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

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Message-Id: <20240827234848.4429-1-helgaas@kernel.org>
Date: Tue, 27 Aug 2024 18:48:45 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: linux-pci@...r.kernel.org
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"Maciej W . Rozycki" <macro@...am.me.uk>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Lukas Wunner <lukas@...ner.de>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Duc Dang <ducdang@...gle.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [RFC PATCH 0/3] PCI: Use Configuration RRS to wait for device ready

From: Bjorn Helgaas <bhelgaas@...gle.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(-)

-- 
2.34.1