Re: [PATCH] PCI: qcom: Only check bridge nodes for PERST# GPIOs

[Krishna Chaitanya Chundru]

On 8/29/2026 4:06 PM, Christopher Obbard wrote:
> qcom_pcie_parse_perst() walks the PCIe hierarchy described in the device
> tree below its root port and collects the PERST# GPIOs from each bridge
> node so all PERST# lines can be driven in unison during controller
> bring-up, reset and power sequencing.
>
> However, the recursive device tree walk currently visits every available
> child node without checking that it is a PCI bridge. This allows the walk
> to leave the PCI hierarchy and collect reset lines from children of PCI
> enfpoitn nodes, where those reset lines belong to other drivers.
>
> This is reproducible on the Qualcomm RB3Gen2, where a Renesas uPD720201
> USB host controller sits behind a PCIe switch downstream port. A Genesys
> GL3590 USB hub connected to that controller is described as a child of
> the PCI endpoint:
>
> 	pcie@2,0 {
> 		device_type = "pci";
>
> 		usb-controller@0,0 {
> 			compatible = "pci1912,0014";
>
> 			hub@1 {
> 				compatible = "usb5e3,610";
> 				reset-gpios = <&tlmm 162 GPIO_ACTIVE_HIGH>;
> 			};
> 		};
> 	};
>
> The USB controller is a PCI endpoint, and not a bridge, but the PERST#
> walk descends through it and incorrectly claims the hub's reset GPIO:
>
> 	$ gpioinfo
> 	line 162: unnamed output consumer=PERST#
>
> As a result, the onboard-usb-dev driver cannot acquire its reset GPIO
> during probe:
>
> 	onboard-usb-dev 1c08000.pcie:...:usb-controller@0,0:hub@1: \
> 	  error -EBUSY: failed to get reset GPIO
> 	onboard-usb-dev 1c08000.pcie:...:usb-controller@0,0:hub@1: \
> 	  probe with driver onboard-usb-dev failed with error -16
>
> The GPIO is also added to the root port's PERST# list and is asserted
> and deasserted as part of PCIe reset sequencing. On the RB3Gen2 this
> causes the USB hub to repeatedly re-enumerate:
>
> 	[  116.479598] hub 2-1:1.0: USB hub found
> 	[  116.488601] hub 2-1:1.0: USB hub found
> 	[  116.496971] hub 2-1:1.0: USB hub found
> 	...
>
> This disrupts the hub and devices connected to it.
>
> Restrict the recursive walk to children with device_type "pci", so
> PERST# GPIOs are collected only from PCI bridge nodes and the walk
> does not descend through endpoints.
>
> qocm_pcie_parse_ports() has made the same distinction since
> commit 45df22935bdc ("PCI: qcom: Restrict port parsing only to PCIe
> bridge child nodes"), but the PERST# walk added later did not carry over
> that check.
>
> This bug is distinct from commit 3edb3a038d42 ("PCI: qcom: Skip PERST#
> GPIOs provided by downstream PCIe devices"), which filters PERST# GPIOs
> based on their provider. Here the GPIO is provided by the SoC TLMM; the
> bug is that reset-gpios is consumed from a non-bridge node at all.
>
> Fixes: 2fd60a2edb83 ("PCI: qcom: Parse PERST# from all PCIe bridge nodes")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Christopher Obbard <chris.obbard@xxxxxxxxxxxxxxxx>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx> -
Krishna Chaitanya.
> ---
> USB/Ethernet issue on RB3Gen2.
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index b58a607b713f..89a476c37098 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1953,7 +1953,7 @@ static bool qcom_pcie_is_child_node(struct device *dev,
>  	return false;
>  }
>  
> -/* Parse PERST# from all nodes in depth first manner starting from @np */
> +/* Collect PERST# GPIOs from PCI bridge nodes depth-first, starting at @np */
>  static int qcom_pcie_parse_perst(struct qcom_pcie *pcie,
>  				 struct qcom_pcie_port *port,
>  				 struct device_node *np)
> @@ -2019,6 +2019,9 @@ static int qcom_pcie_parse_perst(struct qcom_pcie *pcie,
>  
>  parse_child_node:
>  	for_each_available_child_of_node_scoped(np, child) {
> +		if (!of_node_is_type(child, "pci"))
> +			continue;
> +
>  		ret = qcom_pcie_parse_perst(pcie, port, child);
>  		if (ret)
>  			return ret;
>
> ---
> base-commit: 570f7e331f5febb30f1384817463c7e42b65ca7d
> change-id: 20260829-wip-obbardc-drivers-pcie-qcom-rb3gen2-usb-fix-ef551ccc0a8d
>
> Best regards,
> --  
> Christopher Obbard <chris.obbard@xxxxxxxxxxxxxxxx>
>
>