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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>
From:   Vignesh Raghavendra <vigneshr@ti.com>
Message-ID: <3e46bc75-6ace-f7c0-1b14-aae812554ac9@ti.com>
Date:   Mon, 7 Jun 2021 12:17:48 +0530
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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.

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