On 10/09/2025 12:49, Maxime Ripard wrote:
Hi,
On Mon, Sep 08, 2025 at 11:00:31AM +0200, Jocelyn Falempe wrote:
This adds a new drm_panic/draw_test file in debugfs.
This file allows to test the panic screen rendering at different
resolution and pixel format.
It's useful only for kernel developers that want to create or
customize a panic screen.
If you want to check the result at 1024x768 using XRGB8888:
cd /sys/kernel/debug/drm_panic/
exec 3<> draw_test
echo 1024x768:XR24 >&3
cat <&3 > ~/panic_screen.raw
exec 3<&-
Signed-off-by: Jocelyn Falempe <jfale...@redhat.com>
I see what you meant in your previous version, and I misunderstood what
you were saying, sorry.
v2:
* Use debugfs instead of sending the framebuffer through the kunit logs.
(Thomas Zimmermann).
drivers/gpu/drm/Kconfig | 2 +
drivers/gpu/drm/drm_panic.c | 117 ++++++++++++++++++++++++++++++++++++
2 files changed, 119 insertions(+)
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index f7ea8e895c0c..0d3146070d9c 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -83,6 +83,8 @@ config DRM_PANIC_DEBUG
Add dri/[device]/drm_panic_plane_x in the kernel debugfs, to force the
panic handler to write the panic message to this plane scanout buffer.
This is unsafe and should not be enabled on a production build.
+ Also adds a drm_panic/draw_test file in debugfs, to easily test the
+ panic screen rendering.
If in doubt, say "N".
config DRM_PANIC_SCREEN
diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index d89812ff1935..0c01d6067eab 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -873,6 +873,7 @@ static void drm_panic(struct kmsg_dumper *dumper, struct
kmsg_dump_detail *detai
*/
#ifdef CONFIG_DRM_PANIC_DEBUG
#include <linux/debugfs.h>
+#include <linux/vmalloc.h>
static ssize_t debugfs_trigger_write(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
@@ -901,8 +902,122 @@ static void debugfs_register_plane(struct drm_plane
*plane, int index)
debugfs_create_file(fname, 0200, plane->dev->debugfs_root,
plane, &dbg_drm_panic_ops);
}
+
+/*
+ * Draw test interface
+ * This can be used to check the panic screen at any resolution/pixel format.
+ * The framebuffer memory is freed when the file is closed, so use this sh
+ * script to write the parameters and read the result without closing the file.
+ * cd /sys/kernel/debug/drm_panic/
+ * exec 3<> draw_test
+ * echo 1024x768:XR24 >&3
+ * cat <&3 > ~/panic_screen.raw
+ * exec 3<&-
+ */
This should be documented properly, and I'm also kind of wondering how
that would fit in the larger testing ecosystem.
Ie, how can someone that just starts contributing to Linux, or is
setting up a CI platform, can have that test running.
kunit is great for that, kselftests to some extent too, but I'm not sure
an ad-hoc interface is.
It's a bit harder to setup, but also allows to do some useful things.
I've written a small GUI application which displays the contents of the
debugfs drm_panic/draw_test file in a window.
The displayed content is automatically refreshed whenever the window is
resized, making it easy to inspect the DRM panic output at any screen
resolution.
https://gitlab.com/kdj0c/panicviewer
Unless we create IGT tests for it too maybe?
Yes, I should also take a look at what IGT can do.
Maxime
--
Jocelyn
