhc.c
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@ -221,16 +221,16 @@ static int esdhc_setup_data(struct mmc *mmc, struct mmc_data *data)
* 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
* = (mmc->clock * 1/4) SD Clock cycles
* As 1) >= 2)
* => (2^(timeout+13)) >= mmc->tran_speed * 1/4
* => (2^(timeout+13)) >= mmc->clock * 1/4
* Taking log2 both the sides
* => timeout + 13 >= log2(mmc->tran_speed/4)
* => timeout + 13 >= log2(mmc->clock/4)
* Rounding up to next power of 2
* => timeout + 13 = log2(mmc->tran_speed/4) + 1
* => timeout + 13 = fls(mmc->tran_speed/4)
* => timeout + 13 = log2(mmc->clock/4) + 1
* => timeout + 13 = fls(mmc->clock/4)
*/
timeout = fls(mmc->tran_speed/4);
timeout = fls(mmc->clock/4);
timeout -= 13;
if (timeout > 14)