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, 96 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-88pm886.c b/drivers/rtc/rtc-88pm886.c
new file mode 100644
index 000000000..71443ae1b
--- /dev/null
+++ b/drivers/rtc/rtc-88pm886.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/limits.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#include <linux/mfd/88pm886.h>
+
+/*
+ * Time is calculated as the sum of a 32-bit read-only advancing counter and a
+ * writeable constant offset stored in the chip's spare registers.
+ */
+
+static int pm886_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	u32 time;
+	u32 buf;
+	int ret;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_SPARE1, &buf, 4);
+	if (ret)
+		return ret;
+	time = buf;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_CNT1, &buf, 4);
+	if (ret)
+		return ret;
+	time += buf;
+
+	rtc_time64_to_tm(time, tm);
+
+	return 0;
+}
+
+static int pm886_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	u32 buf;
+	int ret;
+
+	ret = regmap_bulk_read(regmap, PM886_REG_RTC_CNT1, &buf, 4);
+	if (ret)
+		return ret;
+
+	buf = rtc_tm_to_time64(tm) - buf;
+
+	return regmap_bulk_write(regmap, PM886_REG_RTC_SPARE1, &buf, 4);
+}
+
+static const struct rtc_class_ops pm886_rtc_ops = {
+	.read_time = pm886_rtc_read_time,
+	.set_time = pm886_rtc_set_time,
+};
+
+static int pm886_rtc_probe(struct platform_device *pdev)
+{
+	struct pm886_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct device *dev = &pdev->dev;
+	struct rtc_device *rtc;
+	int ret;
+
+	platform_set_drvdata(pdev, chip->regmap);
+
+	rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(rtc))
+		return dev_err_probe(dev, PTR_ERR(rtc),
+				"Failed to allocate RTC device\n");
+
+	rtc->ops = &pm886_rtc_ops;
+	rtc->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(rtc);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to register RTC device\n");
+
+	return 0;
+}
+
+static const struct platform_device_id pm886_rtc_id_table[] = {
+	{ .name = "88pm886-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, pm886_rtc_id_table);
+
+static struct platform_driver pm886_rtc_driver = {
+	.driver = {
+		.name = "88pm886-rtc",
+	},
+	.probe = pm886_rtc_probe,
+	.id_table = pm886_rtc_id_table,
+};
+module_platform_driver(pm886_rtc_driver);
+
+MODULE_DESCRIPTION("Marvell 88PM886 RTC driver");
+MODULE_AUTHOR("Karel Balej <balejk@matfyz.cz>");
+MODULE_LICENSE("GPL");