This patch makes SDHC cards work with the mmc_spi driver.

The problem is that they fail when reading the last block of the card using
a multi-block read. This is because on SDHC the multiple block read has to be
stopped with an explicit STOP command, which needs to be sent to the card
while the incoming transfer is in progress.
The 2.6.3[45] mmc-spi driver sends it after the last block transfer, so the
SDHC card continues reading past the end of the card.
This patch works around this by using single-block reads if we're reading the
last blocks of the card.
  -martinwguy, 14 May 2010

Date: Thu, 29 Apr 2010 21:30:36 +0300
From: Mika Westerberg <mika.westerberg@iki.fi>
To: Martin Guy <martinwguy@gmail.com>

On Wed, Apr 21, 2010 at 02:10:08AM +0100, Martin Guy wrote:
> 
> the SDHC cards I have don't work at all, spewing tons of:
> mmcblk0: error -38 sending status comand
> mmcblk0: error -38 sending read/write command, response 0x4, card status 0xff04
> end_request: I/O error, dev mmcblk0, sector 7744509

I bought today a new 4GB SDHC card and with that I get similar
errors that you are getting. I hacked around quick fix which seems
to work in my case. I'm wondering whether you could check if it
helps with your SDHC card as well?

This problem is easy to reproduce, just read last sector of the
card (I wrote simple C program but running fdisk -l does the same).

Patch is below.

Thanks,
MW

From: Mika Westerberg <mika.westerberg@iki.fi>
Date: Thu, 29 Apr 2010 21:14:32 +0300
Subject: [PATCH] mmc_block: use single block reads for last block on SPI

Some SD-cards fail when doing multiblock read for last block with SPI host. Real
reason is not known but as workaround we can perform this last read using
multiple single block reads.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
---
 drivers/mmc/card/block.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -351,6 +351,22 @@ static int mmc_blk_issue_rw_rq(struct mm
 		if (brq.data.blocks > card->host->max_blk_count)
 			brq.data.blocks = card->host->max_blk_count;
 
+		if (mmc_host_is_spi(card->host)) {
+			/*
+			 * Some SD-cards fail when we are reading last block
+			 * with multiblock read. In these cases we automatically
+			 * use single block reads. This only happens on SPI
+			 * hosts.
+			 */
+			if (rq_data_dir(req) == READ && brq.data.blocks > 1) {
+				sector_t s = blk_rq_pos(req) + brq.data.blocks;
+
+				if (s >= get_capacity(md->disk)) {
+					disable_multi = 1;
+				}
+			}
+		}
+
 		/*
 		 * After a read error, we redo the request one sector at a time
 		 * in order to accurately determine which sectors can be read
