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

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Message-Id: <200903111425.48656.wolfgang.mues@auerswald.de>
Date:	Wed, 11 Mar 2009 14:25:48 +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] 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 one of a line of patches to enhance the usability of
the mmc spi host port driver from "don't work with most SD cards"
to "work with nearly all SD cards" (including those ugly cards
with non-byte-aligned responses).

diff -uprN 2_6_29_rc7_patch3_delayed_data_response/drivers/mmc/host/mmc_spi.c 2_6_29_rc7_patch4_no_crc_on_CID_CSD/drivers/mmc/host/mmc_spi.c
--- 2_6_29_rc7_patch3_delayed_data_response/drivers/mmc/host/mmc_spi.c	2009-03-11 13:42:48.000000000 +0100
+++ 2_6_29_rc7_patch4_no_crc_on_CID_CSD/drivers/mmc/host/mmc_spi.c	2009-03-11 13:43:13.000000000 +0100
@@ -762,7 +762,11 @@ mmc_spi_readblock(struct mmc_spi_host *h
 		return -EIO;
 	}
 
-	if (host->mmc->use_spi_crc) {
+	/* Omitt the CRC check for CID and CSD reads. There are some SDHC
+	 * cards which don't supply a valid CRC after CID reads.
+	 * Note that the CID has it's own CRC7 value inside the data block.
+	 */
+	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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