Re: [Xen-devel] [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jul 11, 2014 at 08:30:59PM +0000, Tian, Kevin wrote:
> > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> > Sent: Friday, July 11, 2014 12:42 PM
> > 
> > On Fri, Jul 11, 2014 at 08:29:56AM +0200, Daniel Vetter wrote:
> > > On Thu, Jul 10, 2014 at 09:08:24PM +0000, Tian, Kevin wrote:
> > > > actually I'm curious whether it's still necessary to __detect__ PCH. Could
> > > > we assume a 1:1 mapping between GPU and PCH, e.g. BDW already hard
> > > > code the knowledge:
> > > >
> > > >               } else if (IS_BROADWELL(dev)) {
> > > >                       dev_priv->pch_type = PCH_LPT;
> > > >                       dev_priv->pch_id =
> > > >
> > INTEL_PCH_LPT_LP_DEVICE_ID_TYPE;
> > > >                       DRM_DEBUG_KMS("This is Broadwell,
> > assuming "
> > > >                                     "LynxPoint LP PCH\n");
> > > >
> > > > Or if there is real usage on non-fixed mapping (not majority), could it be a
> > > > better option to have fixed mapping as a fallback instead of leaving as
> > > > PCH_NONE? Then even when Qemu doesn't provide a special tweaked
> > PCH,
> > > > the majority case just works.
> > >
> > > I guess we can do it, at least I haven't seen any strange combinations in
> > > the wild outside of Intel ...
> > 
> > How big is the QA matrix for this? Would it make sense to just
> > include the latest hardware (say going two generations back)
> > and ignore the older one?
> 
> suppose minimal or no QA effort on bare metal, if we only conservatively 
> change the fallback path which is today not supposed to function with 
> PCH_NONE. so it's only same amount of QA effort as whatever else is 
> proposed in this passthru upstreaming task. I agree no need to cover 
> older model, possibly just snb, ivb and hsw, but will leave Tiejun to answer 
> the overall goal.

Yeah, I'd be ok with the approach of using defaults if we can't recognize
the pch - if anyone screams we can either quirk or figure something else
out.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch