linux-kernel - Re: [PATCH v3 3/4] PCI: qcom: Parse PERST# from all PCIe bridge nodes

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Message-ID: <blgpkdfx333h6vu25peatl3bbxffe5vuovgmae4osuoahuiryp@owrxkcv63kxb>
Date: Mon, 15 Sep 2025 18:23:45 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: manivannan.sadhasivam@....qualcomm.com, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Saravana Kannan <saravanak@...gle.com>, 
	linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, 
	Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH v3 3/4] PCI: qcom: Parse PERST# from all PCIe bridge nodes

On Fri, Sep 12, 2025 at 06:28:11PM GMT, Bjorn Helgaas wrote:
> On Fri, Sep 12, 2025 at 02:05:03PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > 
> > Devicetree schema allows the PERST# GPIO to be present in all PCIe bridge
> > nodes, not just in Root Port node. But the current logic parses PERST# only
> > from the Root Port nodes. Though it is not causing any issue on the current
> > platforms, the upcoming platforms will have PERST# in PCIe switch
> > downstream ports also. So this requires parsing all the PCIe bridge nodes
> > for the PERST# GPIO.
> > 
> > Hence, rework the parsing logic to extend to all PCIe bridge nodes starting
> > from the Root Port node. If the 'reset-gpios' property is found for a PCI
> > bridge node, the GPIO descriptor will be stored in qcom_pcie_perst::desc
> > and added to the qcom_pcie_port::perst list.
> 
> The switch part doesn't seem qcom specific.  Aren't we going to end up
> with lots of drivers reimplementing something like the
> qcom_pcie_port.perst list?

If this kind of switch is attached to other platforms, then yes. Right now, Qcom
host is the only known DT based host platform that has seen this requirement.

If other drivers also start showing this pattern, I may try to create a common
code somewhere to avoid code duplication. But now, common code is not warranted.

- Mani

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