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, 103 insertions, 0 deletions

diff --git a/drivers/hid/hid-picolcd_backlight.c b/drivers/hid/hid-picolcd_backlight.c
new file mode 100644
index 000000000..4b43b6453
--- /dev/null
+++ b/drivers/hid/hid-picolcd_backlight.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/***************************************************************************
+ *   Copyright (C) 2010-2012 by Bruno Prémont <bonbons@linux-vserver.org>  *
+ *                                                                         *
+ *   Based on Logitech G13 driver (v0.4)                                   *
+ *     Copyright (C) 2009 by Rick L. Vinyard, Jr. <rvinyard@cs.nmsu.edu>   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include <linux/hid.h>
+
+#include <linux/backlight.h>
+
+#include "hid-picolcd.h"
+
+static int picolcd_get_brightness(struct backlight_device *bdev)
+{
+	struct picolcd_data *data = bl_get_data(bdev);
+	return data->lcd_brightness;
+}
+
+static int picolcd_set_brightness(struct backlight_device *bdev)
+{
+	struct picolcd_data *data = bl_get_data(bdev);
+	struct hid_report *report = picolcd_out_report(REPORT_BRIGHTNESS, data->hdev);
+	unsigned long flags;
+
+	if (!report || report->maxfield != 1 || report->field[0]->report_count != 1)
+		return -ENODEV;
+
+	data->lcd_brightness = bdev->props.brightness & 0x0ff;
+	data->lcd_power      = bdev->props.power;
+	spin_lock_irqsave(&data->lock, flags);
+	hid_set_field(report->field[0], 0,
+		      data->lcd_power == BACKLIGHT_POWER_ON ? data->lcd_brightness : 0);
+	if (!(data->status & PICOLCD_FAILED))
+		hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
+	spin_unlock_irqrestore(&data->lock, flags);
+	return 0;
+}
+
+static const struct backlight_ops picolcd_blops = {
+	.update_status  = picolcd_set_brightness,
+	.get_brightness = picolcd_get_brightness,
+};
+
+int picolcd_init_backlight(struct picolcd_data *data, struct hid_report *report)
+{
+	struct device *dev = &data->hdev->dev;
+	struct backlight_device *bdev;
+	struct backlight_properties props;
+	if (!report)
+		return -ENODEV;
+	if (report->maxfield != 1 || report->field[0]->report_count != 1 ||
+			report->field[0]->report_size != 8) {
+		dev_err(dev, "unsupported BRIGHTNESS report");
+		return -EINVAL;
+	}
+
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 0xff;
+	bdev = backlight_device_register(dev_name(dev), dev, data,
+			&picolcd_blops, &props);
+	if (IS_ERR(bdev)) {
+		dev_err(dev, "failed to register backlight\n");
+		return PTR_ERR(bdev);
+	}
+	bdev->props.brightness     = 0xff;
+	data->lcd_brightness       = 0xff;
+	data->backlight            = bdev;
+	picolcd_set_brightness(bdev);
+	return 0;
+}
+
+void picolcd_exit_backlight(struct picolcd_data *data)
+{
+	struct backlight_device *bdev = data->backlight;
+
+	data->backlight = NULL;
+	backlight_device_unregister(bdev);
+}
+
+int picolcd_resume_backlight(struct picolcd_data *data)
+{
+	if (!data->backlight)
+		return 0;
+	return picolcd_set_brightness(data->backlight);
+}
+
+#ifdef CONFIG_PM
+void picolcd_suspend_backlight(struct picolcd_data *data)
+{
+	int bl_power = data->lcd_power;
+	if (!data->backlight)
+		return;
+
+	data->backlight->props.power = BACKLIGHT_POWER_OFF;
+	picolcd_set_brightness(data->backlight);
+	data->lcd_power = data->backlight->props.power = bl_power;
+}
+#endif /* CONFIG_PM */
+