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

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

[Wolfgang Mües]

From: Wolfgang Muees <wolfgang.mues@auerswald.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@auerswald.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
-- 
Auerswald GmbH & Co. KG
Hardware Development
Telefon: +49 (0)5306 9219 0
Telefax: +49 (0)5306 9219 94 
E-Mail: Wolfgang.Mues@Auerswald.de
Web: http://www.auerswald.de
 
--------------------------------------------------------------
Auerswald GmbH & Co. KG, Vor den Grashöfen 1, 38162 Cremlingen
Registriert beim AG Braunschweig HRA 13289
p.h.G Auerswald Geschäftsführungsges. mbH
Registriert beim AG Braunschweig HRB 7463
Geschäftsführer: Dipl-Ing. Gerhard Auerswald

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

[David Brownell]

On Wednesday 18 March 2009, Wolfgang Mües wrote:
> From: Wolfgang Muees <wolfgang.mues@auerswald.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@auerswald.de>

Acked-by: David Brownell <dbrownell@users.sourceforge.net>

.... though I'd edit the patch to spell "Omit" with just one "t".

> 
> ---
> 
> 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
> -- 
> Auerswald GmbH & Co. KG
> Hardware Development
> Telefon: +49 (0)5306 9219 0
> Telefax: +49 (0)5306 9219 94 
> E-Mail: Wolfgang.Mues@Auerswald.de
> Web: http://www.auerswald.de
>  
> --------------------------------------------------------------
> Auerswald GmbH & Co. KG, Vor den Grashöfen 1, 38162 Cremlingen
> Registriert beim AG Braunschweig HRA 13289
> p.h.G Auerswald Geschäftsführungsges. mbH
> Registriert beim AG Braunschweig HRB 7463
> Geschäftsführer: Dipl-Ing. Gerhard Auerswald
> 
>