linux-kernel - Re: [PATCH 2/3] watchdog: hpwdt: SMBIOS check

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Message-ID: <20171022015621.GB28641@anatevka.americas.hpqcorp.net>
Date:   Sat, 21 Oct 2017 19:56:21 -0600
From:   Jerry Hoemann <jerry.hoemann@....com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     wim@...ana.be, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jerry Hoemann <jerry.hoemann@....com>
Subject: Re: [PATCH 2/3] watchdog: hpwdt: SMBIOS check

On Fri, Oct 20, 2017 at 07:37:21PM -0700, Guenter Roeck wrote:
> On 10/20/2017 03:54 PM, Jerry Hoemann wrote:
> > Correct test on SMBIOS table 219 Misc Features bits for UEFI supported.
> > 
> Please explain in more detail. There is no table 219 in the SMBIOS specification.

Sorry, my patch documentation was imprecise, I should have stated Type 219 record.

Type 219 is an HPE OEM SMBIOS extension whose contents are considered
confidential, so I'm not at liberty to go into details.  I will say
that Type 219 describes features of the iLO which hpwdt is implemented
against.

> There is table 9, BIOS Characteristics Extension Byte 2, which specifies bit 3
> as "UEFI Specification is supported.", but nothing that really maps to the
> other byte, and no "misc features". Maybe this is HP specific, but then we'll
> need to have much better explanation.

This patch is to correct commit cce78da766.

Our current servers do not support the CRU BIOS interfaces and we
need to avoid calling it.  Tom initially only checked that iCRU which
replaced CRU was supported.  But, later added code to extend to also
test whether UEFI was supported to anticipate a time when iCRU wasn't
supported either but where we still don't want to call back into CRU.

Tom's original change was implemented to an older definition of Type 219.
Unfortunately, the specification (and firmware) were modified to use a
different pair of bits to represent UEFI.  However, a corresponding change
to update Linux was missed.

The code is currently working today as the iCRU bit is correctly being
checked.  But as the purpose of cce78da766 is to protect the
code for a time when iCRU isn't true, we want to correct the
checking of the UEFI bit.

> 
> > Signed-off-by: Jerry Hoemann <jerry.hoemann@....com>
> > ---
> >   drivers/watchdog/hpwdt.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
> > index ef54b03..4c011e8 100644
> > --- a/drivers/watchdog/hpwdt.c
> > +++ b/drivers/watchdog/hpwdt.c
> > @@ -707,7 +707,7 @@ static void dmi_find_icru(const struct dmi_header *dm, void *dummy)
> >   		smbios_proliant_ptr = (struct smbios_proliant_info *) dm;
> >   		if (smbios_proliant_ptr->misc_features & 0x01)
> >   			is_icru = 1;
> > -		if (smbios_proliant_ptr->misc_features & 0x408)
> > +		if (smbios_proliant_ptr->misc_features & 0x1400)
> >   			is_uefi = 1;
> >   	}
> >   }
> > 
> Presumably patch 2/3 and 3/3 are bug fixs and should come first
> so they can be applied to stable releases.
> 

I can re-order the patches or delay the first patch if necessary.

Thanks
Jerry

-- 

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Jerry Hoemann                  Software Engineer   Hewlett Packard Enterprise
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