linux-kernel - Re: [PATCH v6 5/5] mtd: spi-nor: keep lock bits if they are non-volatile

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Date:   Wed, 02 Dec 2020 12:25:49 +0100
From:   Michael Walle <michael@...le.cc>
To:     Tudor.Ambarus@...rochip.com
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        boris.brezillon@...labora.com
Subject: Re: [PATCH v6 5/5] mtd: spi-nor: keep lock bits if they are
 non-volatile

Am 2020-12-02 12:10, schrieb Tudor.Ambarus@...rochip.com:
> On 11/30/20 4:38 PM, Michael Walle wrote:
[..]
>>>> +        * indicated by SNOR_F_WP_IS_VOLATILE.
>>>> +        */
>>>> +       if (IS_ENABLED(CONFIG_MTD_SPI_NOR_WP_DISABLE) ||
>>>> +           (IS_ENABLED(CONFIG_MTD_SPI_NOR_WP_DISABLE_ON_VOLATILE) 
>>>> &&
>>>> +            nor->flags & SNOR_F_WP_IS_VOLATILE)) {
>>>> +               err = spi_nor_unlock_all(nor);
>>>> +               if (err) {
>>>> +                       dev_err(nor->dev, "Failed to unlock the 
>>>> entire
>>>> flash memory array\n");
>>> 
>>> dev_dbg for low level info
>> 
>> Is this low level info or an actual error? Which raises the question:
>> should spi_nor_unlock_all() in case SWRD couldn't be cleared and thus
>> should all the spi_nor_init fail of this? Or should it rather be a
> 
> yes, it should, because the flash will not work as expected/requested.

One counterargument: take our sl28 board, it has a hardware 
write-protected
SPI flash. It actually works right now because the write_sr_and_check()
doesn't work as intended and doesn't check what is written. So if you'd
fix that (and these changes would be backported to the stable trees), 
you'd
basically break spi-nor on these boards. And this _must_ be the case for
all boards which are actually using (hard- or sofware) write-protection.
That is the only way write-protection makes sense prior to this patch
series. Because linux will happily unlock every flash on startup. 
Therefore,
the hardware write protection is the only measure against this.

-michael