linux-kernel - Re: [PATCH V9 1/2] PCI: handle CRS returned by device after FLR

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Message-ID: <20170810215937.GR16580@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 10 Aug 2017 16:59:37 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        alex.williamson@...hat.com, linux-arm-msm@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V9 1/2] PCI: handle CRS returned by device after FLR

On Tue, Aug 08, 2017 at 08:57:24PM -0400, Sinan Kaya wrote:
> Sporadic reset issues have been observed with Intel 750 NVMe drive by
> writing to the reset file in sysfs in a loop. The sequence of events
> observed is as follows:
> 
> - perform a Function Level Reset (FLR)
> - sleep up to 1000ms total
> - read ~0 from PCI_COMMAND
> - warn that the device didn't return from FLR
> - touch the device before it's ready
> 
> An endpoint is allowed to issue Configuration Request Retry Status (CRS)
> following a FLR request to indicate that it is not ready to accept new
> requests. CRS is defined in PCIe r3.1, sec 2.3.1. Request Handling Rules
> and CRS usage in FLR context is mentioned in PCIe r3.1a, sec 6.6.2.
> Function-Level Reset.

Don't we have a similar issue for other types of reset?  I would think
conventional reset, e.g., using secondary bus reset, hotplug slot
power, power management, etc., would have the same situation where a
device might return CRS status.