fsl_esdhc: Correcting esdhc timeout counter calculation

[pandora-u-boot.git] / drivers / mmc / fsl_esdhc.c

diff --git a/drivers/mmc/fsl_esdhc.c b/drivers/mmc/fsl_esdhc.c
index f3cccbe..0962ac4 100644 (file)
--- 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(&regs->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)