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

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Date:   Fri, 7 Jul 2017 11:01:16 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     wim.ten.have@...cle.com
Cc:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] PCI: Do not enable extended tags on pre-dated (v1.x)
 systems

Hi Wim,

On 7/7/2017 10:53 AM, Sinan Kaya wrote:
> According to extended tags ECN document, all PCIe receivers are expected
> to support extended tags support. It should be safe to enable extended
> tags on endpoints without checking compatibility.
> 
> This assumption seems to be working fine except for the legacy systems.
> The ECN has been written against PCIE spec version 2.0. Therefore, we need
> to exclude all version 1.0 devices from this change as there is HW out
> there that can't handle extended tags.
> 
> Note that the default value of Extended Tags Enable bit is implementation
> specific. Therefore, we are clearing the bit by default when incompatible
> HW is found without assuming that value is zero.
> 
> Reported-by: Wim ten Have <wim.ten.have@...cle.com>
> Link: https://pcisig.com/sites/default/files/specification_documents/ECN_Extended_Tag_Enable_Default_05Sept2008_final.pdf
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1467674
> Fixes: 60db3a4d8cc9 ("PCI: Enable PCIe Extended Tags if supported")
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---

Can you also give this a spin? I don't have a system with v1 PCIe bridges.
I only tested v2 and later code path.

I tried to address Jike Song concerns on this version and removed your tested-by
since the code changed.

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.