linux-kernel - Re: [PATCH v2 2/2] PCI: pciehp: Clear the optional capabilities in DEVCTL2 on a hot-plug

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Message-ID: <ee23accf-3e2e-773b-dc6c-81d9e18d0d0e@amd.com>
Date:   Wed, 21 Jun 2023 11:55:08 -0700
From:   Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, oohall@...il.com,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Fontenot Nathan <Nathan.Fontenot@....com>
Subject: Re: [PATCH v2 2/2] PCI: pciehp: Clear the optional capabilities in
 DEVCTL2 on a hot-plug

On 6/21/2023 12:12 AM, Lukas Wunner wrote:
> On Fri, Jun 16, 2023 at 04:34:27PM -0700, Smita Koralahalli wrote:
>> On 6/16/2023 11:24 AM, Lukas Wunner wrote:
>>> On Mon, May 22, 2023 at 03:23:31PM -0700, Smita Koralahalli wrote:
>>>> On 5/11/2023 4:19 AM, Lukas Wunner wrote:
>>>>> On Tue, Apr 18, 2023 at 09:05:26PM +0000, Smita Koralahalli wrote:
>>>> Some couple of ways we think could be:
>>>> [1] Check if these bits are enabled by Platform at boot time, clear them
>>>> only it is set during hotplug flow.
>>>> [2] Clear them unconditionally as I did..
>>>> [3] Enable 10-bits tags in Linux when a device is probed just like how
>>>> we do for ARI..
>>>>
>>>> Similarly call pci_enable_atomic_ops_to_root() during a hot add..
>>>
>>> Personally I'm fine with option [2].  If you or Bjorn prefer option [3],
>>> I'm fine with that as well.
>>
>> Looking forward for Bjorn comments!
> 
> You may want to consider first doing [2], i.e. clear the DevCtl2 bits
> on hot removal, and then in a separate step do [3], i.e. add support
> for enabling 10 bit tags and atomic ops in the kernel.  Having that
> would certainly be useful, but it's more complex than just clearing
> the DevCtl2 bits on unplug.  So you may want to do the latter as a
> stop-gap.

Okay I just sent v3 now. I will take care of this in v4 along with other
comments in v3.

Thanks,
Smita
> 
> Thanks,
> 
> Lukas