[PATCH v2] spi: spi-qpic-snand: fix calculating of ECC OOB regions' properties

[Gabor Juhos <j4g8y7@gmail.com>]

The OOB layout used by the driver has two distinct regions which contains
hardware specific ECC data, yet the qcom_spi_ooblayout_ecc() function sets
the same offset and length values for both regions which is clearly wrong.

Change the code to calculate the correct values for both regions.

For reference, the following table shows the computed offset and length
values for various OOB size/ECC strength configurations:

                              +-----------------+-----------------+
                              |before the change| after the change|
  +-------+----------+--------+--------+--------+--------+--------+
  |  OOB  |   ECC    | region | region | region | region | region |
  |  size | strength | index  | offset | length | offset | length |
  +-------+----------+--------+--------+--------+--------+--------+
  |  128  |     8    |    0   |   113  |   15   |    0   |   49   |
  |       |          |    1   |   113  |   15   |   65   |   63   |
  +-------+----------+--------+--------+--------+--------+--------+
  |  128  |     4    |    0   |   117  |   11   |    0   |   37   |
  |       |          |    1   |   117  |   11   |   53   |   75   |
  +-------+----------+--------+--------+--------+--------+--------+
  |   64  |     4    |    0   |    53  |   11   |    0   |   37   |
  |       |          |    1   |    53  |   11   |   53   |   11   |
  +-------+----------+--------+--------+--------+--------+--------+

Fixes: 7304d1909080 ("spi: spi-qpic: add driver for QCOM SPI NAND flash Interface")
Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
---
Changes in v2:
  - use switch statement to handle section numbers
  - reject negative section numbers as out-of-range
  - Link to v1: https://lore.kernel.org/r/20250731-qpic-snand-oob-ecc-fix-v1-1-29ba1c6f94e5@gmail.com
---
 drivers/spi/spi-qpic-snand.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-qpic-snand.c b/drivers/spi/spi-qpic-snand.c
index 0cfa0d960fd3c245c2bbf4f5e02d0fc0b13e7696..53205d5037dc4fd58a69063532b20ab10c652694 100644
--- a/drivers/spi/spi-qpic-snand.c
+++ b/drivers/spi/spi-qpic-snand.c
@@ -210,13 +210,21 @@ static int qcom_spi_ooblayout_ecc(struct mtd_info *mtd, int section,
 	struct qcom_nand_controller *snandc = nand_to_qcom_snand(nand);
 	struct qpic_ecc *qecc = snandc->qspi->ecc;
 
-	if (section > 1)
-		return -ERANGE;
-
-	oobregion->length = qecc->ecc_bytes_hw + qecc->spare_bytes;
-	oobregion->offset = mtd->oobsize - oobregion->length;
+	switch (section) {
+	case 0:
+		oobregion->offset = 0;
+		oobregion->length = qecc->bytes * (qecc->steps - 1) +
+				    qecc->bbm_size;
+		return 0;
+	case 1:
+		oobregion->offset = qecc->bytes * (qecc->steps - 1) +
+				    qecc->bbm_size +
+				    qecc->steps * 4;
+		oobregion->length = mtd->oobsize - oobregion->offset;
+		return 0;
+	}
 
-	return 0;
+	return -ERANGE;
 }
 
 static int qcom_spi_ooblayout_free(struct mtd_info *mtd, int section,

---
base-commit: 926406a85ad895fbe6ee4577cdbc4f55245a0742
change-id: 20250731-qpic-snand-oob-ecc-fix-8d3d80cc8680

Best regards,
-- 
Gabor Juhos <j4g8y7@gmail.com>