[RESEND PATCH v2] mtd: rawnand: micron: Adapt the PAGE READ flow to constraint controllers

[Miquel Raynal <miquel.raynal@xxxxxxxxxxx>]

There are controllers not able to just read data cycles on the
bus. There are controllers not able to do a change column.

If we want to support both, we need to check which operation is
supported first. This is the exact same mechanism that is in use for
parameter page reads (ONFI/JEDEC) as the same problem occurs.

Speed testing does not show any throughput penalty so we do not
optimize more than that. However it is likely that, in the future, a
more robust and exhaustive test will run at boot time to avoid
re-checking what is supported and what is not at every call.

Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---

Resent:
* Actually integrate the comments...

Changes in v2:
* Added a comment before each check which is a condensate of the
  commit message.  

 drivers/mtd/nand/raw/nand_micron.c | 61 +++++++++++++++++++++++++-----
 1 file changed, 52 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
index b2b047b245f4..3589b4fce0d4 100644
--- a/drivers/mtd/nand/raw/nand_micron.c
+++ b/drivers/mtd/nand/raw/nand_micron.c
@@ -192,6 +192,7 @@ static int micron_nand_on_die_ecc_status_4(struct nand_chip *chip, u8 status,
 	struct micron_nand *micron = nand_get_manufacturer_data(chip);
 	struct mtd_info *mtd = nand_to_mtd(chip);
 	unsigned int step, max_bitflips = 0;
+	bool use_datain = false;
 	int ret;
 
 	if (!(status & NAND_ECC_STATUS_WRITE_RECOMMENDED)) {
@@ -211,8 +212,27 @@ static int micron_nand_on_die_ecc_status_4(struct nand_chip *chip, u8 status,
 	 * in non-raw mode, even if the user did not request those bytes.
 	 */
 	if (!oob_required) {
-		ret = nand_read_data_op(chip, chip->oob_poi, mtd->oobsize,
-					false, false);
+		/*
+		 * We first check which operation is supported by the controller
+		 * before running it. This trick makes it possible to support
+		 * all controllers, even the most constraints, without almost
+		 * any performance hit.
+		 *
+		 * TODO: could be enhanced to avoid repeating the same check
+		 * over and over in the fast path.
+		 */
+		if (!nand_has_exec_op(chip) ||
+		    !nand_read_data_op(chip, chip->oob_poi, mtd->oobsize, false,
+				       true))
+			use_datain = true;
+
+		if (use_datain)
+			ret = nand_read_data_op(chip, chip->oob_poi,
+						mtd->oobsize, false, false);
+		else
+			ret = nand_change_read_column_op(chip, mtd->writesize,
+							 chip->oob_poi,
+							 mtd->oobsize, false);
 		if (ret)
 			return ret;
 	}
@@ -285,6 +305,7 @@ micron_nand_read_page_on_die_ecc(struct nand_chip *chip, uint8_t *buf,
 				 int oob_required, int page)
 {
 	struct mtd_info *mtd = nand_to_mtd(chip);
+	bool use_datain = false;
 	u8 status;
 	int ret, max_bitflips = 0;
 
@@ -300,14 +321,36 @@ micron_nand_read_page_on_die_ecc(struct nand_chip *chip, uint8_t *buf,
 	if (ret)
 		goto out;
 
-	ret = nand_exit_status_op(chip);
-	if (ret)
-		goto out;
+	/*
+	 * We first check which operation is supported by the controller before
+	 * running it. This trick makes it possible to support all controllers,
+	 * even the most constraints, without almost any performance hit.
+	 *
+	 * TODO: could be enhanced to avoid repeating the same check over and
+	 * over in the fast path.
+	 */
+	if (!nand_has_exec_op(chip) ||
+	    !nand_read_data_op(chip, buf, mtd->writesize, false, true))
+		use_datain = true;
 
-	ret = nand_read_data_op(chip, buf, mtd->writesize, false, false);
-	if (!ret && oob_required)
-		ret = nand_read_data_op(chip, chip->oob_poi, mtd->oobsize,
-					false, false);
+	if (use_datain) {
+		ret = nand_exit_status_op(chip);
+		if (ret)
+			goto out;
+
+		ret = nand_read_data_op(chip, buf, mtd->writesize, false,
+					false);
+		if (!ret && oob_required)
+			ret = nand_read_data_op(chip, chip->oob_poi,
+						mtd->oobsize, false, false);
+	} else {
+		ret = nand_change_read_column_op(chip, 0, buf, mtd->writesize,
+						 false);
+		if (!ret && oob_required)
+			ret = nand_change_read_column_op(chip, mtd->writesize,
+							 chip->oob_poi,
+							 mtd->oobsize, false);
+	}
 
 	if (chip->ecc.strength == 4)
 		max_bitflips = micron_nand_on_die_ecc_status_4(chip, status,
-- 
2.20.1


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