Re: [PATCH v2 11/14] mtd: spinand: Perform Power-on-Reset on the flash in mtd_suspend()

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Tue, 12 Oct 2021 02:16:16 +0530
Apurva Nandan <a-nandan@xxxxxx> wrote:

> A soft reset using FFh command doesn't erase the flash's configuration
> and doesn't reset the SPI IO mode also. This can result in the flash
> being in a different SPI IO mode, e.g. Octal DTR, when resuming from
> sleep. This could put the flash in an unrecognized SPI IO mode, making
> it unusable.
> 
> Perform a Power-on-Reset (PoR), if available in the flash, when
> performing mtd_suspend(). This would set the flash to clean
> state for reinitialization during resume and would also ensure that it
> is in standard SPI IO mode (1S-1S-1S) before the resume begins.
> 
> Signed-off-by: Apurva Nandan <a-nandan@xxxxxx>
> ---
>  drivers/mtd/nand/spi/core.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
> index 9b570570ee81..60408531979a 100644
> --- a/drivers/mtd/nand/spi/core.c
> +++ b/drivers/mtd/nand/spi/core.c
> @@ -1316,6 +1316,11 @@ static void spinand_mtd_resume(struct mtd_info *mtd)
>  	int ret;
>  
>  	spinand->reg_proto = SPINAND_SINGLE_STR;
> +	/*
> +	 * PoR Reset (if available by the manufacturer) is performed at the suspend
> +	 * time. Hence, those flashes remain in power-on-state at this point, in a
> +	 * standard SPI IO mode. So, now the core unanimously performs a soft reset.
> +	 */
>  	ret = spinand_reset_op(spinand);
>  	if (ret)
>  		return;
> @@ -1327,6 +1332,21 @@ static void spinand_mtd_resume(struct mtd_info *mtd)
>  	spinand_ecc_enable(spinand, false);
>  }
>  
> +static int spinand_mtd_suspend(struct mtd_info *mtd)
> +{
> +	struct spinand_device *spinand = mtd_to_spinand(mtd);
> +	int ret;
> +
> +	if (!(spinand->flags & SPINAND_HAS_POR_CMD_BIT))
> +		return 0;
> +
> +	ret = spinand_power_on_rst_op(spinand);
> +	if (ret)
> +		dev_err(&spinand->spimem->spi->dev, "suspend() failed\n");
> +
> +	return ret;
> +}

I suspect you need to implement the spi_mem_driver.shutdown() method
and do a PoR in that case too. If the device doesn't support the PoR
command, we should at least switch back to the 1-1-1-STR mode manually.

> +
>  static int spinand_init(struct spinand_device *spinand)
>  {
>  	struct device *dev = &spinand->spimem->spi->dev;
> @@ -1399,6 +1419,7 @@ static int spinand_init(struct spinand_device *spinand)
>  	mtd->_erase = spinand_mtd_erase;
>  	mtd->_max_bad_blocks = nanddev_mtd_max_bad_blocks;
>  	mtd->_resume = spinand_mtd_resume;
> +	mtd->_suspend = spinand_mtd_suspend;
>  
>  	if (nand->ecc.engine) {
>  		ret = mtd_ooblayout_count_freebytes(mtd);