Re: [RFC PATCH] soc: aspeed: Add B650D4U power passthrough support

From: Tan Siewert

Date: Fri Oct 02 2026 - 12:51:10 EST

On 10/2/26 3:16 PM, Prasanth Kumar Padarthi wrote:

Add the AST2600 SCU passthrough selector support used by the
ASRock Rack B650D4U host power-control circuit. This RFC includes
the driver, Devicetree binding, and board node to discuss the final
kernel-facing interface.

Signed-off-by: Prasanth Kumar Padarthi <prasanth.padarthi10@xxxxxxxxx>

This is definitely not the way how to solve this. I've already said on linux-aspeed as well as off-the-list, requesting the GPIO lines is enough and enabling GPIOP passthrough here does not make any sense, as it would be disabled by pinctrl anyways.
There's a whole implementation in userspace to solve this issue (at least if you use OpenBMC). The issue you're facing here is, from my point of view, a configuration error, and you'll not solve it with a kernel driver that literally just enables GPIOP passthrough...

So my answer to this patch is:
NACKed-by: Tan Siewert <tan.siewert@xxxxxxxxxxxxx>

---
.../asrock,b650d4u-power-passthrough.yaml | 23 ++++
.../dts/aspeed/aspeed-bmc-asrock-b650d4u.dts | 5 +
drivers/soc/aspeed/Kconfig | 9 ++
drivers/soc/aspeed/Makefile | 1 +
drivers/soc/aspeed/aspeed-b650d4u-power.c | 110 ++++++++++++++++++
5 files changed, 148 insertions(+)
create mode 100644 Documentation/devicetree/bindings/soc/aspeed/asrock,b650d4u-power-passthrough.yaml
create mode 100644 drivers/soc/aspeed/aspeed-b650d4u-power.c

