drm/panic: Add kunit tests for drm_panic

Add kunit tests for drm_panic.
They check that drawing the panic screen doesn't crash, but they
don't check the correctness of the resulting image.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patch.msgid.link/20251216082524.115980-3-jfalempe@redhat.com
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>

MAINTAINERS

@@ -8749,6 +8749,7 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	drivers/gpu/drm/drm_draw.c
 F:	drivers/gpu/drm/drm_draw_internal.h
 F:	drivers/gpu/drm/drm_panic*.c
+F:	drivers/gpu/drm/tests/drm_panic_test.c
 F:	include/drm/drm_panic*
 
 DRM PANIC QR CODE

drivers/gpu/drm/drm_panic.c

@@ -1084,3 +1084,7 @@ void drm_panic_exit(void)
 {
 	drm_panic_qr_exit();
 }
+
+#ifdef CONFIG_DRM_KUNIT_TEST
+#include "tests/drm_panic_test.c"
+#endif

drivers/gpu/drm/tests/drm_panic_test.c

@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0 or MIT
+/*
+ * Copyright (c) 2025 Red Hat.
+ * Author: Jocelyn Falempe <jfalempe@redhat.com>
+ *
+ * KUNIT tests for drm panic
+ */
+
+#include <drm/drm_fourcc.h>
+#include <drm/drm_panic.h>
+
+#include <kunit/test.h>
+
+#include <linux/units.h>
+#include <linux/vmalloc.h>
+
+/* Check the framebuffer color only if the panic colors are the default */
+#if (CONFIG_DRM_PANIC_BACKGROUND_COLOR == 0 && \
+	CONFIG_DRM_PANIC_FOREGROUND_COLOR == 0xffffff)
+
+static void drm_panic_check_color_byte(struct kunit *test, u8 b)
+{
+	KUNIT_EXPECT_TRUE(test, (b == 0 || b == 0xff));
+}
+#else
+static void drm_panic_check_color_byte(struct kunit *test, u8 b) {}
+#endif
+
+struct drm_test_mode {
+	const int width;
+	const int height;
+	const u32 format;
+	void (*draw_screen)(struct drm_scanout_buffer *sb);
+	const char *fname;
+};
+
+/*
+ * Run all tests for the 3 panic screens: user, kmsg and qr_code
+ */
+#define DRM_TEST_MODE_LIST(func) \
+	DRM_PANIC_TEST_MODE(1024, 768, DRM_FORMAT_XRGB8888, func) \
+	DRM_PANIC_TEST_MODE(300, 200, DRM_FORMAT_XRGB8888, func) \
+	DRM_PANIC_TEST_MODE(1920, 1080, DRM_FORMAT_XRGB8888, func) \
+	DRM_PANIC_TEST_MODE(1024, 768, DRM_FORMAT_RGB565, func) \
+	DRM_PANIC_TEST_MODE(1024, 768, DRM_FORMAT_RGB888, func) \
+
+#define DRM_PANIC_TEST_MODE(w, h, f, name) { \
+	.width = w, \
+	.height = h, \
+	.format = f, \
+	.draw_screen = draw_panic_screen_##name, \
+	.fname = #name, \
+	}, \
+
+static const struct drm_test_mode drm_test_modes_cases[] = {
+	DRM_TEST_MODE_LIST(user)
+	DRM_TEST_MODE_LIST(kmsg)
+#if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
+	DRM_TEST_MODE_LIST(qr_code)
+#endif
+};
+
+#undef DRM_PANIC_TEST_MODE
+
+static int drm_test_panic_init(struct kunit *test)
+{
+	struct drm_scanout_buffer *priv;
+
+	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, priv);
+
+	test->priv = priv;
+
+	drm_panic_set_description("Kunit testing");
+
+	return 0;
+}
+
+/*
+ * Test drawing the panic screen, using a memory mapped framebuffer
+ * Set the whole buffer to 0xa5, and then check that all pixels have been
+ * written.
+ */
+static void drm_test_panic_screen_user_map(struct kunit *test)
+{
+	struct drm_scanout_buffer *sb = test->priv;
+	const struct drm_test_mode *params = test->param_value;
+	char *fb;
+	int fb_size;
+	int i;
+
+	sb->format = drm_format_info(params->format);
+	fb_size = params->width * params->height * sb->format->cpp[0];
+
+	fb = vmalloc(fb_size);
+	KUNIT_ASSERT_NOT_NULL(test, fb);
+
+	memset(fb, 0xa5, fb_size);
+
+	iosys_map_set_vaddr(&sb->map[0], fb);
+	sb->width = params->width;
+	sb->height = params->height;
