On Tue, 2014-05-13 at 04:54 +0200, Laszlo Ersek wrote: > > But, second, we've known for quite some time that windows server 2008 r2 > works well with the SeaBIOS CSM and a few edk2 patches (thanks again to > David Woodhouse and Kevin O'Connor). > > There are two problems with the CSM, one specific (and possibly > accidental/fixable), and one generic (and inherent). > > - The specific (possibly accidental, fixable) problem is that using the > SeaBIOS CSM plus the CSM infrastructure in edk2 breaks OVMF's S3 resume. > I had not set out to track this down because of the other problem (see > below).
Wimp :) > - The generic / inherent problem with the current SeaBIOS CSM + the edk2 > CSM infrastructure is that the combination is a nightmare to trace, > debug, and modify, for mere mortals. It switches from long mode to real > mode and vice versa, and it's impossible to follow unless you know the > relevant magic from the Intel SDM from memory. Actually I'm not sure that's any more true for CSM than it is for EDK2 itself. If it doesn't work, most mortals will just give up. You did a *lot* of amazing work on enabling S3 support in OVMF. That was dark magic, and yes its interaction with CSM will also involve darker magic. But once it's fixed, it's fixed. It's largely a solved problem and shouldn't *need* to be re-debugged very often. Especially since 'git bisect' is such a no-brainer to use once you at least have a point in history that *did* work¹. > ... > (Without enabling the CSM in an OVMF build, the option to legacy-boot is > lost of course as well, but I expressly don't desire that option. Just > boot legacy OSes with pure SeaBIOS; it's easy to choose your firmware in > a virtual machine.) I don't think I agree that it's easy to choose your firmware. If I'm using virt-manager/libvirt under Fedora, how do I do it? I suppose it'd be implicit in my choice of operating system? So I might be expected to know that selecting "Fedora 20" will use legacy BIOS while "Fedora 21" will magically switch me over to UEFI, according to criteria that are entirely opaque to me? And if I'm using Ubuntu or something else, the choices there might be entirely different? Or were you really intending the tools to give the user an explicit choice of legacy vs. UEFI rather than depending on the OS? That would kind of suck too. Really, I think we should make CSM work and keep it working, then it's a no-brainer for users because things Just Work™. Never underestimate the collective stupidity of end-users. If we can make it Just Work™, especially since we're so close already, then I think we should. Which is why I spent the time to enable CSM in the first place, of course. Not to mention the fact that having OVMF+CSM as a default firmware will serve to accelerate adoption of UEFI in virtual machines, and that gives people a *really* easy playground to get involved in EDK2 source code; fixing bugs and making improvements. -- David Woodhouse Open Source Technology Centre david.woodho...@intel.com Intel Corporation ¹ Assuming everyone is using git properly and there are never any large code dumps labelled "merge from foobar SVN" of course. Anyone doing *that* should have their commit privs revoked until they've retaken the "source code management 101" course. Or sobered up.
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