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

From: Paul Menzel
Date: Mon Mar 28 2016 - 05:28:49 EST

Dear Ivan, dear Jeann,

There is an unwanted regression due to commitÂd7f96f97 (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 corebootâs 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?ÂÂWould 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 asÂÂthe ACPI table mappings which uses ioremap_cache().

Itâd 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
Iâll do my best to follow up there.




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