On 8/21/2017 4:23 PM, Bjorn Helgaas wrote:

On Mon, Aug 21, 2017 at 03:37:06PM -0400, Sinan Kaya wrote:

quoted

On 8/21/2017 3:18 PM, Bjorn Helgaas wrote:
...
if (pci_bus_crs_pending(id))
	return pci_bus_wait_crs(dev->bus, dev->devfn, &id, 60000);

quoted

I think that makes sense.  We'd want to check for CRS SV being
enabled, e.g., maybe read PCI_EXP_RTCTL_CRSSVE back in
pci_enable_crs() and cache it somewhere.  Maybe a crs_sv_enabled bit
in the root port's pci_dev, and check it with something like what
pcie_root_rcb_set() does?

You can observe CRS under the following conditions

1. root port <-> endpoint 
2. bridge <-> endpoint 
3. root port<->bridge

I was relying on the fact that we are reading 0x001 as an indication that
this device detected CRS. Maybe, this is too indirect.

If we also want to capture the capability, I think the right thing is to
check the parent capability.

bool pci_bus_crs_vis_supported(struct pci_dev *bridge)
{
	if (device type(bridge) == root port)
		return read(root_crs_register_reg);

	if (device type(bridge) == switch)
		return read(switch_crs_register);

I don't understand this part.  AFAIK, CRS SV is only a feature of root
ports.  The capability and enable bits are in the Root Capabilities
and Root Control registers.

No question about it.

It's certainly true that a device below a switch can respond with a
CRS completion, but the switch is not the requester, and my
understanding is that it would not take any action on the completion
other than passing it upstream.

I saw some bridge references in the spec for CRS. I was going to do
some research for it. You answered my question. I was curious how this
would impact the behavior.

"Bridge Configuration Retry Enable ? When Set, this bit enables PCI Express
to PCI/PCI-X bridges to return Configuration Request Retry Status (CRS) in
response to Configuration Requests that target devices below the bridge. 
Refer to the PCI Express to PCI/PCI-X Bridge Specification, Revision 1.0 for
further details."

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.