linux-kernel - [PATCH 3/3] mtd: spi-nor: core: Introduce SPI_NOR_NO_MULTI_PASS

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Date:   Mon, 12 Oct 2020 23:34:04 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
CC:     Pratyush Yadav <p.yadav@...com>
Subject: [PATCH 3/3] mtd: spi-nor: core: Introduce SPI_NOR_NO_MULTI_PASS_PP

The Cypress Semper S28 flash family uses 2-bit ECC by default. Under
this ECC scheme, multi-pass page programs result in a program error.
This means that unlike many other SPI NOR flashes, bit-walking cannot be
done. In other words, once a page is programmed, its bits cannot then be
flipped to 0 without an erase in between.

This causes problems with UBIFS because it uses bit-walking to clear EC
and VID magic numbers from a PEB before issuing an erase to preserve the
file system correctness in case of power cuts.

Use SPI_NOR_NO_MULTI_PASS_PP to set MTD_NO_MULTI_PASS_WRITE, telling
upper layers to avoid multi-pass page programming. In addition, update
mtd->writesize to match the page size to make sure upper layers make the
changes they need in one single go.

Signed-off-by: Pratyush Yadav <p.yadav@...com>
---
 drivers/mtd/spi-nor/core.c     | 5 +++++
 drivers/mtd/spi-nor/core.h     | 6 ++++++
 drivers/mtd/spi-nor/spansion.c | 2 +-
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ff592468cc15..16d4bcfe7b10 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3469,6 +3469,11 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	nor->page_size = nor->params->page_size;
 	mtd->writebufsize = nor->page_size;
 
+	if (info->flags & SPI_NOR_NO_MULTI_PASS_PP) {
+		mtd->flags |= MTD_NO_MULTI_PASS_WRITE;
+		mtd->writesize = nor->page_size;
+	}
+
 	if (of_property_read_bool(np, "broken-flash-reset"))
 		nor->flags |= SNOR_F_BROKEN_RESET;
 
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index 0a775a7b5606..3394b7474c08 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -329,6 +329,12 @@ struct flash_info {
 						 * available I/O mode via a
 						 * volatile bit.
 						 */
+#define SPI_NOR_NO_MULTI_PASS_PP	BIT(22) /*
+						 * Once a page is programmed it
+						 * cannot be programmed again
+						 * without an erase operation in
+						 * between.
+						 */
 
 	/* Part specific fixup hooks. */
 	const struct spi_nor_fixups *fixups;
diff --git a/drivers/mtd/spi-nor/spansion.c b/drivers/mtd/spi-nor/spansion.c
index 2c5c0f69dc5c..72430cd4e6af 100644
--- a/drivers/mtd/spi-nor/spansion.c
+++ b/drivers/mtd/spi-nor/spansion.c
@@ -275,7 +275,7 @@ static const struct flash_info spansion_parts[] = {
 			      SPI_NOR_NO_ERASE) },
 	{ "s28hs512t",   INFO(0x345b1a,      0, 256 * 1024, 256,
 			     SECT_4K | SPI_NOR_OCTAL_DTR_READ |
-			      SPI_NOR_OCTAL_DTR_PP)
+			      SPI_NOR_OCTAL_DTR_PP | SPI_NOR_NO_MULTI_PASS_PP)
 	  .fixups = &s28hs512t_fixups,
 	},
 };
-- 
2.28.0