linux-kernel - Re: [RFC] Try a bit harder to get output on the screen at panic time

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Message-ID: <vbf0pu1dqa60ojk7uuublww9.1275282082699@email.android.com>
Date:	Sun, 30 May 2010 22:03:10 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Airlie <airlied@...il.com>,
	James Simmons <jsimmons@...radead.org>
Subject: Re: [RFC] Try a bit harder to get output on the screen at panic
 time

I'll test again this week.  I still don't see how these small patches could cause issues with suspend/resume unless we set oops_in_progress during that time on your machine...

Jesse

Maxim Levitsky <maximlevitsky@...il.com> wrote:

>On Sat, 2010-05-22 at 01:26 +0300, Maxim Levitsky wrote: 
>> On Fri, 2010-05-21 at 15:02 -0700, Jesse Barnes wrote: 
>> > On Sat, 22 May 2010 00:57:30 +0300
>> > Maxim Levitsky <maximlevitsky@...il.com> wrote:
>> > 
>> > > On Fri, 2010-05-21 at 00:14 +0300, Maxim Levitsky wrote: 
>> > > > On Thu, 2010-05-20 at 09:28 -0700, Jesse Barnes wrote: 
>> > > > > On Thu, 20 May 2010 04:27:07 +0300
>> > > > > Maxim Levitsky <maximlevitsky@...il.com> wrote:
>> > > > > 
>> > > > > > On Thu, 2010-05-20 at 04:13 +0300, Maxim Levitsky wrote: 
>> > > > > > > On Wed, 2010-05-19 at 17:34 -0700, Jesse Barnes wrote: 
>> > > > > > > > On Fri, 9 Apr 2010 15:10:50 -0700
>> > > > > > > > Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
>> > > > > > > > 
>> > > > > > > > > This set of 3 patches makes it a little more likely we'll get panic
>> > > > > > > > > output onto the screen even when X is running, assuming a KMS enabled
>> > > > > > > > > stack anyway.
>> > > > > > > > > 
>> > > > > > > > > It gets me from a blank or very sparsely populated black screen at
>> > > > > > > > > panic time, to one including the full backtrace and panic output at
>> > > > > > > > > panic time (tested with "echo c > /proc/sysrq-trigger" from an X
>> > > > > > > > > session).
>> > > > > > > > > 
>> > > > > > > > > It doesn't cover every case; for instance I think it'll fail when X has
>> > > > > > > > > disabled the display, but those cases need to be handled with separate
>> > > > > > > > > patches anyway (need to add atomic DPMS paths for instance).
>> > > > > > > > > 
>> > > > > > > > > Anyway, please test these out and let me know if they work for you.
>> > > > > > > > 
>> > > > > > > > Ping Linus & Dave again.  Have you guys tried these?  Really, it's cool.
>> > > > > > > > 
>> > > > > > > Second that, just tested these patches, and these work perfectly.
>> > > > > > > One more reason for me to dump nvidia driver for nouveau.
>> > > > > > 
>> > > > > > 
>> > > > > > Unfortunately I spoke too soon.
>> > > > > > 
>> > > > > > 
>> > > > > > After suspend to ram, system doesn't properly resume now.
>> > > > > > 
>> > > > > > My system is based on nvidia G86, I use latest nouveau drivers, and
>> > > > > > suspend with compiz running.
>> > > > > > 
>> > > > > > I also patched kernel not to do vt switch on suspend/resume:
>> > > > > > 
>> > > > > > diff --git a/drivers/gpu/drm/nouveau/nouveau_state.c
>> > > > > > b/drivers/gpu/drm/nouveau/nouveau_state.c
>> > > > > > index 062b7f6..b3ef08b 100644
>> > > > > > --- a/drivers/gpu/drm/nouveau/nouveau_state.c
>> > > > > > +++ b/drivers/gpu/drm/nouveau/nouveau_state.c
>> > > > > > @@ -31,6 +31,7 @@
>> > > > > > #include "drm_crtc_helper.h"
>> > > > > > #include <linux/vgaarb.h>
>> > > > > > #include <linux/vga_switcheroo.h>
>> > > > > > +#include <linux/suspend.h>
>> > > > > > 
>> > > > > > #include "nouveau_drv.h"
>> > > > > > #include "nouveau_drm.h"
>> > > > > > @@ -771,6 +772,8 @@ int nouveau_load(struct drm_device *dev, unsigned
>> > > > > > long flags)
>> > > > > >                 int ret = nouveau_card_init(dev);
>> > > > > >                 if (ret)
>> > > > > >                         return ret;
>> > > > > > +
>> > > > > > +               pm_set_vt_switch(0);
>> > > > > >         }
>> > > > > > 
>> > > > > >         return 0;
>> > > > > 
>> > > > > Hm I don't see how my patches would have affected suspend/resume, since
>> > > > > they just add "oops_in_progress" checks to a few places.  Are you sure
>> > > > > something else isn't breaking your resume path?
>> > > > I am sure. I just reverted them, and everything works again.
>> > > > I refer to 3 patches in this thread.
>> > > In fact I might look a bit silly, but I applied these patches on top of
>> > > linus master tree + nouveau master, and suspend to ram works just fine.
>> > > 
>> > > Maybe it shows up when kgdb+kdb isn't compiled in or so.
>> > > Maybe it just triggered some bug in nouveau drivers...
>> > > 
>> > > 
>> > > (Note that I also enabled kgdb, and kdb, and breaking into kdb (SysRQ+g)
>> > > doesn't switch console mode, just hangs till I press 'g'.
>> > 
>> > Ok so it sounds like these particular patches are innocent?
>> > 
>> > As for kdb, I think the latest tree is probably missing the graphics
>> > switch support on the driver side...
>> In what part? nouveau or kdb?
>> 
>> Screen does switch to text mode and displays the backtrace on 'panic'
>> (Tested with sysrq+c).
>> (If kdb is enabled, screen doesn't switch, but allowing kdb to continue
>> via 'g' command eventually breaks into it.)
>
>Ping.
>
>Best regards,
>Maxim Levitsky
>
>