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]:
- 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/driver... 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