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

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Date:   Thu, 13 Jul 2017 13:24:33 -0400
From:   Keith Busch <keith.busch@...el.com>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, 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 12:42:44PM -0400, Sinan Kaya wrote:
> On 7/13/2017 12:29 PM, Keith Busch wrote:
> > That wording is just confusing. It looks to me the 1 second polling is
> > to be used following a reset if CRS is not implemented.
> > 
> >   https://pcisig.com/sites/default/files/specification_documents/ECN_RN_29_Aug_2013.pdf
> > 
> > "
> >   Through the mechanisms defined by this ECR, we can avoid the long,
> >   architected, fixed delays following various forms of reset before
> >   software is permitted to perform its first Configuration Request. These
> >   delays are very large:
> > 
> >   1 second if Configuration Retry Status (CRS) is not used
> > "
> > 
> > It goes on to say CRS is usually much lower, but doesn't specify an
> > upper bound either.
> > 
> 
> I see, we got caught on spec language where we don't know what 'its' is. 

Well, I don't know for certain if your original interpretation is
incorrect. Just saying the CRS intention doesn't explicitly stand out to me.

On a side note, I'll also see if I can get clarification on what
expectations the hardware people have for this particular product. Your
observation seems a little high to me, but I don't know if that's
outside the product's limits.