mtd: spi-nor: spansion: Enable JFFS2 write buffer for Infineon s28hx SEMPER flash

Infineon(Cypress) SEMPER NOR flash family has on-die ECC and its program
granularity is 16-byte ECC data unit size. JFFS2 supports write buffer
mode for ECC'd NOR flash. Provide a way to clear the MTD_BIT_WRITEABLE
flag in order to enable JFFS2 write buffer mode support.

A new SNOR_F_ECC flag is introduced to determine if the part has on-die
ECC and if it has, MTD_BIT_WRITEABLE is unset.

In vendor specific driver, a common cypress_nor_ecc_init() helper is
added. This helper takes care for ECC related initialization for SEMPER
flash family by setting up params->writesize and SNOR_F_ECC.

Fixes: c3266af ("mtd: spi-nor: spansion: add support for Cypress Semper flash")
Suggested-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/d586723f6f12aaff44fbcd7b51e674b47ed554ed.1680760742.git.Takahiro.Kuwano@infineon.com
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>

Author: Kuwano-san

drivers/mtd/spi-nor/core.c

@@ -3407,6 +3407,9 @@ static void spi_nor_set_mtd_info(struct spi_nor *nor)
 		mtd->name = dev_name(dev);
 	mtd->type = MTD_NORFLASH;
 	mtd->flags = MTD_CAP_NORFLASH;
+	/* Unset BIT_WRITEABLE to enable JFFS2 write buffer for ECC'd NOR */
+	if (nor->flags & SNOR_F_ECC)
+		mtd->flags &= ~MTD_BIT_WRITEABLE;
 	if (nor->info->flags & SPI_NOR_NO_ERASE)
 		mtd->flags |= MTD_NO_ERASE;
 	else

drivers/mtd/spi-nor/core.h

@@ -131,6 +131,7 @@ enum spi_nor_option_flags {
 	SNOR_F_SOFT_RESET	= BIT(12),
 	SNOR_F_SWP_IS_VOLATILE	= BIT(13),
 	SNOR_F_RWW		= BIT(14),
+	SNOR_F_ECC		= BIT(15),
 };
 
 struct spi_nor_read_command {

drivers/mtd/spi-nor/debugfs.c

@@ -26,6 +26,7 @@ static const char *const snor_f_names[] = {
 	SNOR_F_NAME(SOFT_RESET),
 	SNOR_F_NAME(SWP_IS_VOLATILE),
 	SNOR_F_NAME(RWW),
+	SNOR_F_NAME(ECC),
 };
 #undef SNOR_F_NAME
 

drivers/mtd/spi-nor/spansion.c

@@ -332,6 +332,17 @@ static int cypress_nor_set_page_size(struct spi_nor *nor)
 	return 0;
 }
 
+static void cypress_nor_ecc_init(struct spi_nor *nor)
+{
+	/*
+	 * Programming is supported only in 16-byte ECC data unit granularity.
+	 * Byte-programming, bit-walking, or multiple program operations to the
+	 * same ECC data unit without an erase are not allowed.
+	 */
+	nor->params->writesize = 16;
+	nor->flags |= SNOR_F_ECC;
+}
+
 static int
 s25fs256t_post_bfpt_fixup(struct spi_nor *nor,
 			  const struct sfdp_parameter_header *bfpt_header,
@@ -506,7 +517,7 @@ static int s28hx_t_post_bfpt_fixup(struct spi_nor *nor,
 static void s28hx_t_late_init(struct spi_nor *nor)
 {
 	nor->params->octal_dtr_enable = cypress_nor_octal_dtr_enable;
-	nor->params->writesize = 16;
+	cypress_nor_ecc_init(nor);
 }
 
 static const struct spi_nor_fixups s28hx_t_fixups = {