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Message-ID: <20250812194113.GA199940@bhelgaas>
Date: Tue, 12 Aug 2025 14:41:13 -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, 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 v7 2/2] PCI: amd-mdb: Add support for PCIe RP PERST#
signal handling
On Thu, Aug 07, 2025 at 01:10:19PM +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. If the bridge node is not found, fall back to acquiring it
> from the PCIe host bridge node.
>
> 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
> host bridge node now has multiple children. This ensures the correct
> node is selected during initialization.
>
> Signed-off-by: Sai Krishna Musham <sai.krishna.musham@....com>
> ---
> Changes in v7:
> - Use for_each_child_of_node_with_prefix() to iterate through PCIe
> Bridge nodes.
>
> Changes in v6:
> - Simplified error checking condition logic.
> - Removed unnecessary fallback message.
>
> Changes in v5:
> - Add fall back mechanism to acquire reset GPIO from PCIe node when PCIe Bridge
> node is not present.
>
> 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
>
> v6 https://lore.kernel.org/all/20250719030951.3616385-1-sai.krishna.musham@amd.com/
> v5 https://lore.kernel.org/all/20250711052357.3859719-1-sai.krishna.musham@amd.com/
> v4 https://lore.kernel.org/all/20250626054906.3277029-1-sai.krishna.musham@amd.com/
> 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 | 52 ++++++++++++++++++++++-
> 1 file changed, 51 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..3c6e837465bb 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 +405,28 @@ 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 __maybe_unused;
> +
> + /*
> + * This platform currently supports only one Root Port, so the loop
> + * will execute only once.
> + * TODO: Enhance the driver to handle multiple Root Ports in the future.
> + */
> + for_each_child_of_node_with_prefix(dev->of_node, pcie_port_node, "pcie") {
This is only the second user of for_each_child_of_node_with_prefix()
in the whole tree. Also the only use of "__maybe_unused" in
drivers/pci/controller/.
Most of the PCI controller drivers use
for_each_available_child_of_node_scoped(); can we do the same here?
The apple, kirin, mt7621, mtk, and qcom drivers are examples. I think
the qcom structure is pretty good, and it has a similar fallback path
for DTs without Root Port nodes (qcom_pcie_parse_legacy_binding()):
qcom_pcie_probe
ret = qcom_pcie_parse_ports
for_each_available_child_of_node_scoped(dev->of_node, of_port)
qcom_pcie_parse_port(of_port)
reset = devm_fwnode_gpiod_get(..., "reset", ...)
if (ret)
qcom_pcie_parse_legacy_binding
IIUC the current amd-mdb hardware only supports a single Root Port, so
I don't think you need a TODO, since there's no point in that
enhancement until hardware supports multiple RPs.
But I probably *would* add a check here so that if we run the current
driver on future hardware that does have multiple Root Ports with
separate resets for each RP, there's at least a chance that the first
RP will work. E.g.,
amd_mdb_parse_pcie_port(...)
{
if (pcie->perst_gpio) {
dev_warn("Ignoring extra Root Port\n");
return 0;
}
pcie->perst_gpio = devm_fwnode_gpiod_get(...);
> + 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))
> + return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
> + "Failed to request reset GPIO\n");
> + return 0;
> + }
> +
> + return -ENODEV;
> +}
> +
> static int amd_mdb_add_pcie_port(struct amd_mdb_pcie *pcie,
> struct platform_device *pdev)
> {
> @@ -426,6 +451,12 @@ 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);
> + gpiod_set_value_cansleep(pcie->perst_gpio, 0);
> + mdelay(PCIE_RESET_CONFIG_WAIT_MS);
> + }
> +
> err = dw_pcie_host_init(pp);
> if (err) {
> dev_err(dev, "Failed to initialize host, err=%d\n", err);
> @@ -444,6 +475,7 @@ 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 +486,24 @@ static int amd_mdb_pcie_probe(struct platform_device *pdev)
>
> platform_set_drvdata(pdev, pcie);
>
> + ret = amd_mdb_parse_pcie_port(pcie);
> + /*
> + * If amd_mdb_parse_pcie_port returns -ENODEV, it indicates that the
> + * PCIe Bridge node was not found in the device tree. This is not
> + * considered a fatal error and will trigger a fallback where the
> + * reset GPIO is acquired directly from the PCIe Host Bridge node.
> + */
> + if (ret) {
> + if (ret != -ENODEV)
> + return ret;
> +
> + pcie->perst_gpio = devm_gpiod_get_optional(dev, "reset",
> + GPIOD_OUT_HIGH);
> + if (IS_ERR(pcie->perst_gpio))
> + return dev_err_probe(dev, PTR_ERR(pcie->perst_gpio),
> + "Failed to request reset GPIO\n");
> + }
> +
> return amd_mdb_add_pcie_port(pcie, pdev);
> }
>
> --
> 2.43.0
>
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