From: Bin Meng bin.meng@windriver.com
After command is sent and before card response shows up on the line, there is a variable number of clock cycles in between called Ncr. The spec [1] says the minimum is 1 byte and the maximum is 8 bytes.
Current logic in mmc_spi_sendcmd() has a flaw that it could only work with certain SD cards with their Ncr being just 1 byte.
When resp_match is false, the codes try to receive only 1 byte from the SD card. On the other hand when resp_match is true, the logic happens to be no problem as it loops until timeout to receive as many bytes as possible to see a match of the expected resp_match_value. However not every call to mmc_spi_sendcmd() is made with resp_match being true hence this exposes a potential issue with SD cards that have a larger Ncr value.
Given no issue was reported as of today, we can reasonably conclude that all cards being used on the supported boards happen to have a 1 byte Ncr timing requirement. But a broken case can be triggered by utilizing QEMU to emulate a larger value of Ncr (by default 1 byte Ncr is used on QEMU). This commit fixes such potential spec violation to improve the card compatibility.
[1] "Physical Layer Specification Version 8.00" chapter 7.5.1: Command / Response chapter 7.5.4: Timing Values
Signed-off-by: Bin Meng bin.meng@windriver.com Reviewed-by: Jaehoon Chung jh80.chung@samsung.com ---
(no changes since v1)
drivers/mmc/mmc_spi.c | 32 +++++++++++++++++--------------- 1 file changed, 17 insertions(+), 15 deletions(-)
diff --git a/drivers/mmc/mmc_spi.c b/drivers/mmc/mmc_spi.c index a06862a..fbdbcf7 100644 --- a/drivers/mmc/mmc_spi.c +++ b/drivers/mmc/mmc_spi.c @@ -103,29 +103,31 @@ static int mmc_spi_sendcmd(struct udevice *dev,
debug("%s: cmd%d", __func__, cmdidx);
- if (resp_match) { + if (resp_match) r = ~resp_match_value; - i = CMD_TIMEOUT; - while (i) { - ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0); - if (ret) - return ret; - debug(" resp%d=0x%x", rpos, r); - rpos++; - i--; + i = CMD_TIMEOUT; + while (i) { + ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0); + if (ret) + return ret; + debug(" resp%d=0x%x", rpos, r); + rpos++; + i--;
+ if (resp_match) { if (r == resp_match_value) break; + } else { + if (!(r & 0x80)) + break; } - if (!i && (r != resp_match_value)) + + if (!i) return -ETIMEDOUT; }
- for (i = 0; i < resp_size; i++) { - if (i == 0 && resp_match) { - resp[i] = resp_match_value; - continue; - } + resp[0] = r; + for (i = 1; i < resp_size; i++) { ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0); if (ret) return ret;