linux-kernel - Re: [PATCH V2] PCI: Do not enable extended tags on pre-dated (v1.x) systems

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Message-ID: <5f5119fd-64d5-5e7c-fa50-54ac6e6a36b6@codeaurora.org>
Date:   Mon, 10 Jul 2017 20:20:49 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        wim.ten.have@...cle.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 V2] PCI: Do not enable extended tags on pre-dated (v1.x)
 systems

Hi Bjorn,

On 7/10/2017 7:09 PM, Bjorn Helgaas wrote:
> The PCI_EXP_DEVCTL_EXT_TAG bit controls the behavior of the function as a
> Requester.  As far as I can see, it has nothing to do with whether the
> function supports 8-bit tags as a *Completer*, so the implicit assumption
> of the spec is that all Completers always support 8-bit tags.  My guess is
> that's why the ECN thought it would be safe to enable extended tags by
> default.
> 
> If that's the case, this is just a defect in the device (the Completer),
> and we should blacklist it.  Looking at the PCIe Capability version might
> happen to correlate with Completer support for 8-bit tags, but that looks
> like just a coincidence to me.

Sure, I can change to blacklist. I'll not enable it unless the device is blacklisted
via quirks.

Sinan
-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.