On Mon, Feb 24, 2025 at 12:32:36PM +0530, Manivannan Sadhasivam wrote: > On Mon, Feb 24, 2025 at 12:00:46PM +0530, Sai Krishna Musham wrote: > > Add GPIO-based control for the PCIe Root Port PERST# signal. > > > > According to section 2.2 of the PCIe Electromechanical Specification > > (Revision 6.0), PERST# signal has to be deasserted after a delay of > > 100 ms (TPVPERL) to ensure proper reset sequencing during PCIe > > initialization. > > > > Signed-off-by: Sai Krishna Musham <sai.krishna.musham@xxxxxxx> > > --- > > This patch depends on the following patch series. > > https://lore.kernel.org/all/20250217072713.635643-3-thippeswamy.havalige@xxxxxxx/ > > --- > > drivers/pci/controller/pcie-xilinx-cpm.c | 23 +++++++++++++++++++++++ > > 1 file changed, 23 insertions(+) > > > > diff --git a/drivers/pci/controller/pcie-xilinx-cpm.c b/drivers/pci/controller/pcie-xilinx-cpm.c > > index 81e8bfae53d0..0e31b85658e6 100644 > > --- a/drivers/pci/controller/pcie-xilinx-cpm.c > > +++ b/drivers/pci/controller/pcie-xilinx-cpm.c > > @@ -6,6 +6,8 @@ > > */ > > > > #include <linux/bitfield.h> > > +#include <linux/delay.h> > > +#include <linux/gpio/consumer.h> > > #include <linux/interrupt.h> > > #include <linux/irq.h> > > #include <linux/irqchip.h> > > @@ -568,8 +570,29 @@ static int xilinx_cpm_pcie_probe(struct platform_device *pdev) > > struct device *dev = &pdev->dev; > > struct pci_host_bridge *bridge; > > struct resource_entry *bus; > > + struct gpio_desc *reset_gpio; > > int err; > > > > + /* Request the GPIO for PCIe reset signal */ > > + reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW); > > You've defined the polarity as 0x1 in the binding. Which corresponds to > GPIO_ACTIVE_LOW. So if you request the GPIO as GPIOD_OUT_LOW, it means the host > is going to drive the PERST# line as 'high', which corresponds to PERST# > deassert. I don't think you'd want that and if that is what is really happening, > the endpoint state machine would be broken. So I suspect that the polarity of > your PERST# line is wrong. > > - Mani > > > + if (IS_ERR(reset_gpio)) { > > + dev_err(dev, "Failed to request reset GPIO\n"); > > + return PTR_ERR(reset_gpio); > > + } > > + > > + /* Assert the reset signal */ > > + gpiod_set_value(reset_gpio, 0); > > + > > + /* > > + * As per section 2.2 of the PCI Express Card Electromechanical > > + * Specification (Revision 6.0), the deassertion of the PERST# signal > > + * should be delayed by 100 ms (TPVPERL). > > + */ > > + msleep(100); > > + > > + /* Deassert the reset signal */ > > + gpiod_set_value(reset_gpio, 1); > > + Since you are adding PERST# to your DT binding, please make sure that you define it properly (as active low) in the DT binding. Then in the driver things should look like this and nothing else: devm_gpiod_get(..., GPIOD_OUT_HIGH); // will assert PERST# gpiod_set_value(reset_gpio, 1); // assert PERST# (will be a no-op since PERST# is already asserted) msleep(100); gpiod_set_value(reset_gpio, 0); // deassert PERST# Kind regards, Niklas
