[PATCH v2 05/30] mtd: spi-nor: Add support for cross die read in dual flash configuration

[Tejas Bhumkar]

From: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>

In a dual parallel configuration, halve the read offset.
Determine whether the read offset points to the lower or
upper flash in a dual stacked configuration and set the
corresponding flags accordingly.

Include support for cases where the read involves an odd
number of bytes.

Extend support for cross-die reads in flash memory devices
that contain multiple dies within them.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>
Signed-off-by: Michal Simek <michal.simek at xilinx.com>
Signed-off-by: Tejas Bhumkar <tejas.arvind.bhumkar at amd.com>
---
 drivers/mtd/spi/spi-nor-core.c | 61 ++++++++++++++++++++++++++++++----
 include/spi.h                  |  3 +-
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index e505648e5d..f6e7592458 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -1503,11 +1503,8 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
 	struct spi_nor *nor = mtd_to_spi_nor(mtd);
 	int ret;
 	u32 offset = from;
-	u32 stack_shift = 0;
-	u32 read_len = 0;
-	u32 rem_bank_len = 0;
-	u8 bank;
-	u8 is_ofst_odd = 0;
+	u32 bank_size, stack_shift = 0, read_len = 0, rem_bank_len = 0;
+	u8 bank, cur_bank, nxt_bank, is_ofst_odd = 0;
 
 	dev_dbg(nor->dev, "from 0x%08x, len %zd\n", (u32)from, len);
 
@@ -1541,6 +1538,40 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
 			}
 		}
 
+		if (nor->addr_width == 4) {
+			/*
+			 * Some flash devices like N25Q512 have multiple dies
+			 * in it. Read operation in these devices is bounded
+			 * by its die segment. In a continuous read, across
+			 * multiple dies, when the last byte of the selected
+			 * die segment is read, the next byte read is the
+			 * first byte of the same die segment. This is Die
+			 * cross over issue. So to handle this issue, split
+			 * a read transaction, that spans across multiple
+			 * banks, into one read per bank. Bank size is 16MB
+			 * for single and dual stacked mode and 32MB for dual
+			 * parallel mode.
+			 */
+			if (nor->spi && nor->spi->multi_die) {
+				bank_size = SZ_16M;
+				if (nor->flags & SNOR_F_HAS_PARALLEL)
+					bank_size <<= 1;
+				cur_bank = offset / bank_size;
+				nxt_bank = (offset + len) / bank_size;
+				if (cur_bank != nxt_bank)
+					rem_bank_len = (bank_size *
+							(cur_bank + 1)) -
+							offset;
+				else
+					rem_bank_len = (mtd->size >>
+							stack_shift) -
+							offset;
+			} else {
+				rem_bank_len = (mtd->size >> stack_shift) -
+						offset;
+			}
+		}
+
 		if (nor->flags & SNOR_F_HAS_PARALLEL)
 			offset /= 2;
 
@@ -1552,6 +1583,15 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
 #endif
 		}
 
+		if (len < rem_bank_len)
+			read_len = len;
+		else
+			read_len = rem_bank_len;
+
+		ret = spi_nor_wait_till_ready(nor);
+		if (ret)
+			goto read_err;
+
 		ret = nor->read(nor, offset, read_len, buf);
 		if (ret == 0) {
 			/* We shouldn't see 0-length reads */
@@ -1561,8 +1601,15 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
 		if (ret < 0)
 			goto read_err;
 
-		*retlen += ret;
-		buf += ret;
+		if (is_ofst_odd == 1) {
+			memcpy(buf, (buf + 1), (len - 1));
+			*retlen += (ret - 1);
+			buf += ret - 1;
+			is_ofst_odd = 0;
+		} else {
+			*retlen += ret;
+			buf += ret;
+		}
 		from += ret;
 		len -= ret;
 	}
diff --git a/include/spi.h b/include/spi.h
index eb015ecbf5..9014066ee3 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -165,7 +165,7 @@ struct spi_slave {
 	unsigned int max_write_size;
 	void *memory_map;
 
-	u8 flags;
+	u32 flags;
 #define SPI_XFER_BEGIN		BIT(0)	/* Assert CS before transfer */
 #define SPI_XFER_END		BIT(1)	/* Deassert CS after transfer */
 #define SPI_XFER_ONCE		(SPI_XFER_BEGIN | SPI_XFER_END)
@@ -179,6 +179,7 @@ struct spi_slave {
 	 */
 	bool multi_cs_cap;
 	u32 bytemode;
+	bool multi_die;			/* flash with multiple dies */
 };
 
 /**
-- 
2.27.0