mtd: spinand: add support of continuous reading mode

The code was ported from linux-6.12. The original continuous reading
support was implemented by Miquel Raynal <[email protected]>
in linux commit 631cfdd0520d (mtd: spi-nand: Add continuous read support).

Here is an original patch description:
--------------------------------------
A regular page read consist in:
- Asking one page of content from the NAND array to be loaded in the
  chip's SRAM,
- Waiting for the operation to be done,
- Retrieving the data (I/O phase) from the chip's SRAM.

When reading several sequential pages, the above operation is repeated
over and over. There is however a way to optimize these accesses, by
enabling continuous reads. The feature requires the NAND chip to have a
second internal SRAM area plus a bit of additional internal logic to
trigger another internal transfer between the NAND array and the second
SRAM area while the I/O phase is ongoing. Once the first I/O phase is
done, the host can continue reading more data, continuously, as the chip
will automatically switch to the second SRAM content (which has already
been loaded) and in turns trigger the next load into the first SRAM area
again.

From an instruction perspective, the command op-codes are different, but
the same cycles are required. The only difference is that after a
continuous read (which is stopped by a CS deassert), the host must
observe a delay of tRST. However, because there is no guarantee in Linux
regarding the actual state of the CS pin after a transfer (in order to
speed-up the next transfer if targeting the same device), it was
necessary to manually end the continuous read with a configuration
register write operation.

Continuous reads have two main drawbacks:
* They only work on full pages (column address ignored)
* Only the main data area is pulled, out-of-band bytes are not
  accessible. Said otherwise, the feature can only be useful with on-die
  ECC engines.

Performance wise, measures have been performed on a Zynq platform using
Macronix SPI-NAND controller with a Macronix chip (based on the
flash_speed tool modified for testing sequential reads):
- 1-1-1 mode: performances improved from +3% (2-pages) up to +10% after
              a dozen pages.
- 1-1-4 mode: performances improved from +15% (2-pages) up to +40% after
              a dozen pages.

This series is based on a previous work from Macronix engineer Jaime
Liao.
--------------------------------------

Signed-off-by: Mikhail Kshevetskiy <[email protected]>
Reviewed-by: Frieder Schrempf <[email protected]>
Signed-off-by: Michael Trimarchi <[email protected]>

2 files changed, 100 insertions, 9 deletions

diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 910ef56ed0c..9285edd5c4b 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -101,6 +101,8 @@ enum nand_page_io_req_type {
  * @ooblen: the number of OOB bytes to read from/write to this page
  * @oobbuf: buffer to store OOB data in or get OOB data from
  * @mode: one of the %MTD_OPS_XXX mode
+ * @continuous: no need to start over the operation at the end of each page, the
+ * NAND device will automatically prepare the next one
  *
  * This object is used to pass per-page I/O requests to NAND sub-layers. This
  * way all useful information are already formatted in a useful way and
@@ -123,6 +125,7 @@ struct nand_page_io_req {
 		void *in;
 	} oobbuf;
 	int mode;
+	bool continuous;
 };
 
 /**
@@ -638,19 +641,19 @@ static inline void nanddev_pos_next_page(struct nand_device *nand,
 }
 
 /**
- * nand_io_iter_init - Initialize a NAND I/O iterator
+ * nand_io_page_iter_init - Initialize a NAND I/O iterator
  * @nand: NAND device
  * @offs: absolute offset
  * @req: MTD request
  * @iter: NAND I/O iterator
  *
  * Initializes a NAND iterator based on the information passed by the MTD
- * layer.
+ * layer for page jumps.
  */
-static inline void nanddev_io_iter_init(struct nand_device *nand,
-					enum nand_page_io_req_type reqtype,
-					loff_t offs, struct mtd_oob_ops *req,
-					struct nand_io_iter *iter)
+static inline void nanddev_io_page_iter_init(struct nand_device *nand,
+					     enum nand_page_io_req_type reqtype,
+					     loff_t offs, struct mtd_oob_ops *req,
+					     struct nand_io_iter *iter)
 {
 	struct mtd_info *mtd = nanddev_to_mtd(nand);
 
@@ -669,6 +672,43 @@ static inline void nanddev_io_iter_init(struct nand_device *nand,
 	iter->req.ooblen = min_t(unsigned int,
 				 iter->oobbytes_per_page - iter->req.ooboffs,
 				 iter->oobleft);
+	iter->req.continuous = false;
+}
+
+/**
+ * nand_io_block_iter_init - Initialize a NAND I/O iterator
+ * @nand: NAND device
+ * @offs: absolute offset
+ * @req: MTD request
+ * @iter: NAND I/O iterator
+ *
+ * Initializes a NAND iterator based on the information passed by the MTD
+ * layer for block jumps (no OOB)
+ *
+ * In practice only reads may leverage this iterator.
+ */
+static inline void nanddev_io_block_iter_init(struct nand_device *nand,
+					      enum nand_page_io_req_type reqtype,
+					      loff_t offs, struct mtd_oob_ops *req,
+					      struct nand_io_iter *iter)
+{
+	unsigned int offs_in_eb;
+
+	iter->req.type = reqtype;
+	iter->req.mode = req->mode;
+	iter->req.dataoffs = nanddev_offs_to_pos(nand, offs, &iter->req.pos);
+	iter->req.ooboffs = 0;
+	iter->oobbytes_per_page = 0;
+	iter->dataleft = req->len;
+	iter->oobleft = 0;
+	iter->req.databuf.in = req->datbuf;
+	offs_in_eb = (nand->memorg.pagesize * iter->req.pos.page) + iter->req.dataoffs;
+	iter->req.datalen = min_t(unsigned int,
+				  nanddev_eraseblock_size(nand) - offs_in_eb,
+				  iter->dataleft);
+	iter->req.oobbuf.in = NULL;
+	iter->req.ooblen = 0;
+	iter->req.continuous = true;
 }
 
