Commit c9ff2808 authored by Jocelyn Falempe's avatar Jocelyn Falempe
Browse files

drm/panic: Add support to scanout buffer as array of pages 

Some drivers like virtio-gpu, don't map the scanout buffer in the
kernel. Calling vmap() in a panic handler is not safe, and writing an
atomic_vmap() API is more complex than expected [1].
So instead, pass the array of pages of the scanout buffer to the
panic handler, and map only one page at a time to draw the pixels.
This is obviously slow, but acceptable for a panic handler.

[1] https://lore.kernel.org/dri-devel/20250305152555.318159-1-ryasuoka@redhat.com/



Acked-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Acked-by: default avatarSimona Vetter <simona@ffwll.ch>
Signed-off-by: default avatarJocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20250407140138.162383-3-jfalempe@redhat.com
parent 8702048b

drivers/gpu/drm/drm_panic.c

+136 −6
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 
 */



#include <linux/font.h>

#include <linux/highmem.h>

#include <linux/init.h>

#include <linux/iosys-map.h>

#include <linux/kdebug.h>
@@ -154,6 +155,90 @@ static void drm_panic_blit_pixel(struct drm_scanout_buffer *sb, struct drm_rect 
				sb->set_pixel(sb, clip->x1 + x, clip->y1 + y, fg_color);

}



static void drm_panic_write_pixel16(void *vaddr, unsigned int offset, u16 color)

{

	u16 *p = vaddr + offset;



	*p = color;

}



static void drm_panic_write_pixel24(void *vaddr, unsigned int offset, u32 color)

{

	u8 *p = vaddr + offset;



	*p++ = color & 0xff;

	color >>= 8;

	*p++ = color & 0xff;

	color >>= 8;

	*p = color & 0xff;

}



static void drm_panic_write_pixel32(void *vaddr, unsigned int offset, u32 color)

{

	u32 *p = vaddr + offset;



	*p = color;

}



static void drm_panic_write_pixel(void *vaddr, unsigned int offset, u32 color, unsigned int cpp)

{

	switch (cpp) {

	case 2:

		drm_panic_write_pixel16(vaddr, offset, color);

		break;

	case 3:

		drm_panic_write_pixel24(vaddr, offset, color);

		break;

	case 4:

		drm_panic_write_pixel32(vaddr, offset, color);

		break;

	default:

		pr_debug_once("Can't blit with pixel width %d\n", cpp);

	}

}



/*

 * The scanout buffer pages are not mapped, so for each pixel,

 * use kmap_local_page_try_from_panic() to map the page, and write the pixel.

 * Try to keep the map from the previous pixel, to avoid too much map/unmap.

 */

static void drm_panic_blit_page(struct page **pages, unsigned int dpitch,

				unsigned int cpp, const u8 *sbuf8,

				unsigned int spitch, struct drm_rect *clip,

				unsigned int scale, u32 fg32)

{

	unsigned int y, x;

	unsigned int page = ~0;

	unsigned int height = drm_rect_height(clip);

	unsigned int width = drm_rect_width(clip);

	void *vaddr = NULL;



	for (y = 0; y < height; y++) {

		for (x = 0; x < width; x++) {

			if (drm_draw_is_pixel_fg(sbuf8, spitch, x / scale, y / scale)) {

				unsigned int new_page;

				unsigned int offset;



				offset = (y + clip->y1) * dpitch + (x + clip->x1) * cpp;

				new_page = offset >> PAGE_SHIFT;

				offset = offset % PAGE_SIZE;

				if (new_page != page) {

					if (!pages[new_page])

						continue;

					if (vaddr)

						kunmap_local(vaddr);

					page = new_page;

					vaddr = kmap_local_page_try_from_panic(pages[page]);

				}

				if (vaddr)

					drm_panic_write_pixel(vaddr, offset, fg32, cpp);

			}

		}

	}

	if (vaddr)

		kunmap_local(vaddr);

