Re: [RFC PATCH] PCI: Remove End-End TLP as PASID dependency

[Zhangfei Gao]

On 2020/6/10 äå3:46, Jean-Philippe Brucker wrote:
> On Wed, Jun 10, 2020 at 12:18:14PM +0800, Zhangfei Gao wrote:
> > Some platform devices appear as PCI and have PCI cfg space,
> > but are actually on the AMBA bus.
> > They can support PASID via smmu stall feature, but does not
> > support tlp since they are not real pci devices.
> > So remove tlp as a PASID dependency.
> >
> > Signed-off-by: Zhangfei Gao <zhangfei.gao@xxxxxxxxxx>
> > ---
> >   drivers/pci/ats.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> > index 390e92f..8e31278 100644
> > --- a/drivers/pci/ats.c
> > +++ b/drivers/pci/ats.c
> > @@ -344,9 +344,6 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
> >   	if (WARN_ON(pdev->pasid_enabled))
> >   		return -EBUSY;
> >   
> > -	if (!pdev->eetlp_prefix_path)
> > -		return -EINVAL;
> > -
> This check is useful, and follows the PCI specification (4.0r1.0
> 2.2.10.2 End-End TLP Prefix Processing: "Software should ensure that TLPs
> containing End-End TLP Prefixes are not sent to components that do not
> support them.")
Thanks Jean,
> Why not set the eetlp_prefix_path bit from a PCI quirk?  Unlike the stall
> problem from the other thread, this one looks like a simple design mistake
> that can be fixed easily in future iterations of the platform: just set
> the "End-End TLP Prefix Supported" bit in the Device Capability 2 Register
> of all bridges.
Yes, we can still set eetlp_prefix_path bit from a PCI quirk.

And we also have considered adding this bit in Device Capability 2 
Register in future silicon.
But we hesitated that it does reflect the real function: from register, 
it can support tlp, but in fact, it does not.

Thanks