Subject: [PATCH] mtd: spi-nor: support limiting 4K sectors support based on flash size
From: Felix Fietkau <[email-masked]>
Date: Sat, 4 Nov 2017 07:40:23 +0100

Some devices need 4K sectors to be able to deal with small flash chips.
For instance, w25x05 is 64 KiB in size, and without 4K sectors, the
entire chip is just one erase block.
On bigger flash chip sizes, using 4K sectors can significantly slow down
many operations, including using a writable filesystem. There are several
platforms where it makes sense to use a single kernel on both kinds of
devices.

To support this properly, allow configuring an upper flash chip size
limit for 4K sectors support.

Signed-off-by: Felix Fietkau <[email-masked]>
---

--- a/drivers/mtd/spi-nor/Kconfig
+++ b/drivers/mtd/spi-nor/Kconfig
@@ -34,6 +34,17 @@ config SPI_ASPEED_SMC
 	  and support for the SPI flash memory controller (SPI) for
 	  the host firmware. The implementation only supports SPI NOR.
 
+config MTD_SPI_NOR_USE_4K_SECTORS_LIMIT
+	int "Maximum flash chip size to use 4K sectors on (in KiB)"
+	depends on MTD_SPI_NOR_USE_4K_SECTORS
+	default "4096"
+	help
+	  There are many flash chips that support 4K sectors, but are so large
+	  that using them significantly slows down writing large amounts of
+	  data or using a writable filesystem.
+	  Any flash chip larger than the size specified in this option will
+	  not use 4K sectors.
+
 config SPI_CADENCE_QUADSPI
 	tristate "Cadence Quad SPI controller"
 	depends on OF && (ARM || ARM64 || COMPILE_TEST)
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -4464,6 +4464,7 @@ static void spi_nor_info_init_params(str
 	struct spi_nor_erase_map *map = &params->erase_map;
 	const struct flash_info *info = nor->info;
 	struct device_node *np = spi_nor_get_flash_node(nor);
+	struct mtd_info *mtd = &nor->mtd;
 	u8 i, erase_mask;
 
 	/* Initialize legacy flash parameters and settings. */
@@ -4527,6 +4528,21 @@ static void spi_nor_info_init_params(str
 	 */
 	erase_mask = 0;
 	i = 0;
+#ifdef CONFIG_MTD_SPI_NOR_USE_4K_SECTORS
+	if ((info->flags & SECT_4K_PMC) && (mtd->size <=
+		   CONFIG_MTD_SPI_NOR_USE_4K_SECTORS_LIMIT * 1024)) {
+		erase_mask |= BIT(i);
+		spi_nor_set_erase_type(&map->erase_type[i], 4096u,
+				       SPINOR_OP_BE_4K_PMC);
+		i++;
+	} else if ((info->flags & SECT_4K) && (mtd->size <=
+	    CONFIG_MTD_SPI_NOR_USE_4K_SECTORS_LIMIT * 1024)) {
+		erase_mask |= BIT(i);
+		spi_nor_set_erase_type(&map->erase_type[i], 4096u,
+				       SPINOR_OP_BE_4K);
+		i++;
+	}
+#else
 	if (info->flags & SECT_4K_PMC) {
 		erase_mask |= BIT(i);
 		spi_nor_set_erase_type(&map->erase_type[i], 4096u,
@@ -4538,6 +4554,7 @@ static void spi_nor_info_init_params(str
 				       SPINOR_OP_BE_4K);
 		i++;
 	}
+#endif
 	erase_mask |= BIT(i);
 	spi_nor_set_erase_type(&map->erase_type[i], info->sector_size,
 			       SPINOR_OP_SE);