linux-kernel - [REGRESSION] firmware: dmi_scan: add SBMIOS entry and DMI tables

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Message-ID: <1459154648.2351.19.camel@users.sourceforge.net>
Date:	Mon, 28 Mar 2016 10:44:09 +0200
From:	Paul Menzel <paulepanter@...rs.sourceforge.net>
To:	Ivan Khoronzhuk <ivan.khoronzhuk@...ballogic.com>,
	Jean Delvare <jdelvare@...e.de>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	coreboot@...eboot.org
Subject: [REGRESSION] firmware: dmi_scan: add SBMIOS entry and DMI tables

Dear Ivan, dear Jeann,

There is an unwanted regression due to commit d7f96f97 (firmware:
dmi_scan: add SBMIOS entry and DMI tables).

Since Linux kernel 4.2 the utility `cbmem`, used to access information
stored in memory, from the coreboot project [1] does not work anymore
on a lot of systems as reported in coreboot’s issue tracker as ticket
#33 [2].

```
Failed to mmap /dev/mem: Resource temporarily unavailable
```

Aaron Durbin analyzed on the coreboot mailing list [3]:

> > 3) Why is that range set as uncached-minus?  Would write-back work?
>
> Please see this thread:
> http://www.coreboot.org/pipermail/coreboot/2015-September/080381.html
>
> The actual issue stems from
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/firmware/dmi_scan.c?id=d7f96f97c4031fa4ffdb7801f9aae23e96170a6f
> which maintains a persistent mapping of smbios tables. It uses
> dmi_remap() which is '#define dmi_remap ioremap' which is where the
> uncached-minus PAT entry comes from. It should be using the same
> mechanism as  the ACPI table mappings which uses ioremap_cache().

It’d be great, if the commit could be reverted, or the code be changed
in a way that `cbmem` still works.

If I should report this issue somewhere else, please tell me too, and
I’ll do my best to follow up there.

Thanks,

Paul

[1] https://www.coreboot.org
[2] https://ticket.coreboot.org/issues/33
[3] https://www.coreboot.org/pipermail/coreboot/2015-October/080568.html
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