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, 147 insertions, 0 deletions

diff --git a/drivers/hwmon/kbatt.c b/drivers/hwmon/kbatt.c
new file mode 100644
index 000000000..501b8f4de
--- /dev/null
+++ b/drivers/hwmon/kbatt.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 KEBA Industrial Automation GmbH
+ *
+ * Driver for KEBA battery monitoring controller FPGA IP core
+ */
+
+#include <linux/hwmon.h>
+#include <linux/io.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/auxiliary_bus.h>
+#include <linux/misc/keba.h>
+#include <linux/mutex.h>
+
+#define KBATT "kbatt"
+
+#define KBATT_CONTROL_REG		0x4
+#define   KBATT_CONTROL_BAT_TEST	0x01
+
+#define KBATT_STATUS_REG		0x8
+#define   KBATT_STATUS_BAT_OK		0x01
+
+#define KBATT_MAX_UPD_INTERVAL	(10 * HZ)
+#define KBATT_SETTLE_TIME_US	(100 * USEC_PER_MSEC)
+
+struct kbatt {
+	/* update lock */
+	struct mutex lock;
+	void __iomem *base;
+
+	unsigned long next_update; /* in jiffies */
+	bool alarm;
+};
+
+static bool kbatt_alarm(struct kbatt *kbatt)
+{
+	mutex_lock(&kbatt->lock);
+
+	if (!kbatt->next_update || time_after(jiffies, kbatt->next_update)) {
+		/* switch load on */
+		iowrite8(KBATT_CONTROL_BAT_TEST,
+			 kbatt->base + KBATT_CONTROL_REG);
+
+		/* wait some time to let things settle */
+		fsleep(KBATT_SETTLE_TIME_US);
+
+		/* check battery state */
+		if (ioread8(kbatt->base + KBATT_STATUS_REG) &
+		    KBATT_STATUS_BAT_OK)
+			kbatt->alarm = false;
+		else
+			kbatt->alarm = true;
+
+		/* switch load off */
+		iowrite8(0, kbatt->base + KBATT_CONTROL_REG);
+
+		kbatt->next_update = jiffies + KBATT_MAX_UPD_INTERVAL;
+	}
+
+	mutex_unlock(&kbatt->lock);
+
+	return kbatt->alarm;
+}
+
+static int kbatt_read(struct device *dev, enum hwmon_sensor_types type,
+		      u32 attr, int channel, long *val)
+{
+	struct kbatt *kbatt = dev_get_drvdata(dev);
+
+	*val = kbatt_alarm(kbatt) ? 1 : 0;
+
+	return 0;
+}
+
+static umode_t kbatt_is_visible(const void *data, enum hwmon_sensor_types type,
+				u32 attr, int channel)
+{
+	if (channel == 0 && attr == hwmon_in_min_alarm)
+		return 0444;
+
+	return 0;
+}
+
+static const struct hwmon_channel_info *kbatt_info[] = {
+	HWMON_CHANNEL_INFO(in,
+			   /* 0: input minimum alarm channel */
+			   HWMON_I_MIN_ALARM),
+	NULL
+};
+
+static const struct hwmon_ops kbatt_hwmon_ops = {
+	.is_visible = kbatt_is_visible,
+	.read = kbatt_read,
+};
+
+static const struct hwmon_chip_info kbatt_chip_info = {
+	.ops = &kbatt_hwmon_ops,
+	.info = kbatt_info,
+};
+
+static int kbatt_probe(struct auxiliary_device *auxdev,
+		       const struct auxiliary_device_id *id)
+{
+	struct keba_batt_auxdev *kbatt_auxdev =
+		container_of(auxdev, struct keba_batt_auxdev, auxdev);
+	struct device *dev = &auxdev->dev;
+	struct device *hwmon_dev;
+	struct kbatt *kbatt;
+	int retval;
+
+	kbatt = devm_kzalloc(dev, sizeof(*kbatt), GFP_KERNEL);
+	if (!kbatt)
+		return -ENOMEM;
+
+	retval = devm_mutex_init(dev, &kbatt->lock);
+	if (retval)
+		return retval;
+
+	kbatt->base = devm_ioremap_resource(dev, &kbatt_auxdev->io);
+	if (IS_ERR(kbatt->base))
+		return PTR_ERR(kbatt->base);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, KBATT, kbatt,
+							 &kbatt_chip_info,
+							 NULL);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct auxiliary_device_id kbatt_devtype_aux[] = {
+	{ .name = "keba.batt" },
+	{}
+};
+MODULE_DEVICE_TABLE(auxiliary, kbatt_devtype_aux);
+
+static struct auxiliary_driver kbatt_driver_aux = {
+	.name = KBATT,
+	.id_table = kbatt_devtype_aux,
+	.probe = kbatt_probe,
+};
+module_auxiliary_driver(kbatt_driver_aux);
+
+MODULE_AUTHOR("Petar Bojanic <boja@keba.com>");
+MODULE_AUTHOR("Gerhard Engleder <eg@keba.com>");
+MODULE_DESCRIPTION("KEBA battery monitoring controller driver");
+MODULE_LICENSE("GPL");