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>
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 @@
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