So basically, I would like someone to confirm if PEX8747 ACS support works
downstream, even on Intel consumer platforms.
No. Whether or not a PCIe switch supports ACS is irrelevant when it's placed
in a configuration downstream of a PCIe root port that does not support ACS.
The entire path from the endpoint to the IOMMU must support ACS in order for
devices to be isolated.
-----------------------------------------------------------
Sad to hear that, I was really hoping that using the PLX chip could justify its
cost by allowing to workaround the lack of ACS isolation on the mainstream
consumer platform.
Now that you mention that it doesn't matter if downstream switches support ACS
or not, it also means that on Dual GPU cards that uses PLX chips like the
GeForce GTX 690, Tesla M60, Radeon 295X2, Radeon 7990 (Which I use as example
since its the only one that I could get a good lspci dump from after some
googling):
https://bugs.freedesktop.org/attachment.cgi?id=103119
01:00.0 PCI bridge: PLX Technology, Inc. PEX 8747 48-Lane, 5-Port PCI Express
Gen 3 (8.0 GT/s) Switch (rev ba)02:08.0 PCI bridge: PLX Technology, Inc. PEX
8747 48-Lane, 5-Port PCI Express Gen 3 (8.0 GT/s) Switch (rev ba)02:10.0 PCI
bridge: PLX Technology, Inc. PEX 8747 48-Lane, 5-Port PCI Express Gen 3 (8.0
GT/s) Switch (rev ba)03:00.0 VGA compatible controller: Advanced Micro Devices,
Inc. [AMD/ATI] Tahiti XT [Radeon HD 7970/8970 OEM / R9 280X]03:00.1 Audio
device: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti XT HDMI Audio [Radeon HD
7970 Series]04:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI]
Tahiti XT [Radeon HD 7970/8970 OEM / R9 280X]04:00.1 Audio device: Advanced
Micro Devices, Inc. [AMD/ATI] Tahiti XT HDMI Audio [Radeon HD 7970 Series]
...they would ALWAYS be in the same IOMMU Group UNLESS you use them on LGA
2011/2011-3, in which case, the PLX switch ACS support kicks in. Correct?
Also, how does ACS works if coming from the Intel Chipset lanes? I have read
that the consumer Chipsets supports a "ACS-like" feature, according to some
comments in one of your patches for the ACS quirck. My X10SAT has a PLX chip
connected to the Chipset and it seems that I do have proper isolation working
there, so switches with ACS connected to the Chipset seems to work
downstream.In a hypothetical case that I drop such Dual GPU card in a slot
attached to the Chipset, it means that I would get isolation there, but not if
connected to the Processor. Is that correct, too?
BTW, merry christmas.
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