linux-kernel - Re: [PATCH v5] PCI: Allow PCI bridges to go to D3Hot on all Devicetree based platforms

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Message-ID: <Z32nUpG3KzBOy-PH@google.com>
Date: Tue, 7 Jan 2025 14:14:42 -0800
From: Brian Norris <briannorris@...omium.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>
Cc: Hsin-Yi Wang <hsinyi@...omium.org>, linux-kernel@...r.kernel.org,
	mika.westerberg@...ux.intel.com, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, lukas@...ner.de,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH v5] PCI: Allow PCI bridges to go to D3Hot on all
 Devicetree based platforms

Hi Bjorn,

On Tue, Nov 26, 2024 at 03:17:11PM -0800, Brian Norris wrote:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> 
> Unlike ACPI based platforms, there are no known issues with D3Hot for
> the PCI bridges in Device Tree based platforms. Past discussions (Link
> [1]) determined the restrictions around D3 should be relaxed for all
> Device Tree systems. So let's allow the PCI bridges to go to D3Hot
> during runtime.
> 
> To match devm_pci_alloc_host_bridge() -> devm_of_pci_bridge_init(), we
> look at the host bridge's parent when determining whether this is a
> Device Tree based platform. Not all bridges have their own node, but the
> parent (controller) should.
> 
> Link: https://lore.kernel.org/linux-pci/20240227225442.GA249898@bhelgaas/ [1]
> Link: https://lore.kernel.org/linux-pci/20240828210705.GA37859@bhelgaas/ [2]
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> [Brian: look at host bridge's parent, not bridge node; rewrite
> description]
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> Based on prior work by Manivannan Sadhasivam that was part of a bigger
> series that stalled:
> 
> [PATCH v5 4/4] PCI: Allow PCI bridges to go to D3Hot on all Devicetree based platforms
> https://lore.kernel.org/linux-pci/20240802-pci-bridge-d3-v5-4-2426dd9e8e27@linaro.org/
> 
> I'm resubmitting this single patch, since it's useful and seemingly had
> agreement. I massaged it a bit to relax some restrictions on how the
> Device Tree should look.
> 
> Changes in v5:
> - Pulled out of the larger series, as there were more controversial
>   changes in there, while this one had agreement (Link [2]).
> - Rewritten with a relaxed set of rules, because the above patch
>   required us to modify many device trees to add bridge nodes.

I'm wondering if you have any thoughts on this. Manivannan seemed happy
with this in his reply. I'd like to see this land in mainline, so I can
avoid the hacks that everyone seems to be picking up (such as adding
"pcie_port_pm=force" to their command lines).

(While I'm at it ... apologies for the poor versioning. The subject here
should probably be "v6", since I'm clearly quoting above that the prior
version from Manivannan was v5.)

Thanks,
Brian