Re: [PATCH] PCI: qcom: Handle mixed PERST#/PHY DT configuration

[Kathiravan Thirumoorthy <kathiravan.thirumoorthy@oss.qualcomm.com>]

On 5/31/2026 4:37 PM, Dmitry Baryshkov wrote:
> On Fri, May 08, 2026 at 02:54:19AM -0700, Qiang Yu wrote:
>> The driver currently supports two PERST# and PHY DT configuration. In one
>> case, PHY, PERST#, are described in the RC node. In the other case, they
>> are described in the RP node.
>>
>> A mixed setup is not supported. One common example is PHY on the RP node
>> while PERST# remains on the RC node. In that case the driver goes through
>> the RP parse path, does not find PERST# on RP, and does not report an
>> error because PERST# is optional. Probe can then succeed silently while
>> PERST# is left uncontrolled, and PCIe endpoints fails to work later. This
>> silent probe success makes debugging difficult.
>>
>> Handle this mixed case in the RP parse path by checking whether PERST# is
>> present on RC and, if so, using the RC PERST# GPIO for RP ports while
>> keeping RP parsing for PHY. Emit a warning to indicate mixed DT content so
>> it can be fixed.
>>
>> This keeps mixed systems functional and makes the configuration issue
>> visible instead of failing later at endpoint bring-up.
>>
>> Suggested-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
>> Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
>> ---
>>   drivers/pci/controller/dwc/pcie-qcom.c | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> @@ -1778,6 +1785,14 @@ static int qcom_pcie_parse_ports(struct qcom_pcie *pcie)
>>   	struct device *dev = pcie->pci->dev;
>>   	int ret = -ENODEV;
>>   
>> +	if (of_find_property(dev->of_node, "perst-gpios", NULL)) {
>> +		pcie->reset = devm_gpiod_get_optional(dev, "perst", GPIOD_OUT_HIGH);
>> +		if (IS_ERR(pcie->reset))
>> +			return PTR_ERR(pcie->reset);
>> +
>> +		dev_warn(dev, "Reusing PERST# from Root Complex node. DT needs to be fixed!\n");
> This patch breaks legacy DTs (I stumbled on it on SM8350 HDK), because
> now devm_gpiod_get_optional() in qcom_pcie_parse_legacy_binding()
> returns -EBUSY (as the GPIO is already requested here). I'll send a
> patch fixing the issue, but it's sad to see existing platforms being
> broken for the sake of undeclared "mixed" case.

Dmitry,

I have sent[1] fix for this issue and it is squashed with the offending 
commit itself[2] and part of controller/dwc-qcom in the PCI tree.

[1] 
https://lore.kernel.org/linux-arm-msm/20260526-fix_perst_gpio_handling-v1-1-9170507bb4e9@oss.qualcomm.com/T/#u

[2] 
https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=controller/dwc-qcom&id=1a23bcb452d95f099e530414504c0d99ee076b3f