Re: [PATCH 04/12] drm/panic: Return errno codes if panic output fails

[Jocelyn Falempe <jfalempe@redhat.com>]

On 18/08/2026 14:28, Thomas Zimmermann wrote:
> Return errno codes from the panic output helpers to detect invalid
> panic handling. Avoid flushing the display if an error ocured. The
> unflushed display output might be helpful in debugging.
> 
> For now, test the result values in the panic test cases. A later patch
> will add support for retrying failed panic output.

Thanks, it looks good to me.

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>   drivers/gpu/drm/drm_panic.c            | 41 +++++++++++++++++---------
>   drivers/gpu/drm/tests/drm_panic_test.c | 16 ++++++----
>   2 files changed, 37 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index 96d238bfceee..594235661710 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -478,7 +478,7 @@ static void drm_panic_logo_draw(struct drm_scanout_buffer *sb, struct drm_rect *
>   				   fg_color);
>   }
>   
> -static void draw_panic_screen_user(struct drm_scanout_buffer *sb)
> +static int draw_panic_screen_user(struct drm_scanout_buffer *sb)
>   {
>   	u32 fg_color = drm_draw_color_from_xrgb8888(CONFIG_DRM_PANIC_FOREGROUND_COLOR,
>   						    sb->format->format);
> @@ -489,7 +489,7 @@ static void draw_panic_screen_user(struct drm_scanout_buffer *sb)
>   	unsigned int msg_width, msg_height;
>   
>   	if (!font)
> -		return;
> +		return -EINVAL;
>   
>   	r_screen = DRM_RECT_INIT(0, 0, sb->width, sb->height);
>   	drm_panic_logo_rect(&r_logo, font);
> @@ -508,6 +508,8 @@ static void draw_panic_screen_user(struct drm_scanout_buffer *sb)
>   		drm_panic_logo_draw(sb, &r_logo, font, fg_color);
>   
>   	draw_txt_rectangle(sb, font, panic_msg, panic_msg_lines, true, &r_msg, fg_color);
> +
> +	return 0;
>   }
>   
>   /*
> @@ -547,7 +549,7 @@ static int draw_line_with_wrap(struct drm_scanout_buffer *sb, const struct font_
>    * Draw the kmsg buffer to the screen, starting from the youngest message at the bottom,
>    * and going up until reaching the top of the screen.
>    */
> -static void draw_panic_screen_kmsg(struct drm_scanout_buffer *sb)
> +static int draw_panic_screen_kmsg(struct drm_scanout_buffer *sb)
>   {
>   	u32 fg_color = drm_draw_color_from_xrgb8888(CONFIG_DRM_PANIC_FOREGROUND_COLOR,
>   						    sb->format->format);
> @@ -562,7 +564,7 @@ static void draw_panic_screen_kmsg(struct drm_scanout_buffer *sb)
>   	int yoffset;
>   
>   	if (!font || font->width > sb->width)
> -		return;
> +		return -EINVAL;
>   
>   	yoffset = sb->height - font->height - (sb->height % font->height) / 2;
>   
> @@ -589,6 +591,8 @@ static void draw_panic_screen_kmsg(struct drm_scanout_buffer *sb)
>   			start--;
>   		}
>   	}
> +
> +	return 0;
>   }
>   
>   #if defined(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> @@ -814,10 +818,11 @@ static int _draw_panic_screen_qr_code(struct drm_scanout_buffer *sb)
>   	return 0;
>   }
>   
> -static void draw_panic_screen_qr_code(struct drm_scanout_buffer *sb)
> +static int draw_panic_screen_qr_code(struct drm_scanout_buffer *sb)
>   {
>   	if (_draw_panic_screen_qr_code(sb))
>   		draw_panic_screen_user(sb);
> +	return 0;
>   }
>   #else
>   static void drm_panic_qr_init(void) {};
> @@ -888,23 +893,25 @@ static bool drm_panic_is_format_supported(const struct drm_format_info *format)
>   	return drm_draw_can_convert_from_xrgb8888(format->format);
>   }
>   
> -static void draw_panic_dispatch(struct drm_scanout_buffer *sb)
> +static int draw_panic_dispatch(struct drm_scanout_buffer *sb)
