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authorPriyanka Jain <Priyanka.Jain@freescale.com>2011-03-03 09:18:56 +0530
committerKumar Gala <galak@kernel.crashing.org>2011-03-07 08:49:28 -0600
commitb71ea33699bb694964929e2cdced80ef794bde69 (patch)
treeaadaa4c2e5edd0b040c629286fdf16636c736f9d /drivers
parent509e19cab43ba38311749eba5ceebd806116ce38 (diff)
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fsl_esdhc: Correcting esdhc timeout counter calculation
- 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> Acked-by: Mingkai Hu <Mingkai.Hu@freescale.com> Tested-by: Stefano Babic <sbabic@denx.de> Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/mmc/fsl_esdhc.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/mmc/fsl_esdhc.c b/drivers/mmc/fsl_esdhc.c
index f3cccbe..0962ac4 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(&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)