}



/*

 * drm_panic_blit - convert a monochrome image to a linear framebuffer

 * @sb: destination scanout buffer
@@ -177,6 +262,10 @@ static void drm_panic_blit(struct drm_scanout_buffer *sb, struct drm_rect *clip, 
	if (sb->set_pixel)

		return drm_panic_blit_pixel(sb, clip, sbuf8, spitch, scale, fg_color);



	if (sb->pages)

		return drm_panic_blit_page(sb->pages, sb->pitch[0], sb->format->cpp[0],

					   sbuf8, spitch, clip, scale, fg_color);



	map = sb->map[0];

	iosys_map_incr(&map, clip->y1 * sb->pitch[0] + clip->x1 * sb->format->cpp[0]);
@@ -209,6 +298,35 @@ static void drm_panic_fill_pixel(struct drm_scanout_buffer *sb, 
			sb->set_pixel(sb, clip->x1 + x, clip->y1 + y, color);

}



static void drm_panic_fill_page(struct page **pages, unsigned int dpitch,

				unsigned int cpp, struct drm_rect *clip,

				u32 color)

{

	unsigned int y, x;

	unsigned int page = ~0;

	void *vaddr = NULL;



	for (y = clip->y1; y < clip->y2; y++) {

		for (x = clip->x1; x < clip->x2; x++) {

			unsigned int new_page;

			unsigned int offset;



			offset = y * dpitch + x * cpp;

			new_page = offset >> PAGE_SHIFT;

			offset = offset % PAGE_SIZE;

			if (new_page != page) {

				if (vaddr)

					kunmap_local(vaddr);

				page = new_page;

				vaddr = kmap_local_page_try_from_panic(pages[page]);

			}

			drm_panic_write_pixel(vaddr, offset, color, cpp);

		}

	}

	if (vaddr)

		kunmap_local(vaddr);

}



/*

 * drm_panic_fill - Fill a rectangle with a color

 * @sb: destination scanout buffer
@@ -225,6 +343,10 @@ static void drm_panic_fill(struct drm_scanout_buffer *sb, struct drm_rect *clip, 
	if (sb->set_pixel)

		return drm_panic_fill_pixel(sb, clip, color);



	if (sb->pages)

		return drm_panic_fill_page(sb->pages, sb->pitch[0], sb->format->cpp[0],

					   clip, color);



	map = sb->map[0];

	iosys_map_incr(&map, clip->y1 * sb->pitch[0] + clip->x1 * sb->format->cpp[0]);
@@ -709,16 +831,24 @@ static void draw_panic_plane(struct drm_plane *plane, const char *description) 
	if (!drm_panic_trylock(plane->dev, flags))

		return;



	drm_panic_set_description(description);



	ret = plane->helper_private->get_scanout_buffer(plane, &sb);



	if (!ret && drm_panic_is_format_supported(sb.format)) {

	if (ret || !drm_panic_is_format_supported(sb.format))

		goto unlock;



	/* One of these should be set, or it can't draw pixels */

	if (!sb.set_pixel && !sb.pages && iosys_map_is_null(&sb.map[0]))

		goto unlock;



	drm_panic_set_description(description);



	draw_panic_dispatch(&sb);

	if (plane->helper_private->panic_flush)

		plane->helper_private->panic_flush(plane);

	}



	drm_panic_clear_description();



unlock:

	drm_panic_unlock(plane->dev, flags);

}

include/drm/drm_panic.h

+11 −1
Original line number Diff line number Diff line
@@ -39,6 +39,16 @@ struct drm_scanout_buffer { 
	 */

	struct iosys_map map[DRM_FORMAT_MAX_PLANES];



	/**

	 * @pages: Optional, if the scanout buffer is not mapped, set this field

	 * to the array of pages of the scanout buffer. The panic code will use

	 * kmap_local_page_try_from_panic() to map one page at a time to write

	 * all the pixels. This array shouldn't be allocated from the

	 * get_scanoutbuffer() callback.

	 * The scanout buffer should be in linear format.

	 */

	struct page **pages;



	/**

	 * @width: Width of the scanout buffer, in pixels.

	 */
@@ -57,7 +67,7 @@ struct drm_scanout_buffer { 
	/**

	 * @set_pixel: Optional function, to set a pixel color on the

	 * framebuffer. It allows to handle special tiling format inside the

	 * driver.

	 * driver. It takes precedence over the @map and @pages fields.

	 */

	void (*set_pixel)(struct drm_scanout_buffer *sb, unsigned int x,

			  unsigned int y, u32 color);