diff --git a/Documentation/devicetree/bindings/soc/aspeed/asrock,b650d4u-power-passthrough.yaml b/Documentation/devicetree/bindings/soc/aspeed/asrock,b650d4u-power-passthrough.yaml
new file mode 100644
index 000000000000..e6451d17955c
--- /dev/null
+++ b/Documentation/devicetree/bindings/soc/aspeed/asrock,b650d4u-power-passthrough.yaml
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/soc/aspeed/asrock,b650d4u-power-passthrough.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ASRock Rack B650D4U power passthrough
+
+maintainers:
+ - Prasanth Kumar Padarthi <prasanth.padarthi10@xxxxxxxxx>
+
+properties:
+ compatible:
+ const: asrock,b650d4u-power-passthrough
+
+ aspeed,scu:
+ $ref: /schemas/types.yaml#/definitions/phandle
+
+required:
+ - compatible
+ - aspeed,scu
+
+additionalProperties: false
diff --git a/arch/arm/boot/dts/aspeed/aspeed-bmc-asrock-b650d4u.dts b/arch/arm/boot/dts/aspeed/aspeed-bmc-asrock-b650d4u.dts
index a4e384588a54..86291c250562 100644
--- a/arch/arm/boot/dts/aspeed/aspeed-bmc-asrock-b650d4u.dts
+++ b/arch/arm/boot/dts/aspeed/aspeed-bmc-asrock-b650d4u.dts
@@ -32,6 +32,11 @@ gfx_memory: framebuffer {
size = <0x01000000>;
};
};
+
+ host-power-passthrough {
+ compatible = "asrock,b650d4u-power-passthrough";
+ aspeed,scu = <&syscon>;
+ };
};
&fmc {
diff --git a/drivers/soc/aspeed/Kconfig b/drivers/soc/aspeed/Kconfig
index 11e4db998c06..1b0281e0bfb0 100644
--- a/drivers/soc/aspeed/Kconfig
+++ b/drivers/soc/aspeed/Kconfig
@@ -58,6 +58,15 @@ config ASPEED_SBC
Say yes to provide information about the secure boot controller in
debugfs.
+config ASPEED_B650D4U_POWER
+ tristate "ASRock B650D4U host power passthrough"
+ select REGMAP
+ select MFD_SYSCON
+ default ARCH_ASPEED
+ help
+ Enable the AST2600 GPIO passthrough selector used by the
+ ASRock Rack B650D4U host power-control circuit. This selector routes the host power pulse through the board's passthrough logic during power sequencing.
+
config ASPEED_XDMA
tristate "ASPEED XDMA Engine Driver"
select REGMAP
diff --git a/drivers/soc/aspeed/Makefile b/drivers/soc/aspeed/Makefile
index 5f61bb4cc36c..3e9618d1eafc 100644
--- a/drivers/soc/aspeed/Makefile
+++ b/drivers/soc/aspeed/Makefile
@@ -5,4 +5,5 @@ obj-$(CONFIG_ASPEED_UART_ROUTING) += aspeed-uart-routing.o
obj-$(CONFIG_ASPEED_P2A_CTRL) += aspeed-p2a-ctrl.o
obj-$(CONFIG_ASPEED_SOCINFO) += aspeed-socinfo.o
obj-$(CONFIG_ASPEED_SBC) += aspeed-sbc.o
+obj-$(CONFIG_ASPEED_B650D4U_POWER) += aspeed-b650d4u-power.o
obj-$(CONFIG_ASPEED_XDMA) += aspeed-xdma.o
diff --git a/drivers/soc/aspeed/aspeed-b650d4u-power.c b/drivers/soc/aspeed/aspeed-b650d4u-power.c
new file mode 100644
index 000000000000..22a6925539dc
--- /dev/null
+++ b/drivers/soc/aspeed/aspeed-b650d4u-power.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mfd/syscon.h>
+#include <linux/mutex.h>
+#include <linux/kstrtox.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/bits.h>
+
+#define ASPEED_SCU_PROTECTION 0x000
+#define ASPEED_SCU_GPIO_PASSTHROUGH 0x4bc
+#define ASPEED_SCU_GPIO_ACTION 0x51c
+#define ASPEED_SCU_UNLOCK_KEY 0x1688a8a8
+#define ASPEED_B650D4U_POWER_MASK GENMASK(27, 26)
+
+static struct regmap *b650d4u_scu;
+static DEFINE_MUTEX(b650d4u_lock);
+
+static int b650d4u_set_passthrough(bool enable)
+{
+ int ret;
+
+ mutex_lock(&b650d4u_lock);
+
+ ret = regmap_write(b650d4u_scu, ASPEED_SCU_PROTECTION,
+ ASPEED_SCU_UNLOCK_KEY);
+ if (ret) {
+ pr_err("B650D4U: SCU unlock failed: %d\n", ret);
+ goto out;
+ }
+
+ ret = regmap_update_bits(b650d4u_scu,
+ ASPEED_SCU_GPIO_PASSTHROUGH,
+ ASPEED_B650D4U_POWER_MASK,
+ enable ? ASPEED_B650D4U_POWER_MASK : 0);
+ if (ret) {
+ pr_err("B650D4U: passthrough update failed: %d\n", ret);
+ goto out;
+ }
+
+ if (!enable)
+ ret = regmap_write(b650d4u_scu,
+ ASPEED_SCU_GPIO_ACTION, 0);
+
+out:
+ mutex_unlock(&b650d4u_lock);
+ return ret;
+}
+
+static ssize_t passthrough_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ bool enable;
+ int ret;
+
+ ret = kstrtobool(buf, &enable);
+ if (ret)
+ return ret;
+
+ ret = b650d4u_set_passthrough(enable);
+ return ret ? ret : count;
+}
+static DEVICE_ATTR_WO(passthrough);
+
+static int aspeed_b650d4u_power_probe(struct platform_device *pdev)
+{
+ int ret;
+
+ b650d4u_scu = syscon_regmap_lookup_by_phandle(pdev->dev.of_node,
+ "aspeed,scu");
+ if (IS_ERR(b650d4u_scu))
+ return dev_err_probe(&pdev->dev, PTR_ERR(b650d4u_scu),
+ "failed to get AST2600 SCU regmap\n");
+
+ ret = b650d4u_set_passthrough(true);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "failed to enable power GPIO passthrough\n");
+
+ ret = device_create_file(&pdev->dev, &dev_attr_passthrough);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "failed to create passthrough control\n");
+
+ dev_info(&pdev->dev, "enabled GPIO passthrough selector 1\n");
+ return 0;
+}
+
+static const struct of_device_id aspeed_b650d4u_power_of_match[] = {
+ { .compatible = "asrock,b650d4u-power-passthrough" },
+ { }
+};
+MODULE_DEVICE_TABLE(of, aspeed_b650d4u_power_of_match);
+
+static struct platform_driver aspeed_b650d4u_power_driver = {
+ .probe = aspeed_b650d4u_power_probe,
+ .driver = {
+ .name = "aspeed-b650d4u-power",
+ .of_match_table = aspeed_b650d4u_power_of_match,
+ },
+};
+module_platform_driver(aspeed_b650d4u_power_driver);
+
+MODULE_DESCRIPTION("ASRock Rack B650D4U host power GPIO passthrough");
+MODULE_LICENSE("GPL");