+	sb->pitch[0] = params->width * sb->format->cpp[0];
+
+	params->draw_screen(sb);
+
+	for (i = 0; i < fb_size; i++)
+		drm_panic_check_color_byte(test, fb[i]);
+
+	vfree(fb);
+}
+
+/*
+ * Test drawing the panic screen, using a list of pages framebuffer
+ * Set the whole buffer to 0xa5, and then check that all pixels have been
+ * written.
+ */
+static void drm_test_panic_screen_user_page(struct kunit *test)
+{
+	struct drm_scanout_buffer *sb = test->priv;
+	const struct drm_test_mode *params = test->param_value;
+	int fb_size, p, i, npages;
+	struct page **pages;
+	u8 *vaddr;
+
+	sb->format = drm_format_info(params->format);
+	fb_size = params->width * params->height * sb->format->cpp[0];
+	npages = DIV_ROUND_UP(fb_size, PAGE_SIZE);
+
+	pages = kmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, pages);
+
+	for (p = 0; p < npages; p++) {
+		pages[p] = alloc_page(GFP_KERNEL);
+		if (!pages[p]) {
+			npages = p - 1;
+			KUNIT_FAIL(test, "Can't allocate page\n");
+			goto free_pages;
+		}
+		vaddr = kmap_local_page(pages[p]);
+		memset(vaddr, 0xa5, PAGE_SIZE);
+		kunmap_local(vaddr);
+	}
+	sb->pages = pages;
+	sb->width = params->width;
+	sb->height = params->height;
+	sb->pitch[0] = params->width * sb->format->cpp[0];
+
+	params->draw_screen(sb);
+
+	for (p = 0; p < npages; p++) {
+		int bytes_in_page = (p == npages - 1) ? fb_size - p * PAGE_SIZE : PAGE_SIZE;
+
+		vaddr = kmap_local_page(pages[p]);
+		for (i = 0; i < bytes_in_page; i++)
+			drm_panic_check_color_byte(test, vaddr[i]);
+
+		kunmap_local(vaddr);
+	}
+
+free_pages:
+	for (p = 0; p < npages; p++)
+		__free_page(pages[p]);
+	kfree(pages);
+}
+
+static void drm_test_panic_set_pixel(struct drm_scanout_buffer *sb,
+				     unsigned int x,
+				     unsigned int y,
+				     u32 color)
+{
+	struct kunit *test = (struct kunit *)sb->private;
+
+	KUNIT_ASSERT_TRUE(test, x < sb->width && y < sb->height);
+}
+
+/*
+ * Test drawing the panic screen, using the set_pixel callback
+ * Check that all calls to set_pixel() are within the framebuffer
+ */
+static void drm_test_panic_screen_user_set_pixel(struct kunit *test)
+{
+	struct drm_scanout_buffer *sb = test->priv;
+	const struct drm_test_mode *params = test->param_value;
+
+	sb->format = drm_format_info(params->format);
+	sb->set_pixel = drm_test_panic_set_pixel;
+	sb->width = params->width;
+	sb->height = params->height;
+	sb->private = test;
+
+	params->draw_screen(sb);
+}
+
+static void drm_test_panic_desc(const struct drm_test_mode *t, char *desc)
+{
+	sprintf(desc, "Panic screen %s, mode: %d x %d \t%p4cc",
+		t->fname, t->width, t->height, &t->format);
+}
+
+KUNIT_ARRAY_PARAM(drm_test_panic_screen_user_map, drm_test_modes_cases, drm_test_panic_desc);
+KUNIT_ARRAY_PARAM(drm_test_panic_screen_user_page, drm_test_modes_cases, drm_test_panic_desc);
+KUNIT_ARRAY_PARAM(drm_test_panic_screen_user_set_pixel, drm_test_modes_cases, drm_test_panic_desc);
+
+static struct kunit_case drm_panic_screen_user_test[] = {
+	KUNIT_CASE_PARAM(drm_test_panic_screen_user_map,
+			 drm_test_panic_screen_user_map_gen_params),
+	KUNIT_CASE_PARAM(drm_test_panic_screen_user_page,
+			 drm_test_panic_screen_user_page_gen_params),
+	KUNIT_CASE_PARAM(drm_test_panic_screen_user_set_pixel,
+			 drm_test_panic_screen_user_set_pixel_gen_params),
+	{ }
+};
+
+static struct kunit_suite drm_panic_suite = {
+	.name = "drm_panic",
+	.init = drm_test_panic_init,
+	.test_cases = drm_panic_screen_user_test,
+};
+
+kunit_test_suite(drm_panic_suite);