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, 156 insertions, 0 deletions

diff --git a/drivers/hwmon/max31722.c b/drivers/hwmon/max31722.c
new file mode 100644
index 000000000..6c5c86c75
--- /dev/null
+++ b/drivers/hwmon/max31722.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * max31722 - hwmon driver for Maxim Integrated MAX31722/MAX31723 SPI
+ * digital thermometer and thermostats.
+ *
+ * Copyright (c) 2016, Intel Corporation.
+ */
+
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/sysfs.h>
+
+#define MAX31722_REG_CFG				0x00
+#define MAX31722_REG_TEMP_LSB				0x01
+
+#define MAX31722_MODE_CONTINUOUS			0x00
+#define MAX31722_MODE_STANDBY				0x01
+#define MAX31722_MODE_MASK				0xFE
+#define MAX31722_RESOLUTION_12BIT			0x06
+#define MAX31722_WRITE_MASK				0x80
+
+struct max31722_data {
+	struct device *hwmon_dev;
+	struct spi_device *spi_device;
+	u8 mode;
+};
+
+static int max31722_set_mode(struct max31722_data *data, u8 mode)
+{
+	int ret;
+	struct spi_device *spi = data->spi_device;
+	u8 buf[2] = {
+		MAX31722_REG_CFG | MAX31722_WRITE_MASK,
+		(data->mode & MAX31722_MODE_MASK) | mode
+	};
+
+	ret = spi_write(spi, &buf, sizeof(buf));
+	if (ret < 0) {
+		dev_err(&spi->dev, "failed to set sensor mode.\n");
+		return ret;
+	}
+	data->mode = (data->mode & MAX31722_MODE_MASK) | mode;
+
+	return 0;
+}
+
+static ssize_t max31722_temp_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	ssize_t ret;
+	struct max31722_data *data = dev_get_drvdata(dev);
+
+	ret = spi_w8r16(data->spi_device, MAX31722_REG_TEMP_LSB);
+	if (ret < 0)
+		return ret;
+	/* Keep 12 bits and multiply by the scale of 62.5 millidegrees/bit. */
+	return sysfs_emit(buf, "%d\n", (s16)le16_to_cpu(ret) * 125 / 32);
+}
+
+static SENSOR_DEVICE_ATTR_RO(temp1_input, max31722_temp, 0);
+
+static struct attribute *max31722_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(max31722);
+
+static int max31722_probe(struct spi_device *spi)
+{
+	int ret;
+	struct max31722_data *data;
+
+	data = devm_kzalloc(&spi->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	spi_set_drvdata(spi, data);
+	data->spi_device = spi;
+	/*
+	 * Set SD bit to 0 so we can have continuous measurements.
+	 * Set resolution to 12 bits for maximum precision.
+	 */
+	data->mode = MAX31722_MODE_CONTINUOUS | MAX31722_RESOLUTION_12BIT;
+	ret = max31722_set_mode(data, MAX31722_MODE_CONTINUOUS);
+	if (ret < 0)
+		return ret;
+
+	data->hwmon_dev = hwmon_device_register_with_groups(&spi->dev,
+							    spi->modalias,
+							    data,
+							    max31722_groups);
+	if (IS_ERR(data->hwmon_dev)) {
+		max31722_set_mode(data, MAX31722_MODE_STANDBY);
+		return PTR_ERR(data->hwmon_dev);
+	}
+
+	return 0;
+}
+
+static void max31722_remove(struct spi_device *spi)
+{
+	struct max31722_data *data = spi_get_drvdata(spi);
+	int ret;
+
+	hwmon_device_unregister(data->hwmon_dev);
+
+	ret = max31722_set_mode(data, MAX31722_MODE_STANDBY);
+	if (ret)
+		/* There is nothing we can do about this ... */
+		dev_warn(&spi->dev, "Failed to put device in stand-by mode\n");
+}
+
+static int max31722_suspend(struct device *dev)
+{
+	struct spi_device *spi_device = to_spi_device(dev);
+	struct max31722_data *data = spi_get_drvdata(spi_device);
+
+	return max31722_set_mode(data, MAX31722_MODE_STANDBY);
+}
+
+static int max31722_resume(struct device *dev)
+{
+	struct spi_device *spi_device = to_spi_device(dev);
+	struct max31722_data *data = spi_get_drvdata(spi_device);
+
+	return max31722_set_mode(data, MAX31722_MODE_CONTINUOUS);
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(max31722_pm_ops, max31722_suspend, max31722_resume);
+
+static const struct spi_device_id max31722_spi_id[] = {
+	{"max31722", 0},
+	{"max31723", 0},
+	{}
+};
+MODULE_DEVICE_TABLE(spi, max31722_spi_id);
+
+static struct spi_driver max31722_driver = {
+	.driver = {
+		.name = "max31722",
+		.pm = pm_sleep_ptr(&max31722_pm_ops),
+	},
+	.probe =            max31722_probe,
+	.remove =           max31722_remove,
+	.id_table =         max31722_spi_id,
+};
+
+module_spi_driver(max31722_driver);
+
+MODULE_AUTHOR("Tiberiu Breana <tiberiu.a.breana@intel.com>");
+MODULE_DESCRIPTION("max31722 sensor driver");
+MODULE_LICENSE("GPL v2");