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Re: [Xen-devel] [PATCH] [HVM] [TPM] [1/3] Add TPM TIS type of device toACPI device list

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 10/27/2006 12:57:52 PM:

> On 27/10/06 6:02 pm, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

> To solve this we would need one of the following
> - a BIOS that probes for such devices and dynamically appends the
> info to the (static) ACPI tables
> - a tool that builds and compiles the ACPI tables according to the
> desired configuration of the HVM VM before the HVM is started
> A later version (2.6.18) of the corresponding Linux driver allows
> you to modprobe the module with a '-force' parameter for platforms
> where the correct ACPI information is not available. [In that case
> if the vTPM facility is not available, the /dev/tpm0 won't become available.]
> I am not sure what the right solution is.

> I think your above proposed solution is correct: either dynamically
> append info to a static spartan ACPI table, or dynamically trim down
> a static ‘christmas tree’ ACPI table. Probably the former is best,
> and done in hvmloader.

I am unforunately not an expert on ACPI tables...
Currently the device is part of the DSDT table. Appending this device's entry to it would probably be possible since in the whole compiled ACPI table layout the DSDT is included as the last part and therefore there should be available unused memory after that. To implement this it would require an ACPI DSDT table parser, to change the length of the table and its checksum and if I interpret the diff of the hexadecimal array of the compiled acpi table correctly, other places as well.
Now if I don't want to change that DSDT table, what type of table would it have to create where I can put this device into? Where do I connect this table to?

Would another possibility be to disable or overwrite the existing device entry in the static table if the hvmloader's probing does not find the device?


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