[PATCH v3] mtd: nand: Add support to use nand_base poi databuf as bounce buffer

[Kamal Dasu]

nand_base can be passed a kmap()'d buffers from highmem by
filesystems like jffs2. This results in failure to map the
physical address of the DMA buffer on various contoller
driver on different platforms. This change adds a chip option
to use preallocated databuf as bounce buffers used in
nand_do_read_ops() and nand_do_write_ops().
This allows for specific nand controller driver to set this
option as needed.

Signed-off-by: Kamal Dasu <kdasu.kdev at gmail.com>
---

Changes since v2:
 * fix ARM build by including linux/mm.h
 * print highmem buffer address in pr_debug

 drivers/mtd/nand/nand_base.c | 31 ++++++++++++++++++++++++-------
 include/linux/mtd/nand.h     |  5 +++++
 2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 9d01c4d..27505cd 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -37,6 +37,7 @@
 #include <linux/err.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include <linux/types.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/nand.h>
@@ -1501,6 +1502,7 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 		mtd->oobavail : mtd->oobsize;
 
 	uint8_t *bufpoi, *oob, *buf;
+	int use_bufpoi;
 	unsigned int max_bitflips = 0;
 	int retry_mode = 0;
 	bool ecc_fail = false;
@@ -1522,10 +1524,17 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
 
 		bytes = min(mtd->writesize - col, readlen);
 		aligned = (bytes == mtd->writesize);
+		use_bufpoi = (chip->options & NAND_USE_BOUNCE_BUFFER) ?
+				!virt_addr_valid(buf) : 0;
 
 		/* Is the current page in the buffer? */
 		if (realpage != chip->pagebuf || oob) {
-			bufpoi = aligned ? buf : chip->buffers->databuf;
+			bufpoi = (aligned && !use_bufpoi) ? buf :
+				chip->buffers->databuf;
+
+			if (use_bufpoi && aligned)
+				pr_debug("%s: using bounce buffer for buf@%p\n",
+						 __func__, bufpoi);
 
 read_retry:
 			chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
@@ -1547,7 +1556,7 @@ read_retry:
 				ret = chip->ecc.read_page(mtd, chip, bufpoi,
 							  oob_required, page);
 			if (ret < 0) {
-				if (!aligned)
+				if (!aligned || use_bufpoi)
 					/* Invalidate page cache */
 					chip->pagebuf = -1;
 				break;
@@ -1556,7 +1565,7 @@ read_retry:
 			max_bitflips = max_t(unsigned int, max_bitflips, ret);
 
 			/* Transfer not aligned data */
-			if (!aligned) {
+			if (!aligned || use_bufpoi) {
 				if (!NAND_HAS_SUBPAGE_READ(chip) && !oob &&
 				    !(mtd->ecc_stats.failed - ecc_failures) &&
 				    (ops->mode != MTD_OPS_RAW)) {
@@ -2376,11 +2385,19 @@ static int nand_do_write_ops(struct mtd_info *mtd, loff_t to,
 		int bytes = mtd->writesize;
 		int cached = writelen > bytes && page != blockmask;
 		uint8_t *wbuf = buf;
-
-		/* Partial page write? */
-		if (unlikely(column || writelen < (mtd->writesize - 1))) {
+		int use_bufpoi = (chip->options & NAND_USE_BOUNCE_BUFFER ?
+				  !virt_addr_valid(buf) : 0);
+		int part_pagewr = unlikely(column ||
+					   writelen < (mtd->writesize - 1));
+
+		/* Partial page write?, or need to use bounce buffer */
+		if (part_pagewr || use_bufpoi) {
+			pr_debug("%s: using write bounce buffer for buf@%p\n",
+					 __func__, buf);
 			cached = 0;
-			bytes = min_t(int, bytes - column, (int) writelen);
+			if (part_pagewr)
+				bytes = min_t(int,
+					      bytes - column, (int) writelen);
 			chip->pagebuf = -1;
 			memset(chip->buffers->databuf, 0xff, mtd->writesize);
 			memcpy(&chip->buffers->databuf[column], buf, bytes);
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 450d61e..bb3e064 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -176,6 +176,11 @@ typedef enum {
 /* Chip may not exist, so silence any errors in scan */
 #define NAND_SCAN_SILENT_NODEV	0x00040000
 /*
+ * This option is defined to protect against kmapped buffers
+ * being passed from highmem when using DMA
+ */
+#define NAND_USE_BOUNCE_BUFFER	0x00080000
+/*
  * Autodetect nand buswidth with readid/onfi.
  * This suppose the driver will configure the hardware in 8 bits mode
  * when calling nand_scan_ident, and update its configuration
-- 
1.9.2