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mmc: mmc_spi: Fix potential spec violation in receiving card response
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>
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parent
781aad0de9
commit
2f22cb40e5
@ -103,29 +103,31 @@ static int mmc_spi_sendcmd(struct udevice *dev,
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debug("%s: cmd%d", __func__, cmdidx);
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debug("%s: cmd%d", __func__, cmdidx);
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if (resp_match) {
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if (resp_match)
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r = ~resp_match_value;
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r = ~resp_match_value;
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i = CMD_TIMEOUT;
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i = CMD_TIMEOUT;
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while (i) {
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while (i) {
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ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0);
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ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0);
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if (ret)
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if (ret)
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return ret;
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return ret;
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debug(" resp%d=0x%x", rpos, r);
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debug(" resp%d=0x%x", rpos, r);
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rpos++;
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rpos++;
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i--;
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i--;
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if (resp_match) {
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if (r == resp_match_value)
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if (r == resp_match_value)
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break;
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break;
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} else {
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if (!(r & 0x80))
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break;
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}
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}
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if (!i && (r != resp_match_value))
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if (!i)
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return -ETIMEDOUT;
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return -ETIMEDOUT;
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}
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}
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for (i = 0; i < resp_size; i++) {
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resp[0] = r;
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if (i == 0 && resp_match) {
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for (i = 1; i < resp_size; i++) {
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resp[i] = resp_match_value;
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continue;
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}
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ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0);
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ret = dm_spi_xfer(dev, 1 * 8, NULL, &r, 0);
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if (ret)
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if (ret)
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return ret;
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return ret;
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