[PATCH v2 1/3] drm: Add support for panic message output

[Noralf Trønnes]

Den 11.03.2019 20.29, skrev Daniel Vetter:
> On Mon, Mar 11, 2019 at 08:23:38PM +0100, Daniel Vetter wrote:
>> On Mon, Mar 11, 2019 at 06:42:16PM +0100, Noralf Trønnes wrote:
>>> This adds support for outputting kernel messages on panic().
>>> A kernel message dumper is used to dump the log. The dumper iterates
>>> over each DRM device and it's crtc's to find suitable framebuffers.
>>>
>>> All the other dumpers are run before this one except mtdoops.
>>> Only atomic drivers are supported.
>>>
>>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>

<snip>

>>> +static void drm_panic_try_dev(struct drm_device *dev, struct kmsg_dumper *dumper)
>>> +{
>>> +	struct drm_framebuffer *fb;
>>> +	struct drm_plane *plane;
>>> +	struct drm_crtc *crtc;
>>> +
>>> +	if (!drm_core_check_feature(dev, DRIVER_ATOMIC))
>>> +		return;
>>> +
>>> +	if (dumper->max_reason == KMSG_DUMP_OOPS)
>>> +		pr_info("%s: %s on minor %d\n", __func__, dev->driver->name,
>>> +			dev->primary->index);
>>> +
>>> +	drm_for_each_crtc(crtc, dev) {
>>> +		if (!ww_mutex_trylock(&crtc->mutex.mutex))
>>> +			continue;
>>> +
>>> +		if (!crtc->enabled || !crtc->primary)
>>> +			goto crtc_unlock;
>>> +
>>> +		if (!crtc->state || !crtc->state->active)
>>> +			goto crtc_unlock;
>>> +
>>> +		plane = crtc->primary;
>>> +		if (!ww_mutex_trylock(&plane->mutex.mutex))
>>> +			goto crtc_unlock;
>>> +
>>> +		/*
>>> +		 * TODO: Should we check plane_state->visible?
>>> +		 * It is not set on vc4
>>
>> I think we should. We should also check whether that primary is connected
>> to the crtc (some hw you can reassign planes freely between crtc, and the
>> crtc->primary pointer is only used for compat with legacy ioctl).
>>
>>> +		if (!plane->state || !plane->state->visible)
>>> +		 */
>>> +		if (!plane->state)
>>> +			goto plane_unlock;
>>> +
>>> +		fb = plane->state->fb;
>>> +		if (!fb || !fb->funcs->panic_vmap)
>>
>> Docs says this is optional, doesn't seem to be all that optional. I'd
>> check for this or a driver-specific ->panic_draw_xy instead.
>>> +			goto plane_unlock;
>>> +
>>> +		/*
>>> +		 * fbcon puts out panic messages so stay away to avoid jumbled
>>> +		 * output. If vc->vc_mode != KD_TEXT fbcon won't put out
>>> +		 * messages (see vt_console_print).
>>> +		 */
>>> +		if (dev->fb_helper && dev->fb_helper->fb == fb)
> 
> This is a bit a layering violation. Could we instead tell fbcon that it
> shouldn't do panic handling for drm drivers? I think that would resolve
> this overlap here in a much cleaner way. drm fbdev helpers already have
> lots of oops_in_progress checks all over to make sure fbcon doesn't do
> anything bad. That only leaves the actual rendering, which I think we can
> stop too with a simple flag.
> 
> Ofc only for atomic drivers which have this panic handling mode here
> implemented.

There used to be a fbdev flag FBINFO_CAN_FORCE_OUTPUT that controlled
vc->vc_panic_force_write, but it's gone now I see.

Noralf.

> -Daniel
> 
>>> +			goto plane_unlock;
>>> +
>>> +		drm_panic_kmsg_render_screen(plane, dumper);
>>> +plane_unlock:
>>> +		ww_mutex_unlock(&plane->mutex.mutex);
>>> +crtc_unlock:
>>> +		ww_mutex_unlock(&crtc->mutex.mutex);
>>> +	}
>>> +}