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Message-ID: <20250708232327.GA2169793@bhelgaas>
Date: Tue, 8 Jul 2025 18:23:27 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Sai Krishna Musham <sai.krishna.musham@....com>
Cc: bhelgaas@...gle.com, lpieralisi@...nel.org, kw@...ux.com,
mani@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, cassel@...nel.org, lkp@...el.com,
linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, michal.simek@....com,
bharat.kumar.gogada@....com, thippeswamy.havalige@....com
Subject: Re: [PATCH v4 2/2] PCI: amd-mdb: Add support for PCIe RP PERST#
signal handling
On Thu, Jun 26, 2025 at 11:19:06AM +0530, Sai Krishna Musham wrote:
> Add support for handling the AMD Versal Gen 2 MDB PCIe Root Port PERST#
> signal via a GPIO by parsing the new PCIe bridge node to acquire the
> reset GPIO.
>
> As part of this, update the interrupt controller node parsing to use
> of_get_child_by_name() instead of of_get_next_child(), since the PCIe
> node now has multiple children. This ensures the correct node is
> selected during initialization.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202506241020.rPD1a2Vr-lkp@intel.com/
Omit these tags. This kernel test robot report is basically a code
review comment that doesn't need to be acknowledged here (the robot's
report says:
If you fix the issue in a separate patch/commit (i.e. not just a new
version of the same patch/commit), kindly add following tags ...
IIUC this is just a new version of the same patch, so doesn't need the
tags.
> Signed-off-by: Sai Krishna Musham <sai.krishna.musham@....com>
> ---
> Changes in v4:
> - Resolve kernel test robot warning.
> https://lore.kernel.org/oe-kbuild-all/202506241020.rPD1a2Vr-lkp@intel.com/
> - Update commit message.
>
> Changes in v3:
> - Implement amd_mdb_parse_pcie_port to parse bridge node for reset-gpios property.
>
> Changes in v2:
> - Change delay to PCIE_T_PVPERL_MS
>
> v3 https://lore.kernel.org/r/20250618080931.2472366-1-sai.krishna.musham@amd.com/
> v2 https://lore.kernel.org/r/20250429090046.1512000-1-sai.krishna.musham@amd.com/
> v1 https://lore.kernel.org/r/20250326041507.98232-1-sai.krishna.musham@amd.com/
> ---
> drivers/pci/controller/dwc/pcie-amd-mdb.c | 46 ++++++++++++++++++++++-
> 1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-amd-mdb.c b/drivers/pci/controller/dwc/pcie-amd-mdb.c
> index 9f7251a16d32..f011a83550b9 100644
> --- a/drivers/pci/controller/dwc/pcie-amd-mdb.c
> +++ b/drivers/pci/controller/dwc/pcie-amd-mdb.c
> @@ -18,6 +18,7 @@
> #include <linux/resource.h>
> #include <linux/types.h>
>
> +#include "../../pci.h"
> #include "pcie-designware.h"
>
> #define AMD_MDB_TLP_IR_STATUS_MISC 0x4C0
> @@ -56,6 +57,7 @@
> * @slcr: MDB System Level Control and Status Register (SLCR) base
> * @intx_domain: INTx IRQ domain pointer
> * @mdb_domain: MDB IRQ domain pointer
> + * @perst_gpio: GPIO descriptor for PERST# signal handling
> * @intx_irq: INTx IRQ interrupt number
> */
> struct amd_mdb_pcie {
> @@ -63,6 +65,7 @@ struct amd_mdb_pcie {
> void __iomem *slcr;
> struct irq_domain *intx_domain;
> struct irq_domain *mdb_domain;
> + struct gpio_desc *perst_gpio;
> int intx_irq;
> };
>
> @@ -284,7 +287,7 @@ static int amd_mdb_pcie_init_irq_domains(struct amd_mdb_pcie *pcie,
> struct device_node *pcie_intc_node;
> int err;
>
> - pcie_intc_node = of_get_next_child(node, NULL);
> + pcie_intc_node = of_get_child_by_name(node, "interrupt-controller");
> if (!pcie_intc_node) {
> dev_err(dev, "No PCIe Intc node found\n");
> return -ENODEV;
> @@ -402,6 +405,34 @@ static int amd_mdb_setup_irq(struct amd_mdb_pcie *pcie,
> return 0;
> }
>
> +static int amd_mdb_parse_pcie_port(struct amd_mdb_pcie *pcie)
> +{
> + struct device *dev = pcie->pci.dev;
> + struct device_node *pcie_port_node;
> +
> + pcie_port_node = of_get_next_child_with_prefix(dev->of_node, NULL, "pcie");
> + if (!pcie_port_node) {
> + dev_err(dev, "No PCIe Bridge node found\n");
> + return -ENODEV;
> + }
> +
> + /* Request the GPIO for PCIe reset signal and assert */
> + pcie->perst_gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(pcie_port_node),
> + "reset", GPIOD_OUT_HIGH, NULL);
> + if (IS_ERR(pcie->perst_gpio)) {
> + if (PTR_ERR(pcie->perst_gpio) != -ENOENT) {
> + of_node_put(pcie_port_node);
> + return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
> + "Failed to request reset GPIO\n");
> + }
> + pcie->perst_gpio = NULL;
> + }
> +
> + of_node_put(pcie_port_node);
> +
> + return 0;
> +}
> +
> static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
> struct platform_device *pdev)
> {
> @@ -426,6 +457,14 @@ static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
>
> pp->ops = &amd_mdb_pcie_host_ops;
>
> + if (pcie->perst_gpio) {
> + mdelay(PCIE_T_PVPERL_MS);
> +
> + /* Deassert the reset signal */
> + gpiod_set_value_cansleep(pcie->perst_gpio, 0);
> + mdelay(PCIE_T_RRS_READY_MS);
> + }
> +
> err = dw_pcie_host_init(pp);
> if (err) {
> dev_err(dev, "Failed to initialize host, err=%d\n", err);
> @@ -444,6 +483,7 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
> struct device *dev = &pdev->dev;
> struct amd_mdb_pcie *pcie;
> struct dw_pcie *pci;
> + int ret;
>
> pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
> if (!pcie)
> @@ -454,6 +494,10 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
>
> platform_set_drvdata(pdev, pcie);
>
> + ret = amd_mdb_parse_pcie_port(pcie);
> + if (ret)
> + return ret;
I'm not a DT expert, but doesn't this break if you run
amd_mdb_parse_pcie_port() on a system with an existing DT that lacks
the pcie@0,0 stanza you added to the binding in patch [1/2]?
I.e., amd_mdb_parse_pcie_port() will return -ENODEV in that case, and
the probe will now fail?
It's good to add new functionality, but if the driver runs with a DT
that doesn't describe the new functionality, it should fall back to
the previous behavior (without the new functionality) instead of
failing completely.
> return amd_mdb_add_pcie_port(pcie, pdev);
> }
>
> --
> 2.44.1
>
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