[PATCH] MMC:mmc_spi: Recover from CRC error for SD read/write operation over SPI.

[sonic zhang <sonic.adi@gmail.com>]

>From 94d1ea57ac2fbe37133e25e99ccb265250f0027d Mon Sep 17 00:00:00 2001
From: Sonic Zhang <sonic.zhang@analog.com>
Date: Fri, 9 Jul 2010 15:36:20 +0800
Subject: [PATCH] MMC:mmc_spi: Recover from CRC error for SD read/write operation over SPI.

SPI bus is not reliable on all platforms when doing large dada transfer.
Current mmc spi driver fails SD read/write command immediately, if
occational CRC error is reported by SD device. This patch makes the
operation recover from the CRC error by doing last SD command again.
The retry count is set to 5 to ensure the driver pass any stress test.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
---
 drivers/mmc/host/mmc_spi.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index ad847a2..8192434 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1055,6 +1055,8 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
 {
 	struct mmc_spi_host	*host = mmc_priv(mmc);
 	int			status = -EINVAL;
+	int			crc_retry = 5;
+	struct mmc_command	stop;
 
 #ifdef DEBUG
 	/* MMC core and layered drivers *MUST* issue SPI-aware commands */
@@ -1084,10 +1086,30 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
 	}
 #endif
 
+crc_recover:
 	/* issue command; then optionally data and stop */
 	status = mmc_spi_command_send(host, mrq, mrq->cmd, mrq->data != NULL);
 	if (status == 0 && mrq->data) {
 		mmc_spi_data_do(host, mrq->cmd, mrq->data, mrq->data->blksz);
+ 
+ 		/*
+ 		 * SPI bus is not reliable when doing large dada transfer.
+ 		 * If occational crc error is reported by SD device when do
+ 		 * data read/write over SPI, it can be recovered by doing
+ 		 * last SD command again. The retry count is set to 5 to
+ 		 * ensure the driver pass any stress test.
+ 		 */
+ 		if (mrq->data->error == -EILSEQ && crc_retry) {
+ 			stop.opcode = MMC_STOP_TRANSMISSION;
+ 			stop.arg = 0;
+ 			stop.flags = MMC_RSP_SPI_R1B | MMC_RSP_R1B | MMC_CMD_AC;
+ 
+ 			status = mmc_spi_command_send(host, mrq, &stop, 0);
+ 			crc_retry--;
+ 			mrq->data->error = 0;
+ 			goto crc_recover;
+ 		}
+ 
 		if (mrq->stop)
 			status = mmc_spi_command_send(host, mrq, mrq->stop, 0);
 		else
-- 
1.6.0