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

[Dmitry Baryshkov]

On Tue, Jun 02, 2026 at 10:04:22AM +0530, Kathiravan Thirumoorthy wrote:
> 
> 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@xxxxxxxxxxxxxxxx>
> > > Signed-off-by: Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> > > ---
> > >   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.

Ack, thanks

> 
> [1] https://lore.kernel.org/linux-arm-msm/20260526-fix_perst_gpio_handling-v1-1-9170507bb4e9@xxxxxxxxxxxxxxxx/T/#u
> 
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=controller/dwc-qcom&id=1a23bcb452d95f099e530414504c0d99ee076b3f
> 

-- 
With best wishes
Dmitry