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 11:56:33 +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 08:47, schrieb Vignesh Raghavendra:
> On 6/7/21 11:38 AM, Michael Walle wrote:
>> 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.
>> 
> 
> Looking further, I don't see the need for 4/5 to be a separate patch.
> Patch 4/5 is simplifying spi_nor_mtd_otp_range_is_locked() by ensuring
> 'len' passed is never 0 which can be done in 3/5 when introducing
> spi_nor_mtd_otp_range_is_locked().
> 
> So why not squashed it into 3/5.

Because, strictly speaking, it is not part of that particular fix
and IMHO violates "It must fix only one thing". But if you're fine
with that, I can squash the two.

TBH I find it kinda funny to bend the rules, just to get rid of
these three lines of code or the ugliness that they will be removed
in the following patch.

-michael