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

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Message-ID: <20240910225516.GA608142@bhelgaas>
Date: Tue, 10 Sep 2024 17:55:16 -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: Re: [RFC PATCH 0/3] PCI: Use Configuration RRS to wait for device
 ready

On Tue, Aug 27, 2024 at 06:48:45PM -0500, Bjorn Helgaas wrote:
> 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(-)

I provisionally applied this on pci/crs for v6.12.  Please let me know
of any concerns.  I do have one internal test report, but more would
be better since I know this affects many devices.

Bjorn