From: Pratyush Yadav <p.yadav@ti.com>
To: Michael Walle <michael@walle.cc>
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 16:43:35 +0530 [thread overview]
Message-ID: <20210526111333.suxmmtkngqeyuz62@ti.com> (raw)
In-Reply-To: <ca81f21648e55229c8d4533881566471@walle.cc>
On 26/05/21 12:41PM, Michael Walle wrote:
> 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.
I didn't catch this on the first read. I only figured it out when I
looked at the return check below. So it is certainly not obvious.
>
> > > +
> > > + 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?
Either is fine by me.
>
>
> > > + 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
--
Regards,
Pratyush Yadav
Texas Instruments Inc.
next prev parent reply other threads:[~2021-05-26 11:13 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
2021-05-26 11:13 ` Pratyush Yadav [this message]
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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