Re: [PATCH 3/3] drm/panic: Add a kconfig option to dump kunits results to png

[Jocelyn Falempe <jfalempe@redhat.com>]

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 <jfalempe@redhat.com>
>> ---
>>   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