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Subject: Re: [PATCH v5 3/5] mtd: spi-nor: otp: return -EROFS if region is
 read-only
To:     Michael Walle <michael@walle.cc>
CC:     <Tudor.Ambarus@microchip.com>, <linux-mtd@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <p.yadav@ti.com>,
        <miquel.raynal@bootlin.com>, <richard@nod.at>
References: <20210604100252.9975-1-michael@walle.cc>
 <20210604100252.9975-4-michael@walle.cc>
 <c2b58dcc-5a60-792c-30ac-a3db327a85ed@microchip.com>
 <e117bc50b9f9e10549c25602b66cfe26@walle.cc>
 <1549db61-500a-e5df-9303-823b41457861@ti.com>
 <4ba7994b0cc8d436012a776ca14addca@walle.cc>
 <3e46bc75-6ace-f7c0-1b14-aae812554ac9@ti.com>
 <2559d150b3a0d964ece0c9e29e155ecc@walle.cc>
From:   Vignesh Raghavendra <vigneshr@ti.com>
Message-ID: <4b3e1bde-09ff-eebd-8e93-8db7a5834f96@ti.com>
Date:   Mon, 7 Jun 2021 16:00:34 +0530
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On 6/7/21 3:26 PM, Michael Walle wrote:
> 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@microchip.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@walle.cc>
>>>>>>> Reviewed-by: Pratyush Yadav <p.yadav@ti.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.
> 

This is still fixing only one thing "Indicating OTP writes are ignored
when region is locked" (ie spi_nor_mtd_otp_range_is_locked() check).
But, spi_nor_mtd_otp_range_is_locked() (as in 3/5) can be simplified if
'len != 0' is checked prior to calling the function. That's what 4/5
does which I believe can be squashed here.

I just don't like code being refactored for the purpose of being able to
be backported. It feels weird to have a piece of code being added in one
commit, and then being deleted the very next commit.
So strictly speaking 4/5 has to come before 3/5.

But I am fine to live with this temporary ugliness if Tudor agrees.


Regards
Vignesh