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

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Date:	Wed, 18 Mar 2009 10:52:39 +0100
From:	Wolfgang Mües <wolfgang.mues@...rswald.de>
To:	Pierre Ossman <drzeus@...eus.cx>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Matt Fleming" <matt@...sole-pimps.org>,
	"David Brownell" <dbrownell@...rs.sourceforge.net>,
	"Mike Frysinger" <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/7 revised] mmc_spi: do not check CID and CSD blocks with CRC16

From: Wolfgang Muees <wolfgang.mues@...rswald.de>

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@...rswald.de>

---

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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