[PATCH v3 14/17] mtd: spi-nor-core: Perform a Soft Reset on shutdown

[Jagan Teki <jagan@amarulasolutions.com>]

On Mon, Mar 30, 2020 at 9:16 PM Pratyush Yadav <p.yadav@ti.com> wrote:
>
> On probe, the SPI NOR core will put a flash in 8D-8D-8D mode if it
> supports it. But Linux as of now expects to get the flash in 1S-1S-1S
> mode. Handing the flash to Linux in Octal DTR mode means the kernel will
> fail to detect the flash.
>
> So, we need to reset to Power-on-Reset (POR) state before handing off
> the flash. A Software Reset command can be used to do this. Since the
> command is optional, flashes have to specify they support it by using
> the flag 'SPI_NOR_SOFT_RESET'.
>
> One limitation of the soft reset is that it will restore state from
> non-volatile registers in some flashes. This means that if the flash was
> set to 8D mode in a non-volatile configuration, a soft reset won't help.
> This commit assumes that we don't set any non-volatile bits anywhere,
> and the flash doesn't have any non-volatile Octal DTR mode
> configuration.

Is this common for all 8D supported flash devices?

>
> Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
> ---
>  drivers/mtd/spi/sf_internal.h  |  1 +
>  drivers/mtd/spi/sf_probe.c     |  9 +++++
>  drivers/mtd/spi/spi-nor-core.c | 66 ++++++++++++++++++++++++++++++++++
>  include/linux/mtd/spi-nor.h    | 11 ++++++
>  4 files changed, 87 insertions(+)
>
> diff --git a/drivers/mtd/spi/sf_internal.h b/drivers/mtd/spi/sf_internal.h
> index 5780c81287..37e6657490 100644
> --- a/drivers/mtd/spi/sf_internal.h
> +++ b/drivers/mtd/spi/sf_internal.h
> @@ -68,6 +68,7 @@ struct flash_info {
>  #define SPI_NOR_HAS_SST26LOCK  BIT(15) /* Flash supports lock/unlock via BPR */
>  #define SPI_NOR_OCTAL_READ      BIT(16) /* Flash supports Octal Read */
>  #define SPI_NOR_OCTAL_DTR_READ BIT(17) /* Flash supports Octal DTR Read */
> +#define SPI_NOR_SOFT_RESET     BIT(18) /* Flash supports soft reset command */
>
>         /* Part specific fixup hooks. */
>         const struct spi_nor_fixups *fixups;
> diff --git a/drivers/mtd/spi/sf_probe.c b/drivers/mtd/spi/sf_probe.c
> index 72b6ee702d..90bd3196c2 100644
> --- a/drivers/mtd/spi/sf_probe.c
> +++ b/drivers/mtd/spi/sf_probe.c
> @@ -152,6 +152,14 @@ int spi_flash_std_probe(struct udevice *dev)
>
>  static int spi_flash_std_remove(struct udevice *dev)
>  {
> +       struct spi_flash *flash;
> +       int ret;
> +
> +       flash = dev_get_uclass_priv(dev);
> +       ret = spi_nor_remove(flash);
> +       if (ret)
> +               return ret;
> +
>  #if CONFIG_IS_ENABLED(SPI_FLASH_MTD)
>         spi_flash_mtd_unregister();
>  #endif
> @@ -178,6 +186,7 @@ U_BOOT_DRIVER(spi_flash_std) = {
>         .remove         = spi_flash_std_remove,
>         .priv_auto_alloc_size = sizeof(struct spi_flash),
>         .ops            = &spi_flash_std_ops,
> +       .flags          = DM_FLAG_OS_PREPARE,
>  };
>
>  #endif /* CONFIG_DM_SPI_FLASH */
> diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
> index 5b995cda3f..52b3775035 100644
> --- a/drivers/mtd/spi/spi-nor-core.c
> +++ b/drivers/mtd/spi/spi-nor-core.c
> @@ -186,6 +186,8 @@ struct spi_nor_fixups {
>                           struct spi_nor_flash_parameter *params);
>  };
>
> +#define SPI_NOR_SRST_SLEEP_LEN                 200
> +
>  /**
>   * spi_nor_get_cmd_ext() - Get the command opcode extension based on the
>   *                        extension type.
> @@ -2835,6 +2837,67 @@ static int spi_nor_init(struct spi_nor *nor)
>         return 0;
>  }
>
> +/**
> + * spi_nor_soft_reset() - perform the JEDEC Software Reset sequence
> + * @nor:       the spi_nor structure
> + *
> + * This function can be used to switch from Octal DTR mode to legacy mode on a
> + * flash that supports it. The soft reset is executed in Octal DTR mode.
> + *
> + * Return: 0 for success, -errno for failure.
> + */
> +static int spi_nor_soft_reset(struct spi_nor *nor)
> +{
> +       struct spi_mem_op op;
> +       int ret;
> +       enum spi_nor_cmd_ext ext;
> +
> +       ext = nor->cmd_ext_type;
> +       nor->cmd_ext_type = SPI_NOR_EXT_REPEAT;
> +
> +       op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRSTEN, 8),
> +                       SPI_MEM_OP_NO_DUMMY,
> +                       SPI_MEM_OP_NO_ADDR,
> +                       SPI_MEM_OP_NO_DATA);
> +       spi_nor_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
> +       ret = spi_mem_exec_op(nor->spi, &op);
> +       if (ret) {
> +               dev_warn(nor->dev, "Software reset enable failed: %d\n", ret);
> +               goto out;
> +       }
> +
> +       op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRST, 8),
> +                       SPI_MEM_OP_NO_DUMMY,
> +                       SPI_MEM_OP_NO_ADDR,
> +                       SPI_MEM_OP_NO_DATA);
> +       spi_nor_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
> +       ret = spi_mem_exec_op(nor->spi, &op);
> +       if (ret) {
> +               dev_warn(nor->dev, "Software reset failed: %d\n", ret);
> +               goto out;
> +       }
> +
> +       /*
> +        * Software Reset is not instant, and the delay varies from flash to
> +        * flash. Looking at a few flashes, most range somewhere below 100
> +        * microseconds. So, wait for 200ms just to be sure.
> +        */
> +       udelay(SPI_NOR_SRST_SLEEP_LEN);

Any reference for this delay? I mean datasheet?

Jagan.