Re: [PATCH v3] PCI: Add D3 support for PCI bridges in DT based platforms

From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: "Bjorn Helgaas" <bhelgaas@google.com>,
	"Bjorn Andersson" <andersson@kernel.org>,
	"Konrad Dybcio" <konrad.dybcio@linaro.org>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Rob Herring" <robh@kernel.org>, "Lukas Wunner" <lukas@wunner.de>,
	"Mika Westerberg" <mika.westerberg@linux.intel.com>,
	quic_krichai@quicinc.com, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v3] PCI: Add D3 support for PCI bridges in DT based platforms
Date: Tue, 27 Feb 2024 22:38:40 +0530	[thread overview]
Message-ID: <20240227170840.GR2587@thinkpad> (raw)
In-Reply-To: <20240227162535.GA239073@bhelgaas>

On Tue, Feb 27, 2024 at 10:25:35AM -0600, Bjorn Helgaas wrote:

[...]

> > Ok, I got the issue. TBH, I added the device tree property based on
> > the existing quirks for the ACPI devices. But none of the DT based
> > platforms I'm aware of (even the legacy Qcom MSM8996 chipset
> > released in early 2016) doesn't have any issue with D3hot. But I'm
> > just nervous to assume it is the case for all the DT based platforms
> > in the wild.
> > 
> > But to proceed further, what is your preference? Should we ammend
> > the DT property to make it explicit that the propery only focuses on
> > the D3hot capability of the bridge and it works as per the spec
> > (PMCSR) or bite the bullet and enable D3hot for all the non-ACPI
> > platforms?
> > 
> > We can add quirks for the bridges later on if we happen to receive
> > any bug report.
> 
> I would assume all devices support D3hot via PMCSR per spec.  We can
> add quirks if we discover something that doesn't.
> 

When you say "all devices", are you referring to bridges in DT platforms or the
bridges across all platforms?

- Mani

> If we add annotations that "this device works correctly", we're
> digging a hole for ourselves because it's impossible to remove those
> annotations and they complicate all future maintenance.
> 
> Bjorn

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