[RFC PATCH] drm/fb: drop panic handling

[Daniel Vetter]

On Thu, Jul 09, 2015 at 01:15:34PM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied at redhat.com>
> 
> This really doesn't seem to have much chance of working anymore,
> 
> esp for irq context, qxl at least tries to talk to the hw,
> and waits for irqs, and fails.
> 
> with runtime pm and other stuff I think we should just
> bail on this for now.
> 
> Signed-off-by: Dave Airlie <airlied at redhat.com>

Yeah concurred that this has become hopeless. Also this would allow us to
drop an pretension in i915 to still support this which means we can stop
checking drm_can_sleep in our wait_for macros. Which has papered over some
pretty serious bugs.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

There's one more though, we can get into the fbdev callbacks through a
pretty impressive chain:

panic() -> bust_spinlock() -> console_unblank() -> pass the trylock ->
	c->unblank() -> unblank_screen() (now in vt/vt.c) ->
		vc_sw->con_blank() -> fbcon_blank()

To make this really complete I think we also need to sprinkle

	if (oops_in_progress)
		return;

over all the fbdev entry points we have in drm_fbdev_helper.c plus all the
ones in drivers which have their own (qxl, udl, i915 are the ones I know
of).

Cheers, Daniel

> ---
>  drivers/gpu/drm/drm_fb_helper.c | 26 --------------------------
>  1 file changed, 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index cac4229..eaf652b 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -429,24 +429,6 @@ static bool drm_fb_helper_force_kernel_mode(void)
>  	return error;
>  }
>  
> -static int drm_fb_helper_panic(struct notifier_block *n, unsigned long ununsed,
> -			void *panic_str)
> -{
> -	/*
> -	 * It's a waste of time and effort to switch back to text console
> -	 * if the kernel should reboot before panic messages can be seen.
> -	 */
> -	if (panic_timeout < 0)
> -		return 0;
> -
> -	pr_err("panic occurred, switching back to text console\n");
> -	return drm_fb_helper_force_kernel_mode();
> -}
> -
> -static struct notifier_block paniced = {
> -	.notifier_call = drm_fb_helper_panic,
> -};
> -
>  static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
>  {
>  	struct drm_device *dev = fb_helper->dev;
> @@ -672,9 +654,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
>  	if (!list_empty(&fb_helper->kernel_fb_list)) {
>  		list_del(&fb_helper->kernel_fb_list);
>  		if (list_empty(&kernel_fb_helper_list)) {
> -			pr_info("drm: unregistered panic notifier\n");
> -			atomic_notifier_chain_unregister(&panic_notifier_list,
> -							 &paniced);
>  			unregister_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
>  		}
>  	}
> @@ -1109,12 +1088,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  	dev_info(fb_helper->dev->dev, "fb%d: %s frame buffer device\n",
>  			info->node, info->fix.id);
>  
> -	/* Switch back to kernel console on panic */
> -	/* multi card linked list maybe */
>  	if (list_empty(&kernel_fb_helper_list)) {
> -		dev_info(fb_helper->dev->dev, "registered panic notifier\n");
> -		atomic_notifier_chain_register(&panic_notifier_list,
> -					       &paniced);
>  		register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
>  	}
>  
> -- 
> 2.4.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch