linux-kernel - Re: [PATCH v3 1/1] PCI: Add translated request only flag for pci_enable

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Date:   Tue, 31 Jan 2023 20:25:05 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     baolu.lu@...ux.intel.com, Bjorn Helgaas <bhelgaas@...gle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Matt Fagnani <matt.fagnani@...l.net>,
        Christian König <christian.koenig@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Vasant Hegde <vasant.hegde@....com>,
        Tony Zhu <tony.zhu@...el.com>, linux-pci@...r.kernel.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] PCI: Add translated request only flag for
 pci_enable_pasid()

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.

Best regards,
baolu