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, 119 insertions, 0 deletions

diff --git a/drivers/mfd/rt4831.c b/drivers/mfd/rt4831.c
new file mode 100644
index 000000000..1ab8870e4
--- /dev/null
+++ b/drivers/mfd/rt4831.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2021 Richtek Technology Corp.
+ *
+ * Author: ChiYuan Huang <cy_huang@richtek.com>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+
+#define RT4831_REG_REVISION	0x01
+#define RT4831_REG_ENABLE	0x08
+#define RT4831_REG_I2CPROT	0x15
+
+#define RICHTEK_VENDOR_ID	0x03
+#define RT4831_VID_MASK		GENMASK(1, 0)
+#define RT4831_RESET_MASK	BIT(7)
+#define RT4831_I2CSAFETMR_MASK	BIT(0)
+
+static const struct mfd_cell rt4831_subdevs[] = {
+	MFD_CELL_OF("rt4831-backlight", NULL, NULL, 0, 0, "richtek,rt4831-backlight"),
+	MFD_CELL_NAME("rt4831-regulator")
+};
+
+static bool rt4831_is_accessible_reg(struct device *dev, unsigned int reg)
+{
+	if (reg >= RT4831_REG_REVISION && reg <= RT4831_REG_I2CPROT)
+		return true;
+	return false;
+}
+
+static const struct regmap_config rt4831_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = RT4831_REG_I2CPROT,
+
+	.readable_reg = rt4831_is_accessible_reg,
+	.writeable_reg = rt4831_is_accessible_reg,
+};
+
+static int rt4831_probe(struct i2c_client *client)
+{
+	struct gpio_desc *enable_gpio;
+	struct regmap *regmap;
+	unsigned int chip_id;
+	int ret;
+
+	enable_gpio = devm_gpiod_get_optional(&client->dev, "enable", GPIOD_OUT_HIGH);
+	if (IS_ERR(enable_gpio)) {
+		dev_err(&client->dev, "Failed to get 'enable' GPIO\n");
+		return PTR_ERR(enable_gpio);
+	}
+
+	regmap = devm_regmap_init_i2c(client, &rt4831_regmap_config);
+	if (IS_ERR(regmap)) {
+		dev_err(&client->dev, "Failed to initialize regmap\n");
+		return PTR_ERR(regmap);
+	}
+
+	ret = regmap_read(regmap, RT4831_REG_REVISION, &chip_id);
+	if (ret) {
+		dev_err(&client->dev, "Failed to get H/W revision\n");
+		return ret;
+	}
+
+	if ((chip_id & RT4831_VID_MASK) != RICHTEK_VENDOR_ID) {
+		dev_err(&client->dev, "Chip vendor ID 0x%02x not matched\n", chip_id);
+		return -ENODEV;
+	}
+
+	/*
+	 * Used to prevent the abnormal shutdown.
+	 * If SCL/SDA both keep low for one second to reset HW.
+	 */
+	ret = regmap_update_bits(regmap, RT4831_REG_I2CPROT, RT4831_I2CSAFETMR_MASK,
+				 RT4831_I2CSAFETMR_MASK);
+	if (ret) {
+		dev_err(&client->dev, "Failed to enable I2C safety timer\n");
+		return ret;
+	}
+
+	return devm_mfd_add_devices(&client->dev, PLATFORM_DEVID_AUTO, rt4831_subdevs,
+				    ARRAY_SIZE(rt4831_subdevs), NULL, 0, NULL);
+}
+
+static void rt4831_remove(struct i2c_client *client)
+{
+	struct regmap *regmap = dev_get_regmap(&client->dev, NULL);
+	int ret;
+
+	/* Disable WLED and DSV outputs */
+	ret = regmap_update_bits(regmap, RT4831_REG_ENABLE, RT4831_RESET_MASK, RT4831_RESET_MASK);
+	if (ret)
+		dev_warn(&client->dev, "Failed to disable outputs (%pe)\n", ERR_PTR(ret));
+}
+
+static const struct of_device_id __maybe_unused rt4831_of_match[] = {
+	{ .compatible = "richtek,rt4831", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, rt4831_of_match);
+
+static struct i2c_driver rt4831_driver = {
+	.driver = {
+		.name = "rt4831",
+		.of_match_table = rt4831_of_match,
+	},
+	.probe = rt4831_probe,
+	.remove = rt4831_remove,
+};
+module_i2c_driver(rt4831_driver);
+
+MODULE_AUTHOR("ChiYuan Huang <cy_huang@richtek.com>");
+MODULE_DESCRIPTION("Richtek RT4831 core driver");
+MODULE_LICENSE("GPL v2");