mmc,sdio: helper function for transfer padding

There are a lot of crappy controllers out there that cannot handle
all the request sizes that the MMC/SD/SDIO specifications require.
In case the card driver can pad the data to overcome the problems,
this commit adds a helper that calculates how much that padding
should be.

A corresponding helper is also added for SDIO, but it can also deal
with all the complexities of splitting up a large transfer efficiently.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

2 files changed, 126 insertions, 2 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index ede5d1e..3ee5b8c 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -3,7 +3,7 @@
  *
  *  Copyright (C) 2003-2004 Russell King, All Rights Reserved.
  *  SD support Copyright (C) 2004 Ian Molton, All Rights Reserved.
- *  Copyright (C) 2005-2007 Pierre Ossman, All Rights Reserved.
+ *  Copyright (C) 2005-2008 Pierre Ossman, All Rights Reserved.
  *  MMCv4 support Copyright (C) 2006 Philip Langdale, All Rights Reserved.
  *
  * This program is free software; you can redistribute it and/or modify
@@ -295,6 +295,33 @@ void mmc_set_data_timeout(struct mmc_data *data, const struct mmc_card *card)
 EXPORT_SYMBOL(mmc_set_data_timeout);
 
 /**
+ *	mmc_align_data_size - pads a transfer size to a more optimal value
+ *	@card: the MMC card associated with the data transfer
+ *	@sz: original transfer size
+ *
+ *	Pads the original data size with a number of extra bytes in
+ *	order to avoid controller bugs and/or performance hits
+ *	(e.g. some controllers revert to PIO for certain sizes).
+ *
+ *	Returns the improved size, which might be unmodified.
+ *
+ *	Note that this function is only relevant when issuing a
+ *	single scatter gather entry.
+ */
+unsigned int mmc_align_data_size(struct mmc_card *card, unsigned int sz)
+{
+	/*
+	 * FIXME: We don't have a system for the controller to tell
+	 * the core about its problems yet, so for now we just 32-bit
+	 * align the size.
+	 */
+	sz = ((sz + 3) / 4) * 4;
+
+	return sz;
+}
+EXPORT_SYMBOL(mmc_align_data_size);
+
+/**
  *	__mmc_claim_host - exclusively claim a host
  *	@host: mmc host to claim
  *	@abort: whether or not the operation should be aborted
diff --git a/drivers/mmc/core/sdio_io.c b/drivers/mmc/core/sdio_io.c
index 625b92c..6ee7861 100644
--- a/drivers/mmc/core/sdio_io.c
+++ b/drivers/mmc/core/sdio_io.c
@@ -1,7 +1,7 @@
 /*
  *  linux/drivers/mmc/core/sdio_io.c
  *
- *  Copyright 2007 Pierre Ossman
+ *  Copyright 2007-2008 Pierre Ossman
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -189,6 +189,103 @@ int sdio_set_block_size(struct sdio_func *func, unsigned blksz)
 
 EXPORT_SYMBOL_GPL(sdio_set_block_size);
 
+/**
+ *	sdio_align_size - pads a transfer size to a more optimal value
+ *	@func: SDIO function
+ *	@sz: original transfer size
+ *
+ *	Pads the original data size with a number of extra bytes in
+ *	order to avoid controller bugs and/or performance hits
+ *	(e.g. some controllers revert to PIO for certain sizes).
+ *
+ *	If possible, it will also adjust the size so that it can be
+ *	handled in just a single request.
+ *
+ *	Returns the improved size, which might be unmodified.
+ */
+unsigned int sdio_align_size(struct sdio_func *func, unsigned int sz)
+{
+	unsigned int orig_sz;
+	unsigned int blk_sz, byte_sz;
+	unsigned chunk_sz;
+
+	orig_sz = sz;
+
+	/*
+	 * Do a first check with the controller, in case it
+	 * wants to increase the size up to a point where it
+	 * might need more than one block.
+	 */
+	sz = mmc_align_data_size(func->card, sz);
+
+	/*
+	 * If we can still do this with just a byte transfer, then
+	 * we're done.
+	 */
+	if ((sz <= func->cur_blksize) && (sz <= 512))
+		return sz;
+
+	if (func->card->cccr.multi_block) {
+		/*
+		 * Check if the transfer is already block aligned
+		 */
+		if ((sz % func->cur_blksize) == 0)
+			return sz;
+
+		/*
+		 * Realign it so that it can be done with one request,
+		 * and recheck if the controller still likes it.
+		 */
+		blk_sz = ((sz + func->cur_blksize - 1) /
+			func->cur_blksize) * func->cur_blksize;
+		blk_sz = mmc_align_data_size(func->card, blk_sz);
+
+		/*
+		 * This value is only good if it is still just
+		 * one request.
+		 */
+		if ((blk_sz % func->cur_blksize) == 0)
+			return blk_sz;
+
+		/*
+		 * We failed to do one request, but at least try to
+		 * pad the remainder properly.
+		 */
+		byte_sz = mmc_align_data_size(func->card,
+				sz % func->cur_blksize);
+		if ((byte_sz <= func->cur_blksize) && (byte_sz <= 512)) {
+			blk_sz = sz / func->cur_blksize;
+			return blk_sz * func->cur_blksize + byte_sz;
+		}
+	} else {
+		/*
+		 * We need multiple requests, so first check that the
+		 * controller can handle the chunk size;
+		 */
+		chunk_sz = mmc_align_data_size(func->card,
+				min(func->cur_blksize, 512u));
+		if (chunk_sz == min(func->cur_blksize, 512u)) {
+			/*
+			 * Fix up the size of the remainder (if any)
+			 */
+			byte_sz = orig_sz % chunk_sz;
+			if (byte_sz) {
+				byte_sz = mmc_align_data_size(func->card,
+						byte_sz);
+			}
+
+			return (orig_sz / chunk_sz) * chunk_sz + byte_sz;
+		}
+	}
+
+	/*
+	 * The controller is simply incapable of transferring the size
+	 * we want in decent manner, so just return the original size.
+	 */
+	return orig_sz;
+}
+EXPORT_SYMBOL_GPL(sdio_align_size);
+
 /* Split an arbitrarily sized data transfer into several
  * IO_RW_EXTENDED commands. */
 static int sdio_io_rw_ext_helper(struct sdio_func *func, int write,