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

Bjorn Helgaas
2024-08-27T23:49:04Z

From: Bjorn Helgaas <bhelgaas@google.com>

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(-)

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2.34.1