On Tue, Jan 31, 2023 at 08:25:05PM +0800, Baolu Lu wrote: > On 2023/1/31 2:38, Bjorn Helgaas wrote: > > PCIe r6.0, sec 6.20.1: > > > > A Function is not permitted to generate Requests using Translated > > Addresses and a PASID unless both PASID Enable and Translated > > Requests with PASID Enable are Set. > > > > You want AMD graphics devices to do DMA with translated addresses and > > PASID, right? pci_enable_pasid() sets PASID Enable > > (PCI_PASID_CTRL_ENABLE), but I don't see where "Translated Requests > > with PASID Enable" is set. We don't even have a #define for it. > > > > I would think we should check "Translated Requests with PASID > > Supported" before setting "Translated Requests with PASID Enable", > > too? > > This seems to be an ECN for PCIe 5.x: > > https://members.pcisig.com/wg/PCI-SIG/document/14929 > > What I read from this ECN is that, > > With this ECN, translated memory requests for PASIDs are not allowed to > carry a PASID prefix if "Translated Requests with PASID Enabled" is not > set. It does not mean whether the device can generate translated memory > requests for PASID, but whether the memory request can carry a PASID > prefix. My assumption that "you want AMD graphics devices to do DMA with translated addresses and PASID" was wrong. Per Jason [1], it sounds like the AMD GPU generates Translation Requests (sec 10.2.2) with a PASID. The GPU will cache the translated address from the Translation Completion in its local ATC, and will do DMA (MemRd/Wr) with that translated address but *without* PASID prefixes. That makes sense because (PASID, IOVA) maps to a translated address, e.g., a a CPU physical address, and the GPU can DMA to that address directly without needing the PASID. Bjorn [1] https://lore.kernel.org/r/Y9nQK9P3HOxEeZ4U@xxxxxxxxxx
