On Tue, Apr 09, 2024 at 06:30:43PM +0200, Jocelyn Falempe wrote:
> Add a debugfs file, so you can test drm_panic without freezing
> your machine. This is unsafe, and should be enabled only for
> developer or tester.
>
> To display the drm_panic screen on the device 0:
> echo 1 > /sys/kernel/debug/dri/0/drm_panic_plane_0
>
> v9:
> * Create a debugfs file for each plane in the device's debugfs
> directory. This allows to test for each plane of each GPU
> independently.
>
> Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx>
I was pondering whether this guarantees that the debugfs file disappears
before drm_dev_unregister finishes (otherwise we have a bit a problem),
and looks like we're good.
Maybe add a todo that it would be nice to simulate nmi context, not sure
lockdept can help here ...
Anyway Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/Kconfig | 9 ++++++++
> drivers/gpu/drm/drm_panic.c | 43 ++++++++++++++++++++++++++++++++++++-
> 2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index f8a26423369e..959b19a04101 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -127,6 +127,15 @@ config DRM_PANIC_BACKGROUND_COLOR
> depends on DRM_PANIC
> default 0x000000
>
> +config DRM_PANIC_DEBUG
> + bool "Add a debug fs entry to trigger drm_panic"
> + depends on DRM_PANIC && DEBUG_FS
> + help
> + 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.
> + If in doubt, say "N".
> +
> config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
> bool "Enable refcount backtrace history in the DP MST helpers"
> depends on STACKTRACE_SUPPORT
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index e1ec30b6c04a..78fd6d5d7adc 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -495,6 +495,45 @@ static void drm_panic(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason)
> draw_panic_plane(plane);
> }
>
> +
> +/*
> + * DEBUG FS, This is currently unsafe.
> + * Create one file per plane, so it's possible to debug one plane at a time.
> + */
> +#ifdef CONFIG_DRM_PANIC_DEBUG
> +#include <linux/debugfs.h>
> +
> +static ssize_t debugfs_trigger_write(struct file *file, const char __user *user_buf,
> + size_t count, loff_t *ppos)
> +{
> + bool run;
> +
> + if (kstrtobool_from_user(user_buf, count, &run) == 0 && run) {
> + struct drm_plane *plane = file->private_data;
> +
> + draw_panic_plane(plane);
> + }
> + return count;
> +}
> +
> +static const struct file_operations dbg_drm_panic_ops = {
> + .owner = THIS_MODULE,
> + .write = debugfs_trigger_write,
> + .open = simple_open,
> +};
> +
> +static void debugfs_register_plane(struct drm_plane *plane, int index)
> +{
> + char fname[32];
> +
> + snprintf(fname, 32, "drm_panic_plane_%d", index);
> + debugfs_create_file(fname, 0200, plane->dev->debugfs_root,
> + plane, &dbg_drm_panic_ops);
> +}
> +#else
> +static void debugfs_register_plane(struct drm_plane *plane, int index) {}
> +#endif /* CONFIG_DRM_PANIC_DEBUG */
> +
> /**
> * drm_panic_register() - Initialize DRM panic for a device
> * @dev: the drm device on which the panic screen will be displayed.
> @@ -514,8 +553,10 @@ void drm_panic_register(struct drm_device *dev)
> plane->kmsg_panic.max_reason = KMSG_DUMP_PANIC;
> if (kmsg_dump_register(&plane->kmsg_panic))
> drm_warn(dev, "Failed to register panic handler\n");
> - else
> + else {
> + debugfs_register_plane(plane, registered_plane);
> registered_plane++;
> + }
> }
> if (registered_plane)
> drm_info(dev, "Registered %d planes with drm panic\n", registered_plane);
> --
> 2.44.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
