linux-kernel - Re: [PATCH 3/7 revised] mmc_spi: adjust for delayed data token response

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Date:	Mon, 16 Mar 2009 12:37:36 -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 3/7 revised] mmc_spi: adjust for delayed data token response

On Monday 16 March 2009, Wolfgang Mües wrote:
> From: Wolfgang Muees <wolfgang.mues@...rswald.de>
> 
> o some cards are not able to send the data token in time, but
>   miss the time frame for some bits(!). So synchronize to the
>   start of the token.
> 
> Signed-off-by: Wolfgang Muees <wolfgang.mues@...rswald.de>

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


> ---
> 
> This is the revised patch #3, to apply after the already accepted 
> patches #1,2 and #5. It contains the bugfix and a better explanation
> of what is going on here.
> 
> diff -uprN 2_6_29_rc7_patch125/drivers/mmc/host/mmc_spi.c 2_6_29_rc7_patch1253/drivers/mmc/host/mmc_spi.c
> --- 2_6_29_rc7_patch125/drivers/mmc/host/mmc_spi.c	2009-03-11 13:00:06.000000000 +0100
> +++ 2_6_29_rc7_patch1253/drivers/mmc/host/mmc_spi.c	2009-03-16 12:15:36.000000000 +0100
> @@ -612,6 +612,7 @@ mmc_spi_writeblock(struct mmc_spi_host *
>  	struct spi_device	*spi = host->spi;
>  	int			status, i;
>  	struct scratch		*scratch = host->data;
> +	u32			pattern;
>  
>  	if (host->mmc->use_spi_crc)
>  		scratch->crc_val = cpu_to_be16(
> @@ -639,8 +640,27 @@ mmc_spi_writeblock(struct mmc_spi_host *
>  	 * doesn't necessarily tell whether the write operation succeeded;
>  	 * it just says if the transmission was ok and whether *earlier*
>  	 * writes succeeded; see the standard.
> -	 */
> -	switch (SPI_MMC_RESPONSE_CODE(scratch->status[0])) {
> +	 *
> +	 * In practice, there are (even modern SDHC-)cards which are late
> +	 * in sending the response, and miss the time frame by a few bits,
> +	 * so we have to cope with this situation and check the response 
> +	 * bit-by-bit. Arggh!!!
> +	 */
> +	pattern  = scratch->status[0] << 24;
> +	pattern |= scratch->status[1] << 16;
> +	pattern |= scratch->status[2] << 8;
> +	pattern |= scratch->status[3];
> +
> +	/* First 3 bit of pattern are undefined */
> +	pattern |= 0xE0000000;
> +
> +	/* left-adjust to leading 0 bit */
> +	while (pattern & 0x80000000)
> +		pattern <<= 1;
> +	/* right-adjust for pattern matching. Code is in bit 4..0 now. */
> +	pattern >>= 27;
> +
> +	switch (pattern) {
>  	case SPI_RESPONSE_ACCEPTED:
>  		status = 0;
>  		break;
> @@ -671,8 +691,9 @@ mmc_spi_writeblock(struct mmc_spi_host *
>  	/* Return when not busy.  If we didn't collect that status yet,
>  	 * we'll need some more I/O.
>  	 */
> -	for (i = 1; i < sizeof(scratch->status); i++) {
> -		if (scratch->status[i] != 0)
> +	for (i = 4; i < sizeof(scratch->status); i++) {
> +		/* card is non-busy if the most recent bit is 1 */
> +		if (scratch->status[i] & 0x01)
>  			return 0;
>  	}
>  	return mmc_spi_wait_unbusy(host, timeout);
> 
> ---
> 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@...rswald.de
> Web: http://www.auerswald.de
>  
> --------------------------------------------------------------
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