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Message-ID: <4599d885-219f-3ee0-f425-62746f31cc67@amd.com>
Date: Tue, 27 Jun 2023 10:38:54 -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>,
Jay Cornwall <Jay.Cornwall@....com>,
Felix Kuehling <Felix.Kuehling@....com>
Subject: Re: [PATCH v3 2/2] PCI: pciehp: Clear the optional capabilities in
DEVCTL2 on a hot-plug
On 6/22/2023 2:42 PM, Lukas Wunner wrote:
> [cc += Jay, Felix]
>
> On Thu, Jun 22, 2023 at 02:02:12PM -0700, Smita Koralahalli wrote:
>> Would it be fair to just reuse pci_enable_atomic_ops_to_root() for
>> Atomic_Ops configuration?
>
> Hm, that's a good question. I'm not an expert on that corner of
> the PCI core.
>
> But indeed what you could try is amend that function to not only
> *set* PCI_EXP_DEVCTL2_ATOMIC_REQ if it's supported, but to also
> *clear* it if it's not supported.
>
> And you'd have to call pci_enable_atomic_ops_to_root() on enumeration,
> e.g. from pci_init_capabilities().
>
> That should obviate the need to call pci_enable_atomic_ops_to_root()
> from drivers, so you could probably remove the call from all the
> drivers which currently call it (amdgpu, infiniband, mellanox),
> in one separate patch per driver.
>
> An then you could drop the EXPORT clause for pci_enable_atomic_ops_to_root()
> and make it private to the PCI core.
>
> So that would be 5 patches (enablement/disablement on enumeration,
> amendmend of the 3 drivers, making the call private).
>
> I'm not sure if anyone will cry foul if you do that but if you want
> to give it a try, go for it. :)
Okay, I see there are no objections except for Bjorn/Jay's comments on
"But there could be devices where AtomicOps are nominally supported but
untested or broken.."
Would this be an issue?
If not, I will start working on those 5 patches.
Thanks,
Smita
>
> I don't now why commit 430a23689dea, which introduced
> pci_enable_atomic_ops_to_root(), chose to add it as a library function
> which is only called from specific drivers, instead of universally
> enabling the feature for all devices. Adding the commit authors to cc
> so they can chime in.
>
> Thanks,
>
> Lukas
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