On 2014-10-31 2:02, Mark Rutland wrote: > On Thu, Oct 30, 2014 at 05:52:44PM +0000, Peter Maydell wrote: >> On 30 October 2014 17:43, Alexander Spyridakis >> <a.spyrida...@virtualopensystems.com> wrote: >>> Currently, the virt machine model generates Device Tree information >>> dynamically based on the existing devices in the system. This patch series >>> extends the same concept but for ACPI information instead. A total of seven >>> tables have been >>> implemented in this patch series, which is the minimum for a basic ARM >>> support. >>> >>> The set of generated tables are: >>> - RSDP >>> - XSDT >>> - MADT >>> - GTDT >>> - FADT >>> - FACS >>> - DSDT >>> >>> The tables are created in standalone buffers, taking into account the >>> needed information passed from the virt machine model. When the generation >>> is finalized, the individual buffers are compacted to a single ACPI binary >>> blob, where it is injected on the guest memory space in a fixed location. >>> The guest kernel can find the ACPI tables by providing to it the physical >>> address of the ACPI blob (e.g. acpi_rsdp=0x47000000 boot argument). >> >> (Sorry, I should have waited for the cover letter to arrive before replying.) >> >> I think this is definitely the wrong approach. We already have to >> generate device tree information for the hardware we have, and having >> an equivalent parallel infrastructure for generating ACPI as well >> seems like it would be a tremendous mess. We should support guests >> that require ACPI by having QEMU boot a UEFI bios blob and have that >> UEFI code generate ACPI tables based on the DTB we hand it. >> (Chances seem good that any guest that wants ACPI is going to want >> UEFI runtime services anyway.) > > Depending on why people want ACPI in a guest environment, generating > ACPI tables from a DTB might not be possible (e.g. if they want to use > AML for some reason).
Agreed. > > So the important question is _why_ the guest needs to see an ACPI > environment. What exactly can ACPI provide to the guest that DT does not > already provide, and why is that necessary? What infrastrucutre is > needed for that use case? There is important feature called system device dynamic reconfiguration, you know, hot-add/remove, if a gust need more/less memory or CPU, can we add or remove them dynamically with DT? ACPI can do this, but I have no idea if DT can. (Sorry, I don't know much about DT) Thanks Hanjun
