linux-kernel - Re: [PATCH 00/14] PCI: qcom: Simulate PCIe hotplug using 'global' interrupt

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Message-ID: <20240716035959.GA3446@thinkpad>
Date: Tue, 16 Jul 2024 09:29:59 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 00/14] PCI: qcom: Simulate PCIe hotplug using 'global'
 interrupt

On Mon, Jul 15, 2024 at 10:10:47PM +0200, Konrad Dybcio wrote:
> On 15.07.2024 7:33 PM, Manivannan Sadhasivam via B4 Relay wrote:
> > Hi,
> > 
> > This series adds support to simulate PCIe hotplug using the Qcom specific
> > 'global' IRQ. Historically, Qcom PCIe RC controllers lack standard hotplug
> > support. So when an endpoint is attached to the SoC, users have to rescan the
> > bus manually to enumerate the device. But this can be avoided by simulating the
> > PCIe hotplug using Qcom specific way.
> > 
> > Qcom PCIe RC controllers are capable of generating the 'global' SPI interrupt
> > to the host CPUs. The device driver can use this event to identify events such
> > as PCIe link specific events, safety events etc...
> > 
> > One such event is the PCIe Link up event generated when an endpoint is detected
> > on the bus and the Link is 'up'. This event can be used to simulate the PCIe
> > hotplug in the Qcom SoCs.
> > 
> > So add support for capturing the PCIe Link up event using the 'global' interrupt
> > in the driver. Once the Link up event is received, the bus underneath the host
> > bridge is scanned to enumerate PCIe endpoint devices, thus simulating hotplug.
> > 
> > This series also has some cleanups to the Qcom PCIe EP controller driver for
> > interrupt handling.
> 
> Welp I've reviewed this series, and only now came to the realization that
> the PCIe RC and PCIe EP descriptions are borderline identical.. perhaps for
> new platforms we could get a new binding that could have a structure like
> 
> pcie@...d1234 {
> 	// commmon properties
> 
> 	pcie-ep {
> 		// ep specifics
> 	};
> 
> 	pcie-rc {
> 		// rc specifics
> 	}
> };
> 
> or better yet, have a single node no matter what, but consume only the
> required resources from the driver and have something akin to phy-mode,
> just like we solved the DP/eDP dual-mode controller story
> 
> Although here it may not be so simple given there's properties like
> iommu-map that map to bus specifics..
> 

It's not that simple, but I wouldn't rule out the technical possibility. Also
with the addition of PCIe bridges and endpoint descriptions (thanks to the new
pwrctl driver), it will look even messier.

And then there will also be the driver side ugliness...

- Mani

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