On Fri, 2013-08-23 at 21:21 +0300, Ville Syrjälä wrote: > On Tue, Aug 20, 2013 at 10:46:45PM +0300, Ville Syrjälä wrote: > > On Fri, Aug 16, 2013 at 12:22:14PM -0600, Alex Williamson wrote: > > > On Fri, 2013-08-16 at 13:20 +0300, Ville Syrjälä wrote: > > > > On Thu, Aug 15, 2013 at 04:54:15PM -0600, Alex Williamson wrote: > > > > > On Fri, 2013-08-16 at 08:49 +1000, Dave Airlie wrote: > > > > > > On Fri, Aug 16, 2013 at 8:43 AM, Alex Williamson > > > > > > <alex.williamson@xxxxxxxxxx> wrote: > > > > > > > This is intended to add VGA arbiter support for Intel HD graphics on > > > > > > > Core processors. The old GMCH registers no longer exist, so even > > > > > > > though it appears that i915 participates in VGA arbitration, it doesn't > > > > > > > work. On Intel HD graphics we already attempt to disable VGA regions > > > > > > > of the device. This makes registering as a VGA client unnecessary since > > > > > > > we don't intend to operate differently depending on how many VGA devices > > > > > > > are present. We can disable VGA memory regions by clearing a memory > > > > > > > enable bit in the VGA MSR. That only leaves VGA IO, which we update > > > > > > > the VGA arbiter to know that we don't participate in VGA memory > > > > > > > arbitration. We also add a hook on unload to re-enable memory and > > > > > > > reinstate VGA memory arbitration. > > > > > > > > > > > > I would think there is still a VGA disable bit on the Intel device > > > > > > somewhere, we'd just need > > > > > > Intel to look in the docs and find it. A bit that can nuke both i/o > > > > > > and cmd regs. > > > > > > > > > > The only bit available is in the GGC and is a keyed/locked register that > > > > > not only disables VGA memory and I/O, but also modifies the class code > > > > > of the device. Early Core processors didn't lock this, but it's > > > > > untouchable in newer ones AFAICT. Thanks, > > > > > > > > I've not found anything else in the docs. And also we _need_ VGA I/O > > > > access to make i915_disable_vga() work. It's not 100% clear whether > > > > we really need to poke at the sequencer register in modern hardware, > > > > but the docs do still list it as a mandatory step. So even if we were > > > > to have a global "disable VGA I/O and mem bit" we'd need to make sure > > > > we already disabled VGA eg. after resume when the BIOS had a chance to > > > > turn the VGA display back on. I think there were also some BIOSen that > > > > turned VGA display back on when closing/opening the laptop lid. Not > > > > sure what would even happen with those if totally disabled VGA I/O > > > > access. I'm not sure they actually frob with the VGA regs though. > > > > Could be they just turn on the VGA display bit in the VGA_CONTROL > > > > register. > > > > > > Hmm, it appears the MSR write isn't fully disabling VGA memory space. > > > When the VBIOS for the PEG graphics is run in the guest, I get some > > > corruption of the IGD frame buffer. If I manually disable PCI memory in > > > the command register, this doesn't happen. I also get some strange > > > artifacts on the PEG display that don't happen when PCI memory is > > > disabled. Should that MSR bit give us the whole a_0000-b_ffff range? > > > > Perhaps. It does that on some old graphics cards I've played with, but > > frankly I have no idea what it does on our hardware. > > > > I'm trying to find out though. If and when I get an answer I'll let you > > know. > > So the answer I basically got is that MSR is the only option here when > the GMCH register can't be used. Supposedly it should work too, but > I felt that I didn't get a 100% definite answer on that subject. I can imagine that the GMCH could be modified if we knew where the bit was that's locking it. I can't find that in the spec though and I assume that's intentional. > I tried it a bit on an IVB machine and PCI and PCIe Matrox G550 cards, > and for me it does seem to work. In the G550 PCIe case there's an extra > PCIe-PCI bridge on the card, and and in the G550 PCI case there's a > PCI-PCI bridge on the card and a PCIe-PCI bridge on the motherboard. > I don't have any native PCIe graphics cards on me to test the no > extra bridges case. > > Based on a bit of manual register/memory banging it looks like the IGD > will decode the access when MSR[1]=1, and won't when MSR[1]=0. Same was > true for PCI_COMMAND[0] in case of VGA I/O. If those bits are disabled > for IGD, the accesses get to the external card. If neither claims it, > I just get 0xff back and writes are ignored. > > Curiously I didn't see any problems when I configured both graphics > devices and bridges to decode/forward VGA resources. The IGD was > always the one to answer and the data didn't seem corrupted. Not sure > why that is. Maybe I just got lucky or something. > > My tests weren't very thorough however, so I may have missed something. Thanks for checking Ville. I wrote a test program myself to blast VGA space through /dev/mem. I agree, it sure seems like the MSR bit is doing it's job. That makes me suspect that I'm not actually getting the bit cleared or that it's being re-enabled somewhere else. I'll do some more digging to make sure the MSR bit is actually cleared on IGD before I start the VM. Thanks! Alex _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
