KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 172 insertions, 0 deletions

diff --git a/drivers/hwmon/tc74.c b/drivers/hwmon/tc74.c
new file mode 100644
index 000000000..e9113519b
--- /dev/null
+++ b/drivers/hwmon/tc74.c
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * An hwmon driver for the Microchip TC74
+ *
+ * Copyright 2015 Maciej Szmigiero <mail@maciej.szmigiero.name>
+ *
+ * Based on ad7414.c:
+ *	Copyright 2006 Stefan Roese, DENX Software Engineering
+ *	Copyright 2008 Sean MacLennan, PIKA Technologies
+ *	Copyright 2008 Frank Edelhaeuser, Spansion Inc.
+ */
+
+#include <linux/bitops.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/i2c.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+
+/* TC74 registers */
+#define TC74_REG_TEMP		0x00
+#define TC74_REG_CONFIG		0x01
+
+struct tc74_data {
+	struct i2c_client	*client;
+	struct mutex		lock;	/* atomic read data updates */
+	bool			valid;	/* validity of fields below */
+	unsigned long		next_update;	/* In jiffies */
+	s8			temp_input;	/* Temp value in dC */
+};
+
+static int tc74_update_device(struct device *dev)
+{
+	struct tc74_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+	int ret;
+
+	ret = mutex_lock_interruptible(&data->lock);
+	if (ret)
+		return ret;
+
+	if (time_after(jiffies, data->next_update) || !data->valid) {
+		s32 value;
+
+		value = i2c_smbus_read_byte_data(client, TC74_REG_CONFIG);
+		if (value < 0) {
+			dev_dbg(&client->dev, "TC74_REG_CONFIG read err %d\n",
+				(int)value);
+
+			ret = value;
+			goto ret_unlock;
+		}
+
+		if (!(value & BIT(6))) {
+			/* not ready yet */
+
+			ret = -EAGAIN;
+			goto ret_unlock;
+		}
+
+		value = i2c_smbus_read_byte_data(client, TC74_REG_TEMP);
+		if (value < 0) {
+			dev_dbg(&client->dev, "TC74_REG_TEMP read err %d\n",
+				(int)value);
+
+			ret = value;
+			goto ret_unlock;
+		}
+
+		data->temp_input = value;
+		data->next_update = jiffies + HZ / 4;
+		data->valid = true;
+	}
+
+ret_unlock:
+	mutex_unlock(&data->lock);
+
+	return ret;
+}
+
+static ssize_t temp_input_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct tc74_data *data = dev_get_drvdata(dev);
+	int ret;
+
+	ret = tc74_update_device(dev);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%d\n", data->temp_input * 1000);
+}
+static SENSOR_DEVICE_ATTR_RO(temp1_input, temp_input, 0);
+
+static struct attribute *tc74_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(tc74);
+
+static int tc74_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct tc74_data *data;
+	struct device *hwmon_dev;
+	s32 conf;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+		return -EOPNOTSUPP;
+
+	data = devm_kzalloc(dev, sizeof(struct tc74_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	mutex_init(&data->lock);
+
+	/* Make sure the chip is powered up. */
+	conf = i2c_smbus_read_byte_data(client, TC74_REG_CONFIG);
+	if (conf < 0) {
+		dev_err(dev, "unable to read config register\n");
+
+		return conf;
+	}
+
+	if (conf & 0x3f) {
+		dev_err(dev, "invalid config register value\n");
+
+		return -ENODEV;
+	}
+
+	if (conf & BIT(7)) {
+		s32 ret;
+
+		conf &= ~BIT(7);
+
+		ret = i2c_smbus_write_byte_data(client, TC74_REG_CONFIG, conf);
+		if (ret)
+			dev_warn(dev, "unable to disable STANDBY\n");
+	}
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(dev,
+							   client->name,
+							   data, tc74_groups);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id tc74_id[] = {
+	{ .name = "tc74" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, tc74_id);
+
+static struct i2c_driver tc74_driver = {
+	.driver = {
+		.name	= "tc74",
+	},
+	.probe = tc74_probe,
+	.id_table = tc74_id,
+};
+
+module_i2c_driver(tc74_driver);
+
+MODULE_AUTHOR("Maciej Szmigiero <mail@maciej.szmigiero.name>");
+
+MODULE_DESCRIPTION("TC74 driver");
+MODULE_LICENSE("GPL");