linux-kernel - Re: [PATCH V4] PCI: handle CRS returned by device after FLR

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Date:   Thu, 13 Jul 2017 18:38:59 -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, vikrams@...eaurora.org,
        Lorenzo.Pieralisi@....com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V4] PCI: handle CRS returned by device after FLR

On Thu, Jul 13, 2017 at 11:44:12AM -0400, Sinan Kaya wrote:
> On 7/13/2017 8:17 AM, Bjorn Helgaas wrote:
> >> he spec is calling to wait up to 1 seconds if the device is sending CRS.
> >> The NVMe device seems to be requiring more. Relax this up to 60 seconds.
> > Can you add a pointer to the "1 second" requirement in the spec here?
> > We use 60 seconds in pci_scan_device() and acpiphp_add_context().  Is
> > there a basis in the spec for the 60 second timeout?
> 
> This does not specify a hard limit above on how long SW need to wait. 

I wouldn't expect a *maximum* time we can wait.  I'm looking for the
minimum times the spec requires.

If you're claiming "the spec is calling to wait up to 1 second", I
just want to know where in the spec it says that.  That helps in the
future when we need to maintain code like this.

> If I remember it right from CRS commit messages, 60 seconds was coming from
> some PCIe switch taking too long to boot.

If you have a pointer to this, please include it.  The earliest thing
I can find is when Linux was imported into git (1da177e4c3f4
("Linux-2.6.12-rc2")), which includes a 60 second timeout:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/probe.c?id=1da177e4c3f4#n686