[flashrom] [PATCH 5/7] warn if SMM BIOS Write Protection is detected in BIOS_CNTL

[Stefan Reinauer]

* Stefan Tauner <stefan.tauner at student.tuwien.ac.at> [111103 12:04]:
> > > -	new = old | 1;
> > > +	/*
> > > +	 * Quote from the 6 Series datasheet:
> > > +	 * "5: SMM BIOS Write Protect Disable (SMM_BWP)
> > > +	 * 1 = BIOS region SMM protection is enabled.
> > > +	 * The BIOS Region is not writable unless all processors are in SMM."
> > > +	 * In earlier chipsets this bit is reserved. */
> > > +	if (old&  (5<<  1)) {
> > > +		msg_pinfo("WARNING: BIOS region SMM protection is enabled!\n");
> > > +		return -1;
> > You might still be successful doing the write, in case the SMM handler 
> > does not enforce the protection, so maybe you should just print a 
> > warning but not return here?
> 
> in chromium-os you are trying to unset that bit[1], but according to the
> data sheet this is impossible - it is R/W LO (read/write lock once).

Maybe there is some confusion about R/W LO. The bit can be locked, but
that does not mean it is locked automatically by writing / clearing it.
Once it is locked, the lock can not be undone except by a chipset reset.

> and you degraded the warning to dbg level... certainly not suited for
> upstream, but maybe desirable for chromium(?).

Yes, that was done on purpose, because the lock bit that prevents the
bit from being cleared also produces a warning.

> have you tested this on a board where SMM_BWP is really set to 1? we
> may wanna try to write it anyway, but it would be far more interesting
> if it really works on some chipsets :)

Yes, this was implemented to fix a problem I was seeing, and it solved
the problem. :-)

Stefan