[RFC PATCH] soc: aspeed: Add B650D4U power passthrough support
Tan Siewert
tan.siewert at 9elements.com
Fri Oct 2 09:47:09 PDT 2026
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 at gmail.com>
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 at 9elements.com>
> ---
> .../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 at gmail.com>
> +
> +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");
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