netdev - Re: [PATCH 14/17] r8169: Use pcie_lnkctl_clear_and

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Message-ID: <7bb6e2c9-835c-c8d9-f8a5-baa3d3b03b12@gmail.com>
Date: Thu, 11 May 2023 22:17:18 +0200
From: Heiner Kallweit <hkallweit1@...il.com>
To: Lukas Wunner <lukas@...ner.de>
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 linux-pci@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>,
 Rob Herring <robh@...nel.org>, Lorenzo Pieralisi
 <lorenzo.pieralisi@....com>, Krzysztof Wilczy??ski <kw@...ux.com>,
 nic_swsd@...ltek.com, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/17] r8169: Use pcie_lnkctl_clear_and_set() for changing
 LNKCTL

On 11.05.2023 22:02, Lukas Wunner wrote:
> On Thu, May 11, 2023 at 09:49:52PM +0200, Heiner Kallweit wrote:
>> On 11.05.2023 15:14, Ilpo Järvinen wrote:
>>> Don't assume that only the driver would be accessing LNKCTL. ASPM
>>> policy changes can trigger write to LNKCTL outside of driver's control.
>>>
>>> Use pcie_lnkctl_clear_and_set() which does proper locking to avoid
>>> losing concurrent updates to the register value.
>>
>> Wouldn't it be more appropriate to add proper locking to the
>> underlying pcie_capability_clear_and_set_word()?
> 
> PCI config space accessors such as this one are also used in hot paths
> (e.g. interrupt handlers).  They should be kept lean (and lockless)

I *think* in case the system uses threaded interrupts you may need locking
also in interrupt handlers.

> by default.  We only need locking for specific PCIe Extended Capabilities
> which are concurrently accessed by PCI core code and drivers.
> 
> Thanks,
> 
> Lukas