[LEDE-DEV] [PATCH] ramips: Add patch to reset SPI flash to 3-byte addressing

[Daniel Golle]

Hi Alexandru,

On Mon, Jan 30, 2017 at 02:53:43PM -0800, Alexandru Gagniuc wrote:
> This patch is designed to workaround an issue where an mt7620 will
> hang after a reboot. This happens because the bootrom gets confused
> when the SPI flash is left in 4-byte addressing mode. This change
> makes sure that we can reboot the system under normal circumstances,
> but does not protect against system crashes.

NACK. This should not be needed and also doesn't provide a reliable
method to avoid the problem you describe, please rather try
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=3274ba26f27becfc4193ec6e229288140651f240

In case you are aware of boards which neither implement a proper
reset of the flash chip nor use a flash chip which supports dedicated
4-byte opcodes, please let us know, in that case the fix might still
be needed and at least provide a best-effort solution (which may still
result in stuck under certain circumstances such as CPU resets
triggered by watchdogs or in any way out of the kernel's control)

Cheers


Daniel

> 
> Signed-off-by: Alexandru Gagniuc <alex.g at adaptrum.com>
> ---
>  ...Reset-chip-to-3-byte-addressing-on-system.patch | 65 ++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>  create mode 100644 target/linux/ramips/patches-4.4/0800-mtd-m25p80-Reset-chip-to-3-byte-addressing-on-system.patch
> 
> diff --git a/target/linux/ramips/patches-4.4/0800-mtd-m25p80-Reset-chip-to-3-byte-addressing-on-system.patch b/target/linux/ramips/patches-4.4/0800-mtd-m25p80-Reset-chip-to-3-byte-addressing-on-system.patch
> new file mode 100644
> index 0000000..de4ee2c
> --- /dev/null
> +++ b/target/linux/ramips/patches-4.4/0800-mtd-m25p80-Reset-chip-to-3-byte-addressing-on-system.patch
> @@ -0,0 +1,65 @@
> +From 0f7fcc3dfc27a91e7672e9e589f3f558e8c41737 Mon Sep 17 00:00:00 2001
> +From: Alexandru Gagniuc <alex.g at adaptrum.com>
> +Date: Mon, 30 Jan 2017 13:30:33 -0800
> +Subject: [PATCH] mtd: m25p80: Reset chip to 3-byte addressing on system reboot
> +
> +Some SOCs can not handle 4-byte addressing in their mask ROM. On such
> +devices if we leave the SPI flash in 4-byte mode, then reboot the
> +system, the device will not boot.
> +
> +Some SoCs have a special output to reset all the on-board peripherals.
> +This pin should be connected to the !RESET pin of the flash as well.
> +Unfortunately, not all boards implement this. As a workaround for such
> +hardware, reset the SPI flash to 3-byte addressing mode. This does not
> +protect against system crashes, but it does allow the system to reboot
> +in the case of a normal reboot.
> +
> +Cc: Paul Fertser <fercerpav at gmail.com>
> +Signed-off-by: Alexandru Gagniuc <alex.g at adaptrum.com>
> +---
> + drivers/mtd/devices/m25p80.c | 15 +++++++++++++++
> + 1 file changed, 15 insertions(+)
> +
> +diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> +index fe9ceb7..2151975 100644
> +--- a/drivers/mtd/devices/m25p80.c
> ++++ b/drivers/mtd/devices/m25p80.c
> +@@ -27,6 +27,9 @@
> + #include <linux/spi/flash.h>
> + #include <linux/mtd/spi-nor.h>
> + 
> ++#define OPCODE_RESET_ENABLE	0x66
> ++#define OPCODE_RESET		0x99
> ++
> + #define	MAX_CMD_SIZE		6
> + struct m25p {
> + 	struct spi_device	*spi;
> +@@ -168,6 +171,17 @@ static int m25p80_erase(struct spi_nor *nor, loff_t offset)
> + 	return 0;
> + }
> + 
> ++void m25p80_reboot(struct mtd_info *mtd)
> ++{
> ++	struct spi_nor *nor = container_of(mtd, struct spi_nor, mtd);
> ++	struct m25p *flash = nor->priv;
> ++
> ++	flash->command[0] = OPCODE_RESET_ENABLE;
> ++	spi_write(flash->spi, flash->command, 1);
> ++	flash->command[0] = OPCODE_RESET;
> ++	spi_write(flash->spi, flash->command, 1);
> ++}
> ++
> + /*
> +  * board specific setup should have ensured the SPI clock used here
> +  * matches what the READ command supports, at least until this driver
> +@@ -197,6 +211,7 @@ static int m25p_probe(struct spi_device *spi)
> + 	nor->erase = m25p80_erase;
> + 	nor->write_reg = m25p80_write_reg;
> + 	nor->read_reg = m25p80_read_reg;
> ++	nor->mtd._reboot = m25p80_reboot;
> + 
> + 	nor->dev = &spi->dev;
> + 	nor->flash_node = spi->dev.of_node;
> +-- 
> +2.9.3
> +
> -- 
> 2.9.3
> 
> 
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