On Wed, May 08, 2013 at 12:31:50PM +0300, Gleb Natapov wrote: > On Tue, May 07, 2013 at 07:01:13PM -0400, Kevin O'Connor wrote: > > On Tue, May 07, 2013 at 09:00:48PM +0300, Michael S. Tsirkin wrote: > > > On Thu, Apr 25, 2013 at 12:02:20PM +0300, Michael S. Tsirkin wrote: > > > > Untested yet, but I thought I'd share the > > > > BIOS bits so we can agree on direction. > > > > > > > > In particular check out ROM sizes: > > > > - Before patchset with DSDT enabled > > > > Total size: 127880 Fixed: 59060 Free: 3192 (used 97.6% of 128KiB > > > > rom) > > > > - Before patchset with DSDT disabled > > > > Total size: 122844 Fixed: 58884 Free: 8228 (used 93.7% of 128KiB > > > > rom) > > > > - After patchset: > > > > Total size: 128776 Fixed: 59100 Free: 2296 (used 98.2% of 128KiB > > > > rom) > > > > - Legacy disabled at build time: > > > > Total size: 119836 Fixed: 58996 Free: 11236 (used 91.4% of 128KiB > > > > rom) > > > > > > > > As can be seen from this, most size savings come > > > > from dropping DSDT, but we do save a bit by removing > > > > other tables. Of course the real reason to move tables to QEMU > > > > is so that ACPI can better match hardware. > > > > > > > > This patchset adds an option to move all code for formatting acpi tables > > > > out of BIOS. With this, QEMU has full control over the table layout. > > > > All tables are loaded from the new "/etc/acpi/" directory. > > > > Any entries in this directory cause BIOS to disable > > > > ACPI table generation completely. > > > > A generic linker script, controlled by QEMU, is > > > > loaded from "/etc/linker-script". It is used to > > > > patch in table pointers and checksums. > > > > > > After some thought, there are two additional > > > options worth considering, in that they simplify > > > bios code somewhat: > > > > > > - bios could get size from qemu, allocate a buffer > > > (e.g. could be one buffer for all tables) > > > and pass the address to qemu. > > > qemu does all the patching > > > > > > - further, qemu could do the copy of tables into > > > that address directly > > > > This seems more complex than necessary to me. > > > > The important task is to get the tables generated in QEMU - I'd focus > > on getting the tables generated in QEMU (one table per fw_cfg "file"). > > Once that is done, the SeaBIOS side can be easily implemented, and we > > can add any enhancements on top if we feel it is necessary. > > > +1. This "copy of tables into that address directly" is just an ad-hoc PV > isa DMA device in disguise. Such device was refused when libguestfs > asked for it, and they wanted it for much better reason - performance. > There is existing mechanism to pass data into firmware. Use it please.
Yes I can code it up using FW_CFG for now. One issue with QEMU_CFG_FILE_DIR is that it's broken wrt migration, unless we pass in very small bits of data which we can guarantee never changes across qemu versions. Off-list, I suggested fixing it and migrating file content, but Anthony thinks it's a bad idea. I don't care much. > -- > Gleb.
