Re: [PATCH v25 04/10] firmware: psci: Add support for PSCI auxiliary devices

PSCI has multiple kernel consumers, such as cpuidle-psci-domain.
Currently, both the PSCI core driver and cpuidle-psci-domain bind
directly to the same PSCI node "arm,psci-1.0". Additional consumers, if
introduced, would also need to bind in the same way, leading to multiple
drivers attached to a single device node.

Introduce a PSCI auxiliary-device provider that binds to "arm,psci-1.0"
and registers PSCI child devices on the auxiliary bus. As the first
user, register cpuidle-psci-domain as an auxiliary device.

Update cpuidle-psci-domain to probe as an auxiliary driver and use
the PSCI device node for power-domain traversal.

Suggested-by: Ulf Hansson <redacted>
Suggested-by: Lee Jones <lee@kernel.org>
Suggested-by: Bartosz Golaszewski <redacted>
Signed-off-by: Shivendra Pratap <redacted>
---
 MAINTAINERS                           |  1 +
 drivers/cpuidle/Kconfig.arm           |  1 +
 drivers/cpuidle/cpuidle-psci-domain.c | 31 +++++++++++++++-----------
 drivers/firmware/psci/Kconfig         | 14 ++++++++++++
 drivers/firmware/psci/Makefile        |  1 +
 drivers/firmware/psci/psci-devices.c  | 41 +++++++++++++++++++++++++++++++++++
 6 files changed, 76 insertions(+), 13 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 207a6e2db70c..9c0334ee2ed2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -21932,6 +21932,7 @@ L:      linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:     Maintained
 F:     Documentation/devicetree/bindings/arm/psci.yaml
 F:     drivers/firmware/psci/
+F:     drivers/firmware/psci/psci-devices.c
 F:     include/linux/psci.h
 F:     include/uapi/linux/psci.h

diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm
index b88b01aa5829..f22e18b05053 100644
--- a/drivers/cpuidle/Kconfig.arm
+++ b/drivers/cpuidle/Kconfig.arm

@@ -36,6 +36,7 @@ config ARM_PSCI_CPUIDLE_DOMAIN
        bool "PSCI CPU idle Domain"
        depends on ARM_PSCI_CPUIDLE
        depends on PM_GENERIC_DOMAINS_OF
+       depends on ARM_PSCI_DEVICES
        select DT_IDLE_GENPD
        default y
        help

diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
index b9e4ad7d43a3..0ce6a83f6588 100644
--- a/drivers/cpuidle/cpuidle-psci-domain.c
+++ b/drivers/cpuidle/cpuidle-psci-domain.c

@@ -9,10 +9,11 @@

 #define pr_fmt(fmt) "CPUidle PSCI: " fmt

+#include <linux/auxiliary_bus.h>
 #include <linux/cpu.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
-#include <linux/platform_device.h>
+#include <linux/module.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_runtime.h>
 #include <linux/psci.h>

@@ -122,14 +123,10 @@ static void psci_pd_remove(void)
        }
 }

-static const struct of_device_id psci_of_match[] = {
-       { .compatible = "arm,psci-1.0" },
-       {}
-};
-
-static int psci_cpuidle_domain_probe(struct platform_device *pdev)
+static int psci_cpuidle_domain_probe(struct auxiliary_device *auxdev,
+                                    const struct auxiliary_device_id *id)
 {
-       struct device_node *np = pdev->dev.of_node;
+       struct device_node *np = auxdev->dev.of_node;
        bool use_osi = psci_has_osi_support();
        int ret = 0, pd_count = 0;

@@ -177,16 +174,24 @@ static int psci_cpuidle_domain_probe(struct platform_device *pdev)
        return ret;
 }

-static struct platform_driver psci_cpuidle_domain_driver = {
-       .probe  = psci_cpuidle_domain_probe,
+static const struct auxiliary_device_id psci_cpuidle_domain_id_table[] = {
+       { .name = "arm-psci.psci-cpuidle-domain" },
+       { }
+};
+MODULE_DEVICE_TABLE(auxiliary, psci_cpuidle_domain_id_table);
+
+static struct auxiliary_driver psci_cpuidle_domain_driver = {
+       .probe = psci_cpuidle_domain_probe,
        .driver = {
-               .name = "psci-cpuidle-domain",
-               .of_match_table = psci_of_match,
+               .suppress_bind_attrs = true,
        },
+       .id_table = psci_cpuidle_domain_id_table,
 };

 static int __init psci_idle_init_domains(void)
 {
-       return platform_driver_register(&psci_cpuidle_domain_driver);
+       return __auxiliary_driver_register(&psci_cpuidle_domain_driver,
+                                          THIS_MODULE,
+                                          "psci-cpuidle-domain");
 }
 core_initcall(psci_idle_init_domains);

diff --git a/drivers/firmware/psci/Kconfig b/drivers/firmware/psci/Kconfig
index 97944168b5e6..68e381f1a618 100644
--- a/drivers/firmware/psci/Kconfig
+++ b/drivers/firmware/psci/Kconfig

@@ -2,6 +2,20 @@
 config ARM_PSCI_FW
        bool

+config ARM_PSCI_DEVICES
+       bool "PSCI auxiliary device support"
+       depends on ARM_PSCI_FW
+       depends on OF
+       select AUXILIARY_BUS
+       default y
+       help
+         Say Y here to enable auxiliary device support for PSCI.
+
+         This creates auxiliary devices for PSCI functionality implemented
+         outside the core PSCI firmware driver. These devices allow PSCI
+         child drivers to bind through the auxiliary bus while sharing the
+         PSCI firmware device as their parent.
+
 config ARM_PSCI_CHECKER
        bool "ARM PSCI checker"
        depends on ARM_PSCI_FW && HOTPLUG_CPU && CPU_IDLE && !TORTURE_TEST

diff --git a/drivers/firmware/psci/Makefile b/drivers/firmware/psci/Makefile
index 1956b882470f..8e75a0ed6f74 100644
--- a/drivers/firmware/psci/Makefile
+++ b/drivers/firmware/psci/Makefile

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 #
 obj-$(CONFIG_ARM_PSCI_FW)      += psci.o
+obj-$(CONFIG_ARM_PSCI_DEVICES) += psci-devices.o
 obj-$(CONFIG_ARM_PSCI_CHECKER) += psci_checker.o

diff --git a/drivers/firmware/psci/psci-devices.c b/drivers/firmware/psci/psci-devices.c
new file mode 100644
index 000000000000..f1eca61e3269
--- /dev/null
+++ b/drivers/firmware/psci/psci-devices.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#include <linux/auxiliary_bus.h>
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+static int arm_psci_probe(struct platform_device *pdev)
+{
+       struct auxiliary_device *auxdev;
+
+       auxdev = __devm_auxiliary_device_create(&pdev->dev, "arm-psci",
+                                               "psci-cpuidle-domain", NULL, 0);
+       if (!auxdev)
+               return -ENOMEM;
+
+       return 0;
+}
+
+static const struct of_device_id arm_psci_of_match[] = {
+       { .compatible = "arm,psci-1.0" },
+       { }
+};
+
+static struct platform_driver arm_psci_driver = {
+       .probe = arm_psci_probe,
+       .driver = {
+               .name = "arm-psci",
+               .of_match_table = arm_psci_of_match,
+               .suppress_bind_attrs = true,
+       },
+};
+
+static int __init arm_psci_init(void)
+{
+       return platform_driver_register(&arm_psci_driver);
+}
+core_initcall(arm_psci_init);