Add Hasivo STC8 multi-function device (syscon)

Performs register passthrough with added OR'ing of execute bit if required.

Signed-off-by: Bevan Weiss <[email protected]>

Author: bevanweiss

target/linux/generic/files/Documentation/devicetree/bindings/mfd/hasivo,stc8-mfd.yaml

@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: GPL-2.0
+# STC8 MFD binding for Hasivo switches
+# Defines properties for MFD regmap wrapper, LEDs, and PWM
+
+title: "STC8 multi-function device"
+description: |
+  This binding describes the Hasivo STC8 multi-function device.
+  This is an STC8 microcontroller with custom firmware used by Hasivo to
+  provide various functions on their managed switch products.
+  The main known functionality currently is to allow for discrete GPIO control
+  which turns on/off LEDs and controls PWM for fan speed.
+  It is known that for the discrete IO however, the host must send an execute
+  flag (0x40) along with the register write to have the STC8 apply the change.
+  This binding allows for specifying which registers require this execute flag
+  to be set automatically by the MFD driver.
+
+maintainers:
+  - [email protected]
+
+properties:
+  compatible:
+    description: >
+      Must be "hasivo,stc8" for the MFD driver to bind.
+    type: string
+    required: true
+
+  reg:
+    description: >
+      I2C address of the STC8 device.
+    type: array of integers
+    required: true
+
+  reg-names:
+    description: >
+      Names of register blocks for the device.
+    type: array of strings
+    required: true
+
+  hasivo,execute-bit-regs:
+    description: >
+      Array of registers for which the execute-bit (0x40) should be
+      automatically ORed on writes.
+    type: array of integers
+    required: false
+
+children:
+  

target/linux/generic/files/drivers/mfd/hasivo-stc8-mfd.c

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/of_platform.h>
+#include <linux/mfd/syscon.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+struct stc8_hook {
+    struct regmap *orig_map;
+    int (*orig_write)(struct regmap *, unsigned int, unsigned int);
+    u8 *execute_regs;
+    int execute_count;
+};
+
+struct stc8_mfd {
+    struct device *dev;
+    struct regmap *regmap;
+    struct stc8_hook *hook;
+};
+
+/* Hooked regmap_write */
+static int stc8_hooked_write(struct regmap *map, unsigned int reg, unsigned int val)
+{
+    struct stc8_hook *hook = map->regmap_volatile_context;
+    unsigned int new_val = val;
+
+    /* OR execute bit if reg matches DT list */
+    for (int i = 0; i < hook->execute_count; i++) {
+        if (reg == hook->execute_regs[i]) {
+            new_val |= 0x40;
+            break;
+        }
+    }
+
+    pr_info("%s: STC8 MFD write intercepted, reg=0x%x, orig_val=0x%x, new_val=0x%x\n", __func__, reg, val, new_val);
+    /* Call original write */
+    return hook->orig_write(hook->orig_map, reg, new_val);
+}
+
+static int stc8_mfd_probe(struct platform_device *pdev)
+{
+    struct device_node *np = pdev->dev.of_node;
+    struct stc8_mfd *mfd;
+    struct regmap *parent_map;
+    const __be32 *regs;
+    int count, i, ret;
+
+    mfd = devm_kzalloc(&pdev->dev, sizeof(*mfd), GFP_KERNEL);
+    if (!mfd)
+        return -ENOMEM;
+    mfd->dev = &pdev->dev;
+
+    /* Get parent syscon regmap */
+    parent_map = syscon_node_to_regmap(np);
+    if (IS_ERR(parent_map))
+        return PTR_ERR(parent_map);
+
+    mfd->regmap = parent_map;
+
+    /* Parse DT execute-bit registers */
+    regs = of_get_property(np, "hasivo,execute-bit-regs", &count);
+    if (!regs || count < 0)
+        return -EINVAL;
+
+    count /= sizeof(u32);
+    mfd->hook = devm_kzalloc(&pdev->dev, sizeof(*mfd->hook), GFP_KERNEL);
+    if (!mfd->hook)
+        return -ENOMEM;
+
+    mfd->hook->orig_map = parent_map;
+    mfd->hook->orig_write = parent_map->regmap_write;
+    mfd->hook->execute_count = count;
+    mfd->hook->execute_regs = count > 0 ? devm_kmalloc(&pdev->dev, count, GFP_KERNEL) : NULL;
+    if (!mfd->hook->execute_regs)
+        return -ENOMEM;
+
+    for (i = 0; i < count; i++)
+        mfd->hook->execute_regs[i] = be32_to_cpup(regs + i);
+
+    /* Overwrite parent regmap write pointer */
+    parent_map->regmap_write = stc8_hooked_write;
+    parent_map->regmap_volatile_context = mfd->hook;  // hook context
+
+    /* Populate children (LEDs, PWM, etc) - children will use parent regmap */
+    ret = of_platform_populate(np, NULL, NULL, &pdev->dev);
+    if (ret) {
+        dev_err(&pdev->dev, "Failed to populate child devices\n");
+        return ret;
+    }
+
+    dev_info(&pdev->dev, "STC8 MFD probe complete, execute-bit hooked\n");
+    return 0;
+}
+
+static const struct of_device_id stc8_mfd_of_match[] = {
+    { .compatible = "hasivo,stc8-mfd" },
+    { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, stc8_mfd_of_match);
+
+static struct platform_driver stc8_mfd_driver = {
+    .driver = {
+        .name = "stc8-mfd",
+        .of_match_table = stc8_mfd_of_match,
+    },
+    .probe = stc8_mfd_probe,
+};
+module_platform_driver(stc8_mfd_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("STC8 MFD driver with regmap-write hook for execute-bit");
+MODULE_AUTHOR("Bevan Weiss <[email protected]>");

target/linux/generic/pending-6.12/362-add-hasivo-stc8-mfd.patch

@@ -0,0 +1,38 @@
+
+
+--- a/drivers/mfd/Kconfig
++++ b/drivers/mfd/Kconfig
+@@ -540,10 +540,21 @@
+config MFD_MX25_TSADC
+	tristate "Freescale i.MX25 integrated Touchscreen and ADC unit"
+	select REGMAP_MMIO
+	depends on (SOC_IMX25 && OF) || COMPILE_TEST
+	help
+	  Enable support for the integrated Touchscreen and ADC unit of the
+	  i.MX25 processors. They consist of a conversion queue for general
+	  purpose ADC and a queue for Touchscreens.
++
++config MFD_HASIVO_STC8
++	tristate "Hasivo STC8 Multifunction Device"
++	select MFD_CORE
++	select REGMAP_I2C
++	depends on I2C
++	help
++	  Support for the Hasivo STC8 multifunction device over I2C.
++	  This driver provides common support for accessing the device,
++	  additional drivers must be enabled in order to use the
++	  functionality of the device.
+
+config MFD_HI6421_PMIC
+
+
+---
+--- a/drivers/mfd/Makefile
++++ b/drivers/mfd/Makefile
+@@ -291,2 +291,4 @@
+obj-$(CONFIG_MFD_RSMU_I2C)	+= rsmu_i2c.o rsmu_core.o
+obj-$(CONFIG_MFD_RSMU_SPI)	+= rsmu_spi.o rsmu_core.o
++
++obj-$(CONFIG_MFD_HASIVO_STC8)	+= hasivo-stc8-mfd.o
+
+