linux-kernel - Re: [PATCH v4 3/4] mtd: spi-nor: otp: return -EROFS if region is read-only

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Message-ID: <d4b4d8c5-aacc-0cb7-2d30-8480b7904ac6@microchip.com>
Date:   Thu, 3 Jun 2021 05:22:55 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <michael@...le.cc>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     <p.yadav@...com>, <miquel.raynal@...tlin.com>, <richard@....at>,
        <vigneshr@...com>
Subject: Re: [PATCH v4 3/4] mtd: spi-nor: otp: return -EROFS if region is
 read-only

On 5/21/21 10:40 PM, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> SPI NOR flashes will just ignore program commands if the OTP region is
> locked. Thus, a user might not notice that the intended write didn't end
> up in the flash. Return -EROFS to the user in this case. From what I can
> tell, chips/cfi_cmdset_0001.c also return this error code.
> 
> One could optimize spi_nor_mtd_otp_range_is_locked() to read the status
> register only once and not for every OTP region, but for that we would
> need some more invasive changes. Given that this is
> one-time-programmable memory and the normal access mode is reading, we
> just live with the small overhead.
> 
> Fixes: 069089acf88b ("mtd: spi-nor: add OTP support")
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>  drivers/mtd/spi-nor/otp.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/otp.c b/drivers/mtd/spi-nor/otp.c
> index 3898ed67ba1c..b87f96593c13 100644
> --- a/drivers/mtd/spi-nor/otp.c
> +++ b/drivers/mtd/spi-nor/otp.c
> @@ -249,6 +249,31 @@ static int spi_nor_mtd_otp_info(struct mtd_info *mtd, size_t len,
>         return ret;
>  }
> 
> +static int spi_nor_mtd_otp_range_is_locked(struct spi_nor *nor, loff_t ofs,
> +                                          size_t len)
> +{
> +       const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
> +       unsigned int region;
> +       int locked;
> +
> +       if (!len)
> +               return 0;

meh

> +
> +       /*
> +        * If any of the affected OTP regions are locked the entire range is
> +        * considered locked.
> +        */
> +       for (region = spi_nor_otp_offset_to_region(nor, ofs);
> +            region <= spi_nor_otp_offset_to_region(nor, ofs + len - 1);
> +            region++) {
> +               locked = ops->is_locked(nor, region);
> +               if (locked)
> +                       return locked;
> +       }
> +
> +       return 0;
> +}
> +
>  static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
>                                       size_t total_len, size_t *retlen,
>                                       const u8 *buf, bool is_write)
> @@ -271,6 +296,16 @@ static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
>         /* don't access beyond the end */
>         total_len = min_t(size_t, total_len, spi_nor_otp_size(nor) - ofs);

can we move the total_len computation before calling spi_nor_lock_and_prep(),
and just return 0 if total_len is zero? It will return early, avoiding unnecessary
steps.

> 
> +       if (is_write) {
> +               ret = spi_nor_mtd_otp_range_is_locked(nor, ofs, total_len);
> +               if (ret < 0) {
> +                       goto out;
> +               } else if (ret) {
> +                       ret = -EROFS;
> +                       goto out;
> +               }
> +       }
> +
>         *retlen = 0;
>         while (total_len) {
>                 /*
> --
> 2.20.1
>