Re: [RFC PATCH 0/3] PCI: Use Configuration RRS to wait for device ready

[Mario Limonciello]

On 8/27/2024 18:48, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>
> After a device reset, pci_dev_wait() waits for a device to become
> completely ready by polling the PCI_COMMAND register.  The spec envisions
> that software would instead poll for the device to stop responding to
> config reads with Completions with Request Retry Status (RRS).
>
> Polling PCI_COMMAND leads to hardware retries that are invisible to
> software and the backoff between software retries doesn't work correctly.
>
> Root Ports are not required to support the Configuration RRS Software
> Visibility feature that prevents hardware retries and makes the RRS
> Completions visible to software, so this series only uses it when available
> and falls back to PCI_COMMAND polling when it's not.
>
> This is completely untested and posted for comments.
>
> Bjorn Helgaas (3):
>    PCI: Wait for device readiness with Configuration RRS
>    PCI: aardvark: Correct Configuration RRS checking
>    PCI: Rename CRS Completion Status to RRS
>
>   drivers/bcma/driver_pci_host.c             | 10 ++--
>   drivers/pci/controller/dwc/pcie-tegra194.c | 18 +++---
>   drivers/pci/controller/pci-aardvark.c      | 64 +++++++++++-----------
>   drivers/pci/controller/pci-xgene.c         |  6 +-
>   drivers/pci/controller/pcie-iproc.c        | 18 +++---
>   drivers/pci/pci-bridge-emul.c              |  4 +-
>   drivers/pci/pci.c                          | 41 +++++++++-----
>   drivers/pci/pci.h                          | 11 +++-
>   drivers/pci/probe.c                        | 33 +++++------
>   include/linux/bcma/bcma_driver_pci.h       |  2 +-
>   include/linux/pci.h                        |  1 +
>   include/uapi/linux/pci_regs.h              |  6 +-
>   12 files changed, 117 insertions(+), 97 deletions(-)

Although this looks like a useful series, I'm sorry to say but this 
doesn't solve the issue that Gary and I raised.  We double checked today 
and found that reading the vendor ID works just fine at this time.

I think that we're still better off polling PCI_PM_CTRL to "wait" for D0 
after the state change from D3cold.