linux-kernel - Re: [PATCH v5 3/5] mtd: spi-nor: otp: return -EROFS if region is read-only

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Date:   Mon, 07 Jun 2021 08:08:56 +0200
From:   Michael Walle <michael@...le.cc>
To:     Vignesh Raghavendra <vigneshr@...com>
Cc:     Tudor.Ambarus@...rochip.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, p.yadav@...com,
        miquel.raynal@...tlin.com, richard@....at
Subject: Re: [PATCH v5 3/5] mtd: spi-nor: otp: return -EROFS if region is
 read-only

Am 2021-06-07 07:46, schrieb Vignesh Raghavendra:
> On 6/4/21 6:45 PM, Michael Walle wrote:
>> Am 2021-06-04 15:07, schrieb Tudor.Ambarus@...rochip.com:
>>> On 6/4/21 1:02 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>
>>>> Reviewed-by: Pratyush Yadav <p.yadav@...com>
>>>> ---
>>>>  drivers/mtd/spi-nor/otp.c | 36 ++++++++++++++++++++++++++++++++++++
>>>>  1 file changed, 36 insertions(+)
>>>> 
>>>> diff --git a/drivers/mtd/spi-nor/otp.c b/drivers/mtd/spi-nor/otp.c
>>>> index 3898ed67ba1c..063f8fb68649 100644
>>>> --- a/drivers/mtd/spi-nor/otp.c
>>>> +++ b/drivers/mtd/spi-nor/otp.c
>>>> @@ -249,6 +249,32 @@ 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;
>>>> +
>>> 
>>> You won't need this if you put patch 4/5 before this one. With this:
>> 
>> This patch will get backported to the stable kernels. Patch 4 on the
>> other hand does not.
>> 
> 
> I don't see why 4/5 cannot be marked for backport too as it makes 3/5
> much cleaner?

What kind of problem does 4/5 fix? I can't see how that patch would
apply to any rule in Documentation/process/stable-kernel-rules.rst.

But sure, adding the same Fixes: tag, I can swap those two.

-michael