I looked at my DSDT myself, and compared it to the DSDT on my laptop (which runs Genode without any problems). The _PRT method is very similar, but the _PIC method is very different. I don't fully understand what's going on, but it calls a method IRQC(), which sets a bunch of variables (PIRA, PIRB, PIRC, PIRD, PIRE, PIRF, PIRG, PIRH, HDAD, GEC, GPP0, GPP1, GPP2, GPP3, USB1, USB2, USB3, USB4, USB5, USB6, USB7, IDE, SATA) to 0x1F. It also sets Local1 = PD64. After returning from IRQC(), _PIC() sets PICM = Arg0.

To better make sense of this, I need to know how Genode currently sets the interrupt model (PIC, APIC, or SAPIC). The ACPI specification requires PIC mode unless _PIC is called. How does Genode get around that?

On Thu, Apr 5, 2018 at 1:43 AM, Christian Helmuth <christian.helmuth@...495...labs.com> wrote:
Hello Ben,

On Wed, Apr 04, 2018 at 01:23:42PM -0600, Nobody III wrote:
> Thanks for the analysis. The OSDev wiki says, "The ACPICA code is meant to
> be directly integrated into the host OS, as a kernel-resident subsystem."
> This suggests that we could likely use acpica without too much trouble.

That's perfectly true for traditional monolithic kernels like Linux
but should not be taken as given for our approach of a minimal trusted
computing base. ACPI comes with significant complexity due to its
dependency on AML and therefore an AML interpreter. If there's the
slightest chance to keep ACPICA out of the TCB we should invest the
effort. A good example is our acpi_drv which implements the ATARE
approach [2] to statically parse PCI routing tables.

> By the way, could you please give me a quick explanation of the _PIC and
> _PRT methods, and how they're stored?

Please refer to the ACPI specification [1] sections "5.8.1 _PIC
Method" and "6.2.13 _PRT (PCI Routing Table)". Those methods are part
of the DSDT table and implemented in ASL/AML.

[1] http://www.uefi.org/sites/default/files/resources/ACPI%206_2_A_Sept29.pdf
[2] https://os.inf.tu-dresden.de/papers_ps/tr-atare-2009.pdf

Regards
--
Christian Helmuth
Genode Labs

https://www.genode-labs.com/ · https://genode.org/
https://twitter.com/GenodeLabs · /ˈdʒiː.nəʊd/

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth

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