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Date:   Fri, 23 Jun 2023 08:12:53 -0500
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Subject: Re: [PATCH v3 2/2] PCI: pciehp: Clear the optional capabilities in
 DEVCTL2 on a hot-plug
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To:     Lukas Wunner <lukas@wunner.de>,
        Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bjorn Helgaas <bhelgaas@google.com>, oohall@gmail.com,
        Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Yazen Ghannam <yazen.ghannam@amd.com>,
        Fontenot Nathan <Nathan.Fontenot@amd.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>
References: <20230621185152.105320-1-Smita.KoralahalliChannabasappa@amd.com>
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From:   Jay Cornwall <jay.cornwall@amd.com>
In-Reply-To: <20230622214247.GB11993@wunner.de>
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On 6/22/2023 16:42, Lukas Wunner wrote:

> 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.

IIRC during the initial design discussion on linux-pci this approach was suggested to avoid triggering potential bugs in devices without AtomicOps support. See quote below.

I've no objections to changing it.

On 2016-05-06 10:48, Bjorn Helgaas wrote:

> Once enabled in Device Control 2, a device's use of AtomicOps is
> competely device-specific.  In many cases, the device probably doesn't
> support AtomicOps, so enabling them would be a no-op.  But there could
> be devices where AtomicOps are nominally supported but untested or
> broken.  Even if we didn't change their drivers, those devices could
> start using AtomicOps, so I'm not comfortable with the PCI core
> enabling AtomicOp requests indiscriminately.