Re: [PATCH 2/2] mtd: core: Don't fail mtd_device_parse_register() if OTP is unsupported

[Michael Walle]

Hi,

On Mon Mar 11, 2024 at 5:20 PM CET, Aapo Vienamo wrote:
> On Mon, Mar 11, 2024 at 03:38:17PM +0100, Michael Walle wrote:
> > On Thu Mar 7, 2024 at 2:04 PM CET, Aapo Vienamo wrote:
> > > Handle the case where -EOPNOTSUPP is returned from OTP driver.
> > > +	/*
> > > +	 * Don't abort MTD init if OTP functionality is unsupported. The
> > > +	 * cleanup of the OTP init is contained within mtd_otp_nvmem_add().
> > > +	 * Omitting goto out here is safe since the cleanup code there
> > > +	 * should be no-ops.
> > > +	 */
> > 
> > Only if that's true for both the factory and user OTP area.
>
> I'm not sure I follow. I'm not seeing a path in mtd_otp_nvmem_add()
> that would result in either mtd->otp_user_nvmem or mtd->otp_factor_nvmem
> needing to be cleaned up by the caller, if an error is returned, if
> that's what you are referring to.

Yes you're right, sorry for the noise.
>
> > Also, you'll print an error message for EOPNOTSUPP, although that is
> > not really an error. Is that intended? 
>
> Well, when we hit this, the functionality of the SPI memory itself is
> degraded in the sense that the OTP functionality is not available. What
> would you suggest?

But it's not really an error, I mean, we are ignoring that one on
purpose now :) I'd just guard it with "if (ret != -EOPNOTSUPP)".

> > 
> > >  	ret = mtd_otp_nvmem_add(mtd);
> > > -	if (ret)
> > > +	if (ret && ret != -EOPNOTSUPP)
> > 
> > Maybe there is a better way to handle this, like controller
> > capabilities instead of putting these EOPNOTSUPP checks
> > everywhere? I'm not sure.
>
> Trying to come up with clear semantics for a capabilities flag to solve
> this is difficult. The issue is that on the SPI controller side, the
> limitation stems from the really strict set of opcodes that are allowed.
> For example, we already hit an error with the 0x35 (read configuration
> register) not being on the set of allowed opcodes. While this
> instruction is used by the OTP code, it's not a strictly OTP specific
> operation.

I see. It's just that due to this (very) restricted SPI contoller
all this EOPNOTSUPP handling is creeping into more an more places in
spi-nor core and now mtdcore :)

Anyway, I don't have any better idea right now. So I think this is
fine.

-michael


> If there was a flag that would signal OTP support, I think it would have
> be defined as "the controller supports all operations that are
> performed by the OTP code", which sounds brittle. The other way around
> would be to have a really fine-grained set of flags that the MTD core
> would check, but that feels tedious and error prone as well.

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