Re: [PATCH] mtd: core: handle flashes without OTP gracefully

[Guenter Roeck]

On 7/6/21 9:29 AM, Miquel Raynal wrote:
> Hi Guenter,
>
> Guenter Roeck <linux@xxxxxxxxxxxx> wrote on Sat, 3 Jul 2021 10:26:06
> -0700:
>
> > On 7/3/21 9:42 AM, Tudor.Ambarus@xxxxxxxxxxxxx wrote:
> > > On 7/3/21 7:08 PM, Michael Walle wrote:
> > > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > > >
> > > > Am 3. Juli 2021 11:56:14 MESZ schrieb Tudor.Ambarus@xxxxxxxxxxxxx:
> > > > > On 7/2/21 12:38 PM, Michael Walle wrote:
> > > > > > EXTERNAL EMAIL: Do not click links or open attachments unless you
> > > > > know the content is safe
> > > > > > There are flash drivers which registers the OTP callbacks although
> > > > > the
> > > > > > flash doesn't support OTP regions and return -ENODATA for these
> > > > > > callbacks if there is no OTP. If this happens, the probe of the whole
> > > > >
> > > > > why do they register the OTP callback if they don't support OTP?
> > > >
> > > > I don't know. But I certainly won't touch that code :p
> > >
> > > why? :D
> > >    
> > > >   
> > > > > > flash will fail. Fix it by handling the ENODATA return code and skip
> > > > > > the OTP region nvmem setup.
> > > > > >
> > > > > > Fixes: 4b361cfa8624 ("mtd: core: add OTP nvmem provider support")
> > > > > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > > > Signed-off-by: Michael Walle <michael@xxxxxxxx>
> > > > > > ---
> > > > > >    drivers/mtd/mtdcore.c | 10 ++++++++--
> > > > > >    1 file changed, 8 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> > > > > > index b5ccd3037788..6881d1423dd6 100644
> > > > > > --- a/drivers/mtd/mtdcore.c
> > > > > > +++ b/drivers/mtd/mtdcore.c
> > > > > > @@ -880,7 +880,10 @@ static int mtd_otp_nvmem_add(struct mtd_info
> > > > > *mtd)
> > > > > >           if (mtd->_get_user_prot_info && mtd->_read_user_prot_reg) {
> > > > > >                   size = mtd_otp_size(mtd, true);
> > > > > > -               if (size < 0)
> > > > > > +               /* ENODATA means there is no OTP region */
> > > > > > +               if (size == -ENODATA)
> > > > >
> > > > > If no OTP data, maybe it's more appropriate for the clients to just
> > > > > return a retlen of 0.
> > > >
> > > > you mean already checking ENODATA in mtd_otp_size() and return 0. That would also make the hunk below unnecessary. I'll change it.
> > >
> > > I've thought about:
> > >
> > > diff --git a/drivers/mtd/chips/cfi_cmdset_0001.c b/drivers/mtd/chips/cfi_cmdset_0001.c
> > > index 54f92d09d9cf..9419b33d7238 100644
> > > --- a/drivers/mtd/chips/cfi_cmdset_0001.c
> > > +++ b/drivers/mtd/chips/cfi_cmdset_0001.c
> > > @@ -2314,7 +2314,7 @@ static int cfi_intelext_otp_walk(struct mtd_info *mtd, loff_t from, size_t len,
> > >    >          /* Check that we actually have some OTP registers */
> > >           if (!extp || !(extp->FeatureSupport & 64) || !extp->NumProtectionFields)
> > > -               return -ENODATA;
> > > +               return 0;
> > >    
> >
> > There are various places where this is called, including code returning information
> > to userspace. That means you'd be changing the ABI to userspace which would now suddenly
> > return 0 instead of -ENODATA.
>
> Yeah let's avoid this if possible, even though I liked Tudor's approach.
>
> Would Michael proposal of checking it in mtd_otp_size() still affect
> userspace? If not, having a single check over the -ENODATA return code
> seems attractive.

The check in mtd_otp_nvmem_add() does not affect userspace.

Guenter