On 12/26/2013 09:56 PM, Matthew Garrett wrote:
On Mon, Dec 16, 2013 at 05:16:39PM -0700, al.stone@xxxxxxxxxx wrote:
+ if (!acpi_gbl_reduced_hardware) {
I don't really understand this. You've explained that runtime hardware
reduced mode switching isn't expected to work, but you're making this
conditional on a runtime flag?
Correct. My apologies if I've made this unclear.
Suppose I build a kernel with full ACPI support. The kernel would
then include legacy and hardware-reduced support. If I pass that
kernel ACPI tables specifying legacy mode, things work fine. If I
pass that same kernel ACPI tables with the hardware-reduced flag
set in the FADT, that should also work -- iff the ACPI driver checks
the acpi_gbl_reduced_hardware flag at run-time. This patch is adding
some of those checks that were missing so that at least the files in
drivers/acpi/*.[ch] are correct; I contend that there are still places
in the drivers/acpi/acpica/*.[ch] files where a Linux driver can call
code it should not be allowed to when in hardware-reduced (e.g., when
using the ACPI global lock [0]). Patching the ACPICA code I'm viewing
as a separate issue yet to be done.
If I build a kernel with only hardware-reduced ACPI support, using
ACPI tables without the hardware-reduced flag set in the FADT will
clearly not work -- nor do I expect it to in this case since most of
the legacy code gets removed at compile time. If the ACPI tables do
have hardware-reduced mode set in the FADT, I expect the kernel to
behave correctly. It may turn out to be exactly the same patch for
ACPICA as mentioned above, but I contend that ACPICA does not
completely handle this case properly at runtime, either.
Does that make sense?
[0] No driver should be doing this but it cannot currently be precluded
by the kernel. You can call me paranoid but I think if it can be
abused by a driver, it will be.
--
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Linaro Enterprise Group
al.stone@xxxxxxxxxx
-----------------------------------
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