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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>, <Tudor.Ambarus@microchip.com>
CC:     <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>
From:   Vignesh Raghavendra <vigneshr@ti.com>
Message-ID: <1549db61-500a-e5df-9303-823b41457861@ti.com>
Date:   Mon, 7 Jun 2021 11:16:07 +0530
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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?

Regards
Vignesh