On 27/08/2025 11:52, Maxime Ripard wrote:
Hi,

On Thu, Aug 21, 2025 at 11:49:07AM +0200, Jocelyn Falempe wrote:
This is a bit hacky, but very handy if you want to customize the
panic screen.
It allows to dump the generated images to the logs, and then a python
script can convert it to .png files. It makes it easy to check how
the panic screen will look on different resolutions, without having
to crash a VM.
To not pollute the logs, it uses a monochrome framebuffer, compress
it with zlib, and base64 encode it.

Signed-off-by: Jocelyn Falempe <[email protected]>
---
  drivers/gpu/drm/Kconfig.debug          |  14 ++++
  drivers/gpu/drm/tests/drm_panic_test.c | 111 +++++++++++++++++++++++++
  scripts/kunitpanic2png.py              |  53 ++++++++++++
  3 files changed, 178 insertions(+)
  create mode 100755 scripts/kunitpanic2png.py

diff --git a/drivers/gpu/drm/Kconfig.debug b/drivers/gpu/drm/Kconfig.debug
index 05dc43c0b8c5..d8ae85132d32 100644
--- a/drivers/gpu/drm/Kconfig.debug
+++ b/drivers/gpu/drm/Kconfig.debug
@@ -84,6 +84,20 @@ config DRM_KUNIT_TEST
If in doubt, say "N". +config DRM_PANIC_KUNIT_TEST_DUMP
+       bool "Enable screen dump to logs in KUnit tests for drm_panic"
+       default n
+       depends on DRM && DRM_PANIC && DRM_KUNIT_TEST
+       select ZLIB_DEFLATE
+       help
+         This allows to dump the panic screen to the KUnit tests logs.
+         It's possible with a small python script to write pngs from the logs.
+
+         This is only to help developers customizing the drm_panic screen,
+         checking the result for different resolutions.
+
+         If in doubt, say "N"
+
  config DRM_TTM_KUNIT_TEST
        tristate "KUnit tests for TTM" if !KUNIT_ALL_TESTS
        default n
diff --git a/drivers/gpu/drm/tests/drm_panic_test.c 
b/drivers/gpu/drm/tests/drm_panic_test.c
index 46ff3e5e0e5d..8cddb845aea9 100644
--- a/drivers/gpu/drm/tests/drm_panic_test.c
+++ b/drivers/gpu/drm/tests/drm_panic_test.c
@@ -115,24 +115,135 @@ static void drm_test_panic_screen_user_page(struct kunit 
*test)
        kfree(pages);
  }
+#ifdef CONFIG_DRM_PANIC_KUNIT_TEST_DUMP
+#include <linux/base64.h>
+#include <linux/delay.h>
+#include <linux/zlib.h>
+
+#define LINE_LEN 128
+
+#define COMPR_LEVEL 6
+#define WINDOW_BITS 12
+#define MEM_LEVEL 4
+
+static int compress_image(u8 *src, int size, u8 *dst)
+{
+       struct z_stream_s stream;
+
+       stream.workspace = kmalloc(zlib_deflate_workspacesize(WINDOW_BITS, 
MEM_LEVEL),
+                                  GFP_KERNEL);
+
+       if (zlib_deflateInit2(&stream, COMPR_LEVEL, Z_DEFLATED, WINDOW_BITS,
+                             MEM_LEVEL, Z_DEFAULT_STRATEGY) != Z_OK)
+               return -EINVAL;
+
+       stream.next_in = src;
+       stream.avail_in = size;
+       stream.total_in = 0;
+       stream.next_out = dst;
+       stream.avail_out = size;
+       stream.total_out = 0;
+
+       if (zlib_deflate(&stream, Z_FINISH) != Z_STREAM_END)
+               return -EINVAL;
+
+       if (zlib_deflateEnd(&stream) != Z_OK)
+               return -EINVAL;
+
+       kfree(stream.workspace);
+
+       return stream.total_out;
+}
+
+static void dump_image(u8 *fb, unsigned int width, unsigned int height)
+{
+       int len = 0;
+       char *dst;
+       char *compressed;
+       int sent = 0;
+       int stride = DIV_ROUND_UP(width, 8);
+       int size = stride * height;
+
+       compressed = vzalloc(size);
+       if (!compressed)
+               return;
+       len = compress_image(fb, size, compressed);
+       if (len < 0) {
+               pr_err("Compression failed %d", len);
+               return;
+       }
+
+       dst = vzalloc(4 * DIV_ROUND_UP(len, 3) + 1);
+       if (!dst)
+               return;
+
+       len = base64_encode(compressed, len, dst);
+
+       pr_info("KUNIT PANIC IMAGE DUMP START %dx%d", width, height);
+       while (len > 0) {
+               char save = dst[sent + LINE_LEN];
+
+               dst[sent + LINE_LEN] = 0;
+               pr_info("%s", dst + sent);
+               dst[sent + LINE_LEN] = save;
+               sent += LINE_LEN;
+               len -= LINE_LEN;
+       }
+       pr_info("KUNIT PANIC IMAGE DUMP END");

The kunit test output format is defined, and we should probably use a
diagnostic line for this:
https://docs.kernel.org/dev-tools/ktap.html#diagnostic-lines

We should probably cc the kunit maintainers about this too.

Thanks for the pointer, I will also experiment with debugfs, as suggested by Thomas.

Best regards,

--

Jocelyn




Maxime

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