From: Michael Walle <michael@walle.cc>
To: Pratyush Yadav <p.yadav@ti.com>
Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
Tudor Ambarus <tudor.ambarus@microchip.com>,
Miquel Raynal <miquel.raynal@bootlin.com>,
Richard Weinberger <richard@nod.at>,
Vignesh Raghavendra <vigneshr@ti.com>
Subject: Re: [PATCH v4 3/4] mtd: spi-nor: otp: return -EROFS if region is read-only
Date: Wed, 26 May 2021 12:41:36 +0200 [thread overview]
Message-ID: <ca81f21648e55229c8d4533881566471@walle.cc> (raw)
In-Reply-To: <20210525193323.xdvbq3tab6oxk6yh@ti.com>
Am 2021-05-25 21:33, schrieb Pratyush Yadav:
> On 21/05/21 09:40PM, Michael Walle wrote:
>> 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.
>
> Ok.
>
>>
>> Fixes: 069089acf88b ("mtd: spi-nor: add OTP support")
>> Signed-off-by: Michael Walle <michael@walle.cc>
>> ---
>> drivers/mtd/spi-nor/otp.c | 35 +++++++++++++++++++++++++++++++++++
>> 1 file changed, 35 insertions(+)
>>
>> diff --git a/drivers/mtd/spi-nor/otp.c b/drivers/mtd/spi-nor/otp.c
>> index 3898ed67ba1c..b87f96593c13 100644
>> --- a/drivers/mtd/spi-nor/otp.c
>> +++ b/drivers/mtd/spi-nor/otp.c
>> @@ -249,6 +249,31 @@ 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;
>
> I was inclined to say that the loop conditional below would take care
> of
> this but it can cause an underflow when ofs and len are both 0.
Correct. I didn't want to put an extra check to the caller, because
as you noticed, it is checked by the loop there later.
>> +
>> + /*
>> + * If any of the affected OTP regions are locked the entire range is
>> + * considered locked.
>> + */
>> + for (region = spi_nor_otp_offset_to_region(nor, ofs);
>> + region <= spi_nor_otp_offset_to_region(nor, ofs + len - 1);
>> + region++) {
>> + locked = ops->is_locked(nor, region);
>> + if (locked)
>> + return locked;
>> + }
>
> Ok.
Btw I didn't know if I should put a comment here that this if () handles
both locked state and errors. But it seems you've already found out by
looking at the caller ;) I'm not sure if this is obvious, though.
>> +
>> + return 0;
>> +}
>> +
>> static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t
>> ofs,
>> size_t total_len, size_t *retlen,
>> const u8 *buf, bool is_write)
>> @@ -271,6 +296,16 @@ static int spi_nor_mtd_otp_read_write(struct
>> mtd_info *mtd, loff_t ofs,
>> /* don't access beyond the end */
>> total_len = min_t(size_t, total_len, spi_nor_otp_size(nor) - ofs);
>>
>> + if (is_write) {
>> + ret = spi_nor_mtd_otp_range_is_locked(nor, ofs, total_len);
>> + if (ret < 0) {
>> + goto out;
>> + } else if (ret) {
>> + ret = -EROFS;
>
> I wonder if we should have a dev_info() or dev_err() here. I think this
> warrants a dev_dbg() at least.
Are you sure? Reporting something to the user via an error code is
enough IMHO. I wouldn't want my syslog to be cluttered with messages
I already know. I mean the program tell me "hey, you aren't allowed
to write there". Why would the kernel still need to tell me that again?
Without any connection to the caller, I don't get much out of the kernel
message by looking at it alone, just that someone tried to write there.
So definetly no dev_info() or dev_err(). But IMHO no dev_dbg() either.
Tudor, Vingesh, any opinions?
>> + goto out;
>> + }
>
> So it returns -errno when the check for is_locked() fails and 1 or 0
> when it is locked or not. Ok.
>
> It would be nice if you add a dev_dbg or dev_err() or dev_info() above.
> Nonetheless,
>
> Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Thanks for reviewing!
-michael
next prev parent reply other threads:[~2021-05-26 10:41 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-21 19:40 [PATCH v4 0/4] mtd: spi-nor: otp: 4 byte mode fix and erase support Michael Walle
2021-05-21 19:40 ` [PATCH v4 1/4] mtd: spi-nor: otp: fix access to security registers in 4 byte mode Michael Walle
2021-05-31 8:27 ` Tudor.Ambarus
2021-05-21 19:40 ` [PATCH v4 2/4] mtd: spi-nor: otp: use more consistent wording Michael Walle
2021-05-31 8:28 ` Tudor.Ambarus
2021-05-21 19:40 ` [PATCH v4 3/4] mtd: spi-nor: otp: return -EROFS if region is read-only Michael Walle
2021-05-25 19:33 ` Pratyush Yadav
2021-05-26 10:41 ` Michael Walle [this message]
2021-05-26 11:13 ` Pratyush Yadav
2021-05-31 8:52 ` Tudor.Ambarus
2021-06-01 13:02 ` Michael Walle
2021-06-03 5:22 ` Tudor.Ambarus
2021-05-21 19:40 ` [PATCH v4 4/4] mtd: spi-nor: otp: implement erase for Winbond and similar flashes Michael Walle
2021-05-25 19:37 ` Pratyush Yadav
2021-05-31 8:56 ` Tudor.Ambarus
2021-06-01 13:30 ` Michael Walle
2021-06-03 5:08 ` Tudor.Ambarus
2021-06-03 5:30 ` Tudor.Ambarus
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