On Tue, Dec 05, 2017 at 09:35:22PM +0100, Rudolf Marek wrote: > Dne 5.12.2017 v 20:07 Bjorn Helgaas napsal(a): > > So if I understand correctly, you have > > > > - A bridge with PCI_BRIDGE_CTL_VGA set but VGA_16BIT_EN is clear > > Yes > > > - A peer of the bridge with an I/O BAR set to some alias of > > 0x3c0-0x3df > > It is not a peer bridge, but some other bridge on bus 0. The non-working device is > a Audigy PCI card (05:00.0) 00:01.0 and 00:1c.3 are peers in the sense that they're both on the same bus. 00:1c.3 doesn't have a *BAR* that contains 0x3c0, but I think it does have an I/O *window* set to an alias of 0x3c0, like this (we don't actually print the implicit VGA bridge windows, but maybe we should): 00:01.0 PCI bridge to [bus 01] 00:01.0 implicit bridge window [io 0x03c0-0x03df] + ISA aliases 01:xx.0 VGA device legacy resource [io 0x03c0-0x03df] 00:1c.3 PCI bridge to [bus 04-05] 00:1c.3 bridge window [io 0xc000-0xcfff] 04:00.0 PCI bridge to [bus 05] 04:00.0 bridge window [io 0xc000-0xcfff] 05:00.0 Audigy reg 0x10: [io 0xcfc0-0xcfdf] 0xcfc0 is a 10-bit alias of 0x03c0, so both bridges (00:01.0 and 00:1c.3) will claim it. > The path is 00:1c.3 (Intel PCIe bridge) -> 4:00.0 (ITE PCIe-PCI bridge) -> 5:00.0 (audigy) > The other bridge is 00:01.0 which connects to some VGA on bus 1. > > The Audigy has only one resource: > > Region 0: I/O ports at cfc0 [size=32] > > Which collides with the 0x3b0. We used "isadump -f" to verify we indeed see an alias. > Rayer booted to DOS, edited the BAR and loadlin back to Linux and the device works, > so it was that. Later he reported that setting the bit4 also fixed that. > > > > In this case I think both the bridge and the peer device will claim > > accesses to 0x3c0-0x3df, which is a bad thing. > > Yes, the isadump -f confirmed that. > > And your proposal is that Linux should either > > > > - Turn on VGA_16BIT_EN (if supported by the bridge), or > > > > - If VGA_16BIT_EN is not supported by the bridge, try to reassign > > the peer I/O BAR so it doesn't conflict with the 0x3c0-0x3df > > aliases > > The Aliases are: > > 0x3B0 - 0x3BB and 0x3C0 - 0x3DF and it seems that also VGA palette snoops > and VGA palette snoops: 0x3C6, 0x3C8, 0x3C9 > > It seems that the VGA_16BIT_EN could also control the palette snoops alias, > so in the end it should remove all aliases. > I hope someone access to more recent PCI bridge specs can confirm. The PCI-to-PCI Bridge spec, r1.2, sec 3.2.5.18, says VGA_16BIT_EN controls the bridge decoding for "all VGA I/O register accesses that are forwarded from primary to secondary." I would say that would include VGA palette snoops. > > If I'm understanding correctly, this sounds very reasonable. > > Yes exactly. Question is why the insanity alias exists in the first place. > What Mr. PCI tried to fix or break with that alias design? > Besides making logic simpler, I have no idea. I think this 10-bit aliasing is a compatibility feature for ISA. > >> I suspect it will fix couple of problems people were seeing with old > >> PCI cards as they tend to have the I/O regions (I stumbled upon > >> various reports when was suspecting the PCIe to PCI ITE chip and > >> interrupt routing problems) > > > > To help understand and document this better, it would be nice to see a > > complete dmesg log and "lspci -vv" output (as root) showing the > > problem. A kernel.org bugzilla would be a good place to store this. > > Yes sure, in what category > > drivers/pci or platform/hardware? drivers/pci > > It would also be great to collect up the other reports you've found > > and see if we can definitively tie them to this issue and potentially > > test a fix. > > Oh, hm, those were random searches using a search engine. I was talking about [1], > but reading it again, all issues were interrupt related. > > I'll try to reproduce my searches. > > Btw, latest pciutils-3.5.6 also lack of decoding of the bit4. I added to Martin Mares to CC. > > I can prepare a patch for PCIutils if needed. Martin, please tell. Yes, a pciutils patch would be great. It would be ideal if you could prepare the patch and send it to Martin and cc linux-pci. > [1] https://bugzilla.kernel.org/show_bug.cgi?id=43238
