Enabling pmbus power control
Zev Weiss
zev at bewilderbeest.net
Tue Apr 20 17:06:00 AEST 2021
On Tue, Apr 20, 2021 at 01:00:25AM CDT, Guenter Roeck wrote:
>On 4/19/21 10:50 PM, Zev Weiss wrote:
>[ ... ]
>
>> I had a glance at the enclosure driver; it looks pretty geared toward SES-like things (drivers/scsi/ses.c being its only usage I can see in the kernel at the moment) and while it could perhaps be pressed into working for this it seems like it would probably drag in a fair amount of boilerplate and result in a somewhat gratuitously confusing driver arrangement (calling the things involved in the cases we're looking at "enclosures" seems like a bit of a stretch).
>>
>> As an alternative, would something like the patch below be more along the lines of what you're suggesting? And if so, would it make sense to generalize it into something like 'pmbus-switch.c' and add a PMBUS_HAVE_POWERSWITCH functionality bit or similar in the pmbus code instead of hardcoding it for only LM25066 support?
>>
>>
>
>No. Don't access pmbus functions from outside drivers/hwmon/pmbus.
>
>I used to be opposed to function export restrictions (aka export namespaces),
>but you are making a good case that we need to introduce them for pmbus
>functions.
>
>Guenter
Okay -- I figured that was likely to be frowned upon, but the
alternative seemed to be effectively duplicating non-trivial chunks of
the pmbus code. However, upon realizing that the LM25066 doesn't
actually require any of the paging work the generic pmbus code provides,
I suppose it can actually be done with a simple smbus read & write.
Does this version look better?
Zev
From 1662e1c59c498ad6b208e6ab450bd467d71def34 Mon Sep 17 00:00:00 2001
From: Zev Weiss <zev at bewilderbeest.net>
Date: Wed, 31 Mar 2021 01:58:35 -0500
Subject: [PATCH] misc: add lm25066-switch driver
This driver allows an lm25066 to be switched on and off from userspace
via sysfs.
Signed-off-by: Zev Weiss <zev at bewilderbeest.net>
---
drivers/misc/Kconfig | 7 ++
drivers/misc/Makefile | 1 +
drivers/misc/lm25066-switch.c | 126 ++++++++++++++++++++++++++++++++++
3 files changed, 134 insertions(+)
create mode 100644 drivers/misc/lm25066-switch.c
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index f532c59bb59b..384b6022ec15 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -445,6 +445,13 @@ config HISI_HIKEY_USB
switching between the dual-role USB-C port and the USB-A host ports
using only one USB controller.
+config LM25066_SWITCH
+ tristate "LM25066 power switch support"
+ depends on OF && SENSORS_LM25066
+ help
+ This driver augments LM25066 hwmon support with power switch
+ functionality controllable from userspace via sysfs.
+
source "drivers/misc/c2port/Kconfig"
source "drivers/misc/eeprom/Kconfig"
source "drivers/misc/cb710/Kconfig"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 99b6f15a3c70..c948510d0cc9 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -56,3 +56,4 @@ obj-$(CONFIG_HABANA_AI) += habanalabs/
obj-$(CONFIG_UACCE) += uacce/
obj-$(CONFIG_XILINX_SDFEC) += xilinx_sdfec.o
obj-$(CONFIG_HISI_HIKEY_USB) += hisi_hikey_usb.o
+obj-$(CONFIG_LM25066_SWITCH) += lm25066-switch.o
diff --git a/drivers/misc/lm25066-switch.c b/drivers/misc/lm25066-switch.c
new file mode 100644
index 000000000000..9adc67c320f9
--- /dev/null
+++ b/drivers/misc/lm25066-switch.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This module provides a thin wrapper around the lm25066 hwmon driver that
+ * additionally exposes a userspace-controllable on/off power switch via
+ * sysfs.
+ *
+ * Author: Zev Weiss <zweiss at equinix.com>
+ *
+ * Copyright (C) 2021 Equinix Services, Inc.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/i2c.h>
+#include <linux/platform_device.h>
+
+/*
+ * The relevant PMBus command and data values for controlling the LM25066
+ * power state. Because it's not a paged device we skip the usual paging
+ * business other PMBus devices might require.
+ */
+#define CMD_OPERATION 0x01
+#define OPERATION_ON 0x80
+#define OPERATION_OFF 0x00
+
+static ssize_t switch_show_state(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct i2c_client *pmic = dev_get_drvdata(dev);
+ ssize_t ret = i2c_smbus_read_byte_data(pmic, CMD_OPERATION);
+ if (ret < 0)
+ return ret;
+
+ return sysfs_emit(buf, "%s\n", (ret & OPERATION_ON) ? "on" : "off");
+}
+
+static ssize_t switch_set_state(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ int status;
+ u8 value;
+ struct i2c_client *pmic = dev_get_drvdata(dev);
+ if (sysfs_streq(buf, "on"))
+ value = OPERATION_ON;
+ else if (sysfs_streq(buf, "off"))
+ value = OPERATION_OFF;
+ else
+ return -EINVAL;
+ status = i2c_smbus_write_byte_data(pmic, CMD_OPERATION, value);
+ return status ? : count;
+}
+
+static DEVICE_ATTR(state, 0644, switch_show_state, switch_set_state);
+
+static struct attribute *attributes[] = {
+ &dev_attr_state.attr,
+ NULL,
+};
+
+static const struct attribute_group attr_group = {
+ .attrs = attributes,
+};
+
+static int lm25066_switch_probe(struct platform_device *pdev)
+{
+ int status;
+ struct device_node *np = pdev->dev.of_node;
+ struct device_node *pmic_np;
+ struct i2c_client *pmic;
+
+ pmic_np = of_parse_phandle(np, "pmic", 0);
+ if (!pmic_np) {
+ dev_err(&pdev->dev, "Cannot parse lm25066-switch pmic\n");
+ return -ENODEV;
+ }
+
+ if (!of_device_is_compatible(pmic_np, "lm25066")) {
+ dev_err(&pdev->dev, "lm25066-switch pmic not lm25066 compatible");
+ status = -ENODEV;
+ goto out;
+ }
+
+ pmic = of_find_i2c_device_by_node(pmic_np);
+ if (!pmic) {
+ status = -EPROBE_DEFER;
+ goto out;
+ }
+
+ platform_set_drvdata(pdev, pmic);
+
+ status = sysfs_create_group(&pdev->dev.kobj, &attr_group);
+
+out:
+ of_node_put(pmic_np);
+ return status;
+}
+
+static int lm25066_switch_remove(struct platform_device *pdev)
+{
+ struct i2c_client *pmic = platform_get_drvdata(pdev);
+
+ sysfs_remove_group(&pdev->dev.kobj, &attr_group);
+ put_device(&pmic->dev);
+
+ return 0;
+}
+
+static const struct of_device_id lm25066_switch_table[] = {
+ { .compatible = "lm25066-switch" },
+ { },
+};
+
+static struct platform_driver lm25066_switch_driver = {
+ .driver = {
+ .name = "lm25066-switch",
+ .of_match_table = lm25066_switch_table,
+ },
+ .probe = lm25066_switch_probe,
+ .remove = lm25066_switch_remove,
+};
+
+module_platform_driver(lm25066_switch_driver);
+
+MODULE_AUTHOR("Zev Weiss <zweiss at equinix.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("LM25066 power-switch driver");
--
2.31.1
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