linux-kernel - Re: [PATCH] DRM / i915: Fix resume regression on MSI Wind U100 w/o KMS

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Date:	Sat, 9 Jan 2010 01:43:23 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Anholt <eric@...olt.net>,
	Zhenyu Wang <zhenyuw@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	dri-devel@...ts.sourceforge.net
Subject: Re: [PATCH] DRM / i915: Fix resume regression on MSI Wind U100 w/o KMS

On Saturday 09 January 2010, Jesse Barnes wrote:
> On Fri, 8 Jan 2010 16:06:59 -0800
> Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> 
> > On Fri, 8 Jan 2010 16:01:46 -0800 (PST)
> > Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > 
> > > 
> > > 
> > > On Sat, 9 Jan 2010, Rafael J. Wysocki wrote:
> > > >
> > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > 
> > > > Commit cbda12d77ea590082edb6d30bd342a67ebc459e0 (drm/i915:
> > > > implement new pm ops for i915), among other things, removed
> > > > the .suspend and .resume pointers from the struct drm_driver
> > > > object in i915_drv.c, which broke resume without KMS on my MSI
> > > > Wind U100.
> > > > 
> > > > Fix this by reverting that part of commit cbda12d77ea59.
> > > 
> > > Hmm. I get the feeling that perhaps the of the drm_driver callbacks
> > > was very muchintentional, and that the code presumably wants to be
> > > called purely through the PCI layer, and not through the "drm class"
> > > logic at all?
> > > 
> > > Your patch seems like it would always execute the silly class
> > > suspend even though we explicitly don't want to. And a much nicer
> > > fix would seem to register the thing properly as a PCI driver even
> > > if you don't then use KMS.
> > > 
> > > So it looks to me like the problem is that drm_init() will register
> > > the driver as a real PCI driver only if
> > > 
> > > 	driver->driver_features & DRIVER_MODESET
> > > 
> > > and otherwise it does that very odd "stealth mode manual scanning"
> > > thing which doesn't register it as a proper PCI driver.
> > > 
> > > So could we instead make that "disable KSM" _just_ disable the mode 
> > > setting part, not disable the "I'm a real driver" part?
> > 
> > Yeah, but that would be more invasive.  In the KMS case the driver
> > (which is registered as PCI) does a lot of the initialization that the
> > core takes care of in the non-KMS case, and some of it happens later
> > at ioctl time.  I'm afraid of that code since it seems like whenever
> > you change something obvious it subtly breaks an old userland.
> 
> Hm, maybe it's not as bad as I was afraid it was...  we already support
> i915.modeset=0 even on a KMS enabled driver, which should be fairly
> equivalent.  Rafael, if you build i915 with KMS enabled but modeset=0
> do you get the right suspend/resume behavior?

No, with modeset=0 it doesn't register the PCI driver as well.

Rafael
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