>   {
> +	int ret;
> +
>   	switch (drm_panic_type) {
>   	case DRM_PANIC_TYPE_KMSG:
> -		draw_panic_screen_kmsg(sb);
> +		ret = draw_panic_screen_kmsg(sb);
>   		break;
> -
>   #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
>   	case DRM_PANIC_TYPE_QR:
> -		draw_panic_screen_qr_code(sb);
> +		ret = draw_panic_screen_qr_code(sb);
>   		break;
>   #endif
> -
>   	case DRM_PANIC_TYPE_USER:
>   	default:
> -		draw_panic_screen_user(sb);
> +		ret = draw_panic_screen_user(sb);
>   	}
> +
> +	return ret;
>   }
>   
>   static void drm_panic_set_description(const char *description)
> @@ -951,9 +958,15 @@ static void draw_panic_plane(struct drm_plane *plane, const char *description)
>   
>   	drm_panic_set_description(description);
>   
> -	draw_panic_dispatch(&sb);
> -	if (plane->helper_private->panic_flush)
> -		plane->helper_private->panic_flush(plane);
> +	ret = draw_panic_dispatch(&sb);
> +	if (!ret) {
> +		/*
> +		 * Only flush if we have a panic screen to display. Otherwise
> +		 * it's probably better to leave the display output as-is.
> +		 */
> +		if (plane->helper_private->panic_flush)
> +			plane->helper_private->panic_flush(plane);
> +	}
>   
>   	drm_panic_clear_description();
>   
> diff --git a/drivers/gpu/drm/tests/drm_panic_test.c b/drivers/gpu/drm/tests/drm_panic_test.c
> index ad2f3a2f93b6..fdd77b0cc54c 100644
> --- a/drivers/gpu/drm/tests/drm_panic_test.c
> +++ b/drivers/gpu/drm/tests/drm_panic_test.c
> @@ -30,7 +30,7 @@ struct drm_test_mode {
>   	const int width;
>   	const int height;
>   	const u32 format;
> -	void (*draw_screen)(struct drm_scanout_buffer *sb);
> +	int (*draw_screen)(struct drm_scanout_buffer *sb);
>   	const char *fname;
>   };
>   
> @@ -87,7 +87,7 @@ static void drm_test_panic_screen_user_map(struct kunit *test)
>   	const struct drm_test_mode *params = test->param_value;
>   	char *fb;
>   	int fb_size;
> -	int i;
> +	int i, ret;
>   
>   	sb->format = drm_format_info(params->format);
>   	fb_size = params->width * params->height * sb->format->cpp[0];
> @@ -102,7 +102,8 @@ static void drm_test_panic_screen_user_map(struct kunit *test)
>   	sb->height = params->height;
>   	sb->pitch[0] = params->width * sb->format->cpp[0];
>   
> -	params->draw_screen(sb);
> +	ret = params->draw_screen(sb);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
>   
>   	for (i = 0; i < fb_size; i++)
>   		drm_panic_check_color_byte(test, fb[i]);
> @@ -119,7 +120,7 @@ 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;
> +	int fb_size, p, i, npages, ret;
>   	struct page **pages;
>   	u8 *vaddr;
>   
> @@ -146,7 +147,8 @@ static void drm_test_panic_screen_user_page(struct kunit *test)
>   	sb->height = params->height;
>   	sb->pitch[0] = params->width * sb->format->cpp[0];
>   
> -	params->draw_screen(sb);
> +	ret = params->draw_screen(sb);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
>   
>   	for (p = 0; p < npages; p++) {
>   		int bytes_in_page = (p == npages - 1) ? fb_size - p * PAGE_SIZE : PAGE_SIZE;
> @@ -182,6 +184,7 @@ 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;
> +	int ret;
>   
>   	sb->format = drm_format_info(params->format);
>   	sb->set_pixel = drm_test_panic_set_pixel;
> @@ -189,7 +192,8 @@ static void drm_test_panic_screen_user_set_pixel(struct kunit *test)
>   	sb->height = params->height;
>   	sb->private = test;
>   
> -	params->draw_screen(sb);
> +	ret = params->draw_screen(sb);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
>   }
>   
>   static void drm_test_panic_desc(const struct drm_test_mode *t, char *desc)