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

[Pratyush Yadav <p.yadav@ti.com>]

On 21/05/21 09:40PM, Michael Walle wrote:
> 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.

Ok.

> 
> Fixes: 069089acf88b ("mtd: spi-nor: add OTP support")
> Signed-off-by: Michael Walle <michael@walle.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;

I was inclined to say that the loop conditional below would take care of 
this but it can cause an underflow when ofs and len are both 0.

> +
> +	/*
> +	 * 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;
> +	}

Ok.

> +
> +	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);
>  
> +	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;

I wonder if we should have a dev_info() or dev_err() here. I think this 
warrants a dev_dbg() at least.

> +			goto out;
> +		}

So it returns -errno when the check for is_locked() fails and 1 or 0 
when it is locked or not. Ok.

It would be nice if you add a dev_dbg or dev_err() or dev_info() above. 
Nonetheless,

Reviewed-by: Pratyush Yadav <p.yadav@ti.com>

> +	}
> +
>  	*retlen = 0;
>  	while (total_len) {
>  		/*

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.