[PATCH 5/5] drm/panic: Add panic description

[Jocelyn Falempe]

Now that kmsg dump callback has the description parameter, use it in
the user panic screen.
This is the string passed to panic(), like "VFS: Unable to mount root
fs on xxx" or "Attempted to kill init! exitcode=0xxxx".
It gives a hint on why the panic occurred, without being too cryptic.

Signed-off-by: Jocelyn Falempe <jfale...@redhat.com>
---
 drivers/gpu/drm/drm_panic.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index 2efede7fa23a..fb283695f50e 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -81,6 +81,8 @@ static struct drm_panic_line panic_msg[] = {
        PANIC_LINE("KERNEL PANIC!"),
        PANIC_LINE(""),
        PANIC_LINE("Please reboot your computer."),
+       PANIC_LINE(""),
+       PANIC_LINE(""), /* will be replaced by the panic description */
 };
 
 static const struct drm_panic_line logo_ascii[] = {
@@ -633,7 +635,20 @@ static void draw_panic_dispatch(struct drm_scanout_buffer 
*sb)
        }
 }
 
-static void draw_panic_plane(struct drm_plane *plane)
+static void drm_panic_set_description(const char *description)
+{
+       u32 len;
+       if (description) {
+               panic_msg[4].txt = description;
+               len = strlen(description);
+               /* ignore the last newline character */
+               if (len && description[len - 1] == '\n')
+                       len -= 1;
+               panic_msg[4].len = len;
+       }
+}
+
+static void draw_panic_plane(struct drm_plane *plane, const char *description)
 {
        struct drm_scanout_buffer sb = { };
        int ret;
@@ -642,6 +657,8 @@ static void draw_panic_plane(struct drm_plane *plane)
        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)) {
@@ -662,7 +679,7 @@ static void drm_panic(struct kmsg_dumper *dumper, struct 
kmsg_dump_detail *detai
        struct drm_plane *plane = to_drm_plane(dumper);
 
        if (detail->reason == KMSG_DUMP_PANIC)
-               draw_panic_plane(plane);
+               draw_panic_plane(plane, detail->description);
 }
 
 
@@ -682,7 +699,7 @@ static ssize_t debugfs_trigger_write(struct file *file, 
const char __user *user_
        if (kstrtobool_from_user(user_buf, count, &run) == 0 && run) {
                struct drm_plane *plane = file->private_data;
 
-               draw_panic_plane(plane);
+               draw_panic_plane(plane, "Test from debugfs");
        }
        return count;
 }
-- 
2.45.2