 /**
@@ -695,6 +735,25 @@ static inline void nanddev_io_iter_next_page(struct nand_device *nand,
 }
 
 /**
+ * nand_io_iter_next_block - Move to the next block
+ * @nand: NAND device
+ * @iter: NAND I/O iterator
+ *
+ * Updates the @iter to point to the next block.
+ * No OOB handling available.
+ */
+static inline void nanddev_io_iter_next_block(struct nand_device *nand,
+					      struct nand_io_iter *iter)
+{
+	nanddev_pos_next_eraseblock(nand, &iter->req.pos);
+	iter->dataleft -= iter->req.datalen;
+	iter->req.databuf.in += iter->req.datalen;
+	iter->req.dataoffs = 0;
+	iter->req.datalen = min_t(unsigned int, nanddev_eraseblock_size(nand),
+				  iter->dataleft);
+}
+
+/**
  * nand_io_iter_end - Should end iteration or not
  * @nand: NAND device
  * @iter: NAND I/O iterator
@@ -722,13 +781,28 @@ static inline bool nanddev_io_iter_end(struct nand_device *nand,
  * @req: MTD I/O request
  * @iter: NAND I/O iterator
  *
- * Should be used for iterate over pages that are contained in an MTD request.
+ * Should be used for iterating over pages that are contained in an MTD request.
  */
 #define nanddev_io_for_each_page(nand, type, start, req, iter)		\
-	for (nanddev_io_iter_init(nand, type, start, req, iter);	\
+	for (nanddev_io_page_iter_init(nand, type, start, req, iter);	\
 	     !nanddev_io_iter_end(nand, iter);				\
 	     nanddev_io_iter_next_page(nand, iter))
 
+/**
+ * nand_io_for_each_block - Iterate over all NAND pages contained in an MTD I/O
+ *			    request, one block at a time
+ * @nand: NAND device
+ * @start: start address to read/write from
+ * @req: MTD I/O request
+ * @iter: NAND I/O iterator
+ *
+ * Should be used for iterating over blocks that are contained in an MTD request.
+ */
+#define nanddev_io_for_each_block(nand, type, start, req, iter)		\
+	for (nanddev_io_block_iter_init(nand, type, start, req, iter);	\
+	     !nanddev_io_iter_end(nand, iter);				\
+	     nanddev_io_iter_next_block(nand, iter))
+
 bool nanddev_isbad(struct nand_device *nand, const struct nand_pos *pos);
 bool nanddev_isreserved(struct nand_device *nand, const struct nand_pos *pos);
 int nanddev_markbad(struct nand_device *nand, const struct nand_pos *pos);
diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
index 63626c9c27c..2f8212e4037 100644
--- a/include/linux/mtd/spinand.h
+++ b/include/linux/mtd/spinand.h
@@ -175,7 +175,7 @@
 struct spinand_op;
 struct spinand_device;
 
-#define SPINAND_MAX_ID_LEN	4
+#define SPINAND_MAX_ID_LEN	5
 /*
  * For erase, write and read operation, we got the following timings :
  * tBERS (erase) 1ms to 4ms
@@ -336,6 +336,7 @@ struct spinand_ecc_info {
  * @op_variants.update_cache: variants of the update-cache operation
  * @select_target: function used to select a target/die. Required only for
  *		   multi-die chips
+ * @set_cont_read: enable/disable continuous cached reads
  *
  * Each SPI NAND manufacturer driver should have a spinand_info table
  * describing all the chips supported by the driver.
@@ -354,6 +355,8 @@ struct spinand_info {
 	} op_variants;
 	int (*select_target)(struct spinand_device *spinand,
 			     unsigned int target);
+	int (*set_cont_read)(struct spinand_device *spinand,
+			     bool enable);
 };
 
 #define SPINAND_ID(__method, ...)					\
@@ -379,6 +382,9 @@ struct spinand_info {
 #define SPINAND_SELECT_TARGET(__func)					\
 	.select_target = __func,
 
+#define SPINAND_CONT_READ(__set_cont_read)				\
+	.set_cont_read = __set_cont_read,
+
 #define SPINAND_INFO(__model, __id, __memorg, __eccreq, __op_variants,	\
 		     __flags, ...)					\
 	{								\
@@ -422,6 +428,12 @@ struct spinand_dirmap {
  *		passed in spi_mem_op be DMA-able, so we can't based the bufs on
  *		the stack
  * @manufacturer: SPI NAND manufacturer information
+ * @cont_read_possible: Field filled by the core once the whole system
+ *		configuration is known to tell whether continuous reads are
+ *		suitable to use or not in general with this chip/configuration.
+ *		A per-transfer check must of course be done to ensure it is
+ *		actually relevant to enable this feature.
+ * @set_cont_read: Enable/disable the continuous read feature
  * @priv: manufacturer private data
  * @last_wait_status: status of the last wait operation that will be used in case
  *		      ->get_status() is not populated by the spinand device.
@@ -457,7 +469,12 @@ struct spinand_device {
 	u8 *scratchbuf;
 	const struct spinand_manufacturer *manufacturer;
 	void *priv;
+
 	u8 last_wait_status;
+
+	bool cont_read_possible;
+	int (*set_cont_read)(struct spinand_device *spinand,
+			     bool enable);
 };
 
 /**