Re: [PATCH v4 2/4] drm/panic: Add a drm panic handler

["Noralf Trønnes" <noralf@tronnes.org>]

On 10/3/23 16:22, Jocelyn Falempe wrote:
> This module displays a user friendly message when a kernel panic
> occurs. It currently doesn't contain any debug information,
> but that can be added later.
> 
> v2
>  * Use get_scanout_buffer() instead of the drm client API.
>   (Thomas Zimmermann)
>  * Add the panic reason to the panic message (Nerdopolis)
>  * Add an exclamation mark (Nerdopolis)
> 
> v3
>  * Rework the drawing functions, to write the pixels line by line and
>  to use the drm conversion helper to support other formats.
>  (Thomas Zimmermann)
> 
> v4
>  * Use drm_fb_r1_to_32bit for fonts (Thomas Zimmermann)
>  * Remove the default y to DRM_PANIC config option (Thomas Zimmermann)
>  * Add foreground/background color config option
>  * Fix the bottom lines not painted if the framebuffer height
>    is not a multiple of the font height.
>  * Automatically register the device to drm_panic, if the function
>    get_scanout_buffer exists. (Thomas Zimmermann)
> 
> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
> ---
>  drivers/gpu/drm/Kconfig     |  22 ++
>  drivers/gpu/drm/Makefile    |   1 +
>  drivers/gpu/drm/drm_drv.c   |   8 +
>  drivers/gpu/drm/drm_panic.c | 413 ++++++++++++++++++++++++++++++++++++
>  include/drm/drm_drv.h       |  14 ++
>  include/drm/drm_panic.h     |  41 ++++
>  6 files changed, 499 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_panic.c
>  create mode 100644 include/drm/drm_panic.h
> 

> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> new file mode 100644

> +static void draw_panic_device(struct drm_device *dev, const char *msg)
> +{
> +	struct drm_scanout_buffer sb;
> +
> +	if (dev->driver->get_scanout_buffer(dev, &sb))
> +		return;
> +	if (!drm_panic_line_buf)
> +		return;
> +

Unless something has changed since 2019 we need to make sure fbcon
hasn't already printed the panic to avoid jumbled output. See [1] for
more info.

Noralf.

[1]
https://lore.kernel.org/dri-devel/20190312095320.GX2665@phenom.ffwll.local/

> +	/* to avoid buffer overflow on drm_panic_line_buf */
> +	if (sb.width > DRM_PANIC_MAX_WIDTH)
> +		sb.width = DRM_PANIC_MAX_WIDTH;
> +
> +	draw_panic_static(&sb, msg);
> +}