- 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.j...@freescale.com>
Signed-off-by: Andy Fleming <aflem...@freescale.com>
Signed-off-by: Kumar Gala <ga...@kernel.crashing.org>
Acked-by: Mingkai Hu <mingkai...@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;
--
1.6.5.6
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