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, 88 insertions, 0 deletions

diff --git a/drivers/hid/hid-picolcd_lcd.c b/drivers/hid/hid-picolcd_lcd.c
new file mode 100644
index 000000000..318f19eac
--- /dev/null
+++ b/drivers/hid/hid-picolcd_lcd.c
@@ -0,0 +1,88 @@
+// 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/fb.h>
+#include <linux/lcd.h>
+
+#include "hid-picolcd.h"
+
+/*
+ * lcd class device
+ */
+static int picolcd_get_contrast(struct lcd_device *ldev)
+{
+	struct picolcd_data *data = lcd_get_data(ldev);
+	return data->lcd_contrast;
+}
+
+static int picolcd_set_contrast(struct lcd_device *ldev, int contrast)
+{
+	struct picolcd_data *data = lcd_get_data(ldev);
+	struct hid_report *report = picolcd_out_report(REPORT_CONTRAST, data->hdev);
+	unsigned long flags;
+
+	if (!report || report->maxfield != 1 || report->field[0]->report_count != 1)
+		return -ENODEV;
+
+	data->lcd_contrast = contrast & 0x0ff;
+	spin_lock_irqsave(&data->lock, flags);
+	hid_set_field(report->field[0], 0, data->lcd_contrast);
+	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 lcd_ops picolcd_lcdops = {
+	.get_contrast   = picolcd_get_contrast,
+	.set_contrast   = picolcd_set_contrast,
+};
+
+int picolcd_init_lcd(struct picolcd_data *data, struct hid_report *report)
+{
+	struct device *dev = &data->hdev->dev;
+	struct lcd_device *ldev;
+
+	if (!report)
+		return -ENODEV;
+	if (report->maxfield != 1 || report->field[0]->report_count != 1 ||
+			report->field[0]->report_size != 8) {
+		dev_err(dev, "unsupported CONTRAST report");
+		return -EINVAL;
+	}
+
+	ldev = lcd_device_register(dev_name(dev), dev, data, &picolcd_lcdops);
+	if (IS_ERR(ldev)) {
+		dev_err(dev, "failed to register LCD\n");
+		return PTR_ERR(ldev);
+	}
+	ldev->props.max_contrast = 0x0ff;
+	data->lcd_contrast = 0xe5;
+	data->lcd = ldev;
+	picolcd_set_contrast(ldev, 0xe5);
+	return 0;
+}
+
+void picolcd_exit_lcd(struct picolcd_data *data)
+{
+	struct lcd_device *ldev = data->lcd;
+
+	data->lcd = NULL;
+	lcd_device_unregister(ldev);
+}
+
+int picolcd_resume_lcd(struct picolcd_data *data)
+{
+	if (!data->lcd)
+		return 0;
+	return picolcd_set_contrast(data->lcd, data->lcd_contrast);
+}
+