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

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Message-Id: <200903241311.02878.david-b@pacbell.net>
Date:	Tue, 24 Mar 2009 13:11:02 -0700
From:	David Brownell <david-b@...bell.net>
To:	Wolfgang Mües <wolfgang.mues@...rswald.de>
Cc:	Pierre Ossman <drzeus@...eus.cx>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Matt Fleming" <matt@...sole-pimps.org>,
	"Mike Frysinger" <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7 revised] mmc_spi: do not check CID and CSD blocks with CRC16

On Wednesday 18 March 2009, Wolfgang Mües wrote:
> 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>

Acked-by: David Brownell <dbrownell@...rs.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
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> E-Mail: Wolfgang.Mues@...rswald.de
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>  
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