Re: [RFC PATCH 2/8] mtd: rawnand: ams-delta: Write protect device during probe

Boris Brezillon
2018-07-19T06:22:07Z

On Thu, 19 Jul 2018 01:57:04 +0200
Janusz Krzysztofik <jmkrzyszt@gmail.com> wrote:

> Initialize NWP GPIO pin low to protect the device from hazard during
> probe. Release write protection as soon as the device is under
> control.
>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
> ---
> drivers/mtd/nand/raw/ams-delta.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mtd/nand/raw/ams-delta.c b/drivers/mtd/nand/raw/ams-delta.c
> index 48233d638d2a..6ac38e9cfa1a 100644
> --- a/drivers/mtd/nand/raw/ams-delta.c
> +++ b/drivers/mtd/nand/raw/ams-delta.c
> @@ -219,8 +219,8 @@ static int ams_delta_init(struct platform_device *pdev)
>
> platform_set_drvdata(pdev, priv);
>
> - /* Set chip enabled, but */
> - priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_HIGH);
> + /* Set chip enabled but write protected */
> + priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_LOW);
> if (IS_ERR(priv->gpiod_nwp)) {
> err = PTR_ERR(priv->gpiod_nwp);
> dev_err(&pdev->dev, "NWP GPIO request failed (%d)\n", err);
> @@ -267,6 +267,9 @@ static int ams_delta_init(struct platform_device *pdev)
> if (err)
> goto out_mtd;
>
> + /* As soon as the device is found, release write protection */
> + gpiod_set_value(priv->gpiod_nwp, 1);

Please don't do that until we have a generic way to assert/deassert WP
from the core. I agree that we shouldn't write things in the
nand_scan() path, but I'd be more comfortable if the core had control
on this pin just in case we ever need to disable write-protection
during chip detection/initialization.

> +
> /* Register the partitions */
> mtd_device_register(mtd, partition_info, ARRAY_SIZE(partition_info));
>
> @@ -288,6 +291,9 @@ static int ams_delta_cleanup(struct platform_device *pdev)
> struct mtd_info *mtd = nand_to_mtd(&priv->nand_chip);
> void __iomem *io_base = priv->io_base;
>
> + /* Apply write protection */
> + gpiod_set_value(priv->gpiod_nwp, 0);
> +
> /* Release resources, unregister device */
> nand_release(mtd);
>