Patchwork mtd: spi-nor: add Kconfig option to disable 4K sectors

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Submitter Rafał Miłecki
Date Aug. 16, 2014, 8:17 p.m.
Message ID <1408220271-21455-1-git-send-email-zajec5@gmail.com>
Download mbox | patch
Permalink /patch/380505/
State Superseded
Commit d0eb06c9ea48979c33880d37d3c67e8c1b8ed105
Headers show

Comments

Rafał Miłecki - Aug. 16, 2014, 8:17 p.m.
Current situation with 4K sectors is quite messy. First of all, some
MTD "users" don't work with such small size. An example may be UBIFS
which requires 15 KiB erase blocks as a minimum. In theory spi-nor
should provide multiple erase regions and MTD "users" should use the
one they need. Unforunately that is not implemented.

In the result our flashes database in spi-nor is hackish. For some
flashes we pretend they don't support 4K sectors just because some
distribution users UBIFS on it. This ofc leads to conflicts, like
Samsung using w25q128 with 4K sectors vs. OpenWrt requiring it to
pretend it's 64 KiB blocks only.

My idea (plan?) for fixing this situation:
1) Use real hw info (this requires a way for disabling 4K for now)
2) Provide detailed info about erase regions
3) Make UBIFS work with devices that support 4K sectors

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
---
 drivers/mtd/spi-nor/Kconfig   | 11 +++++++++++
 drivers/mtd/spi-nor/spi-nor.c |  5 ++++-
 2 files changed, 15 insertions(+), 1 deletion(-)
Kevin Cernekee - Aug. 16, 2014, 9:06 p.m.
On Sat, Aug 16, 2014 at 1:17 PM, Rafał Miłecki <zajec5@gmail.com> wrote:
> +config MTD_SPI_NOR_USE_4K_SECTORS
> +       bool "Use small 4096 B erase sectors"
> +       default y
> +       help
> +         Many flash memories support erasing small (4096 B) sectors. Depending
> +         on the usage this feature may provide performance gain in comparison
> +         to erasing whole blocks (32/64 KiB).

I would also note that on some SPI-NOR devices, erasing 16x 4K sectors
is significantly slower than erasing 1x 64K block.  There is also the
question of balancing filesystem overhead versus internal
fragmentation.

It probably does make sense to let the user weigh the tradeoffs and
make the right decision for his application instead of hardcoding the
policy into the driver.

Patch

diff --git a/drivers/mtd/spi-nor/Kconfig b/drivers/mtd/spi-nor/Kconfig
index f8acfa4..601879e 100644
--- a/drivers/mtd/spi-nor/Kconfig
+++ b/drivers/mtd/spi-nor/Kconfig
@@ -7,6 +7,17 @@  menuconfig MTD_SPI_NOR
 
 if MTD_SPI_NOR
 
+config MTD_SPI_NOR_USE_4K_SECTORS
+	bool "Use small 4096 B erase sectors"
+	default y
+	help
+	  Many flash memories support erasing small (4096 B) sectors. Depending
+	  on the usage this feature may provide performance gain in comparison
+	  to erasing whole blocks (32/64 KiB).
+
+	  Please note that some tools/drivers/filesystems may not work with
+	  4096 B erase size (e.g. UBIFS requires 15 KiB as a minimum).
+
 config SPI_FSL_QUADSPI
 	tristate "Freescale Quad SPI controller"
 	depends on ARCH_MXC
diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index ba3f61e..ae16aa2 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -987,6 +987,7 @@  int spi_nor_scan(struct spi_nor *nor, const struct spi_device_id *id,
 	    nor->wait_till_ready == spi_nor_wait_till_ready)
 		nor->wait_till_ready = spi_nor_wait_till_fsr_ready;
 
+#ifdef CONFIG_MTD_SPI_NOR_USE_4K_SECTORS
 	/* prefer "small sector" erase if possible */
 	if (info->flags & SECT_4K) {
 		nor->erase_opcode = SPINOR_OP_BE_4K;
@@ -994,7 +995,9 @@  int spi_nor_scan(struct spi_nor *nor, const struct spi_device_id *id,
 	} else if (info->flags & SECT_4K_PMC) {
 		nor->erase_opcode = SPINOR_OP_BE_4K_PMC;
 		mtd->erasesize = 4096;
-	} else {
+	} else
+#endif
+	{
 		nor->erase_opcode = SPINOR_OP_SE;
 		mtd->erasesize = info->sector_size;
 	}