[PATCH 4/7 revised] mmc_spi: do not check CID and CSD blocks with CRC16

From: Wolfgang Mües
Date: Wed Mar 18 2009 - 05:53:11 EST


From: Wolfgang Muees <wolfgang.mues@xxxxxxxxxxxx>

o Some cards are not able to calculate a valid CRC16 value
for CID and CSD reads (CRC for 512 byte data blocks is OK).
So ommit the check for CRC16, as CID and CSD have a checksum
inside the block.

Signed-off-by: Wolfgang Muees <wolfgang.mues@xxxxxxxxxxxx>

---

This is patch #4 revised to apply after #1,#2,#5 (already applied)
and #3 (acked by David Brownell). Documentation was extended.
There were some suggestions to move this check into an upper layer
but none of these tries were a valid solution, so stick with this
minimal change here in the readblock function.

diff -uprN 2_6_29_rc7_patch1253/drivers/mmc/host/mmc_spi.c 2_6_29_rc7_patch12534/drivers/mmc/host/mmc_spi.c
--- 2_6_29_rc7_patch1253/drivers/mmc/host/mmc_spi.c 2009-03-16 12:15:36.000000000 +0100
+++ 2_6_29_rc7_patch12534/drivers/mmc/host/mmc_spi.c 2009-03-18 10:32:45.000000000 +0100
@@ -767,7 +767,13 @@ mmc_spi_readblock(struct mmc_spi_host *h
return -EIO;
}

- if (host->mmc->use_spi_crc) {
+ /* Omitt the CRC check for CID reads. There are some SDHC
+ * cards which don't supply a valid CRC after CID reads.
+ * All data reads have len == MMC_SPI_BLOCKSIZE, so use this
+ * check to distinguish between data reads and CID/CSD reads.
+ * Note that CID/CSD has it's own CRC7 value inside the structure.
+ */
+ if (host->mmc->use_spi_crc && (t->len == MMC_SPI_BLOCKSIZE)) {
u16 crc = crc_itu_t(0, t->rx_buf, t->len);

be16_to_cpus(&scratch->crc_val);

---
regards

i. A. Wolfgang Mües
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