linux-kernel - RE: [Xen-devel] [Intel-gfx] [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type

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Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D125FCD743@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 11 Jul 2014 20:30:59 +0000
From:	"Tian, Kevin" <kevin.tian@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"Chen, Tiejun" <tiejun.chen@...el.com>,
	"Kay, Allen M" <allen.m.kay@...el.com>
Subject: RE: [Xen-devel] [Intel-gfx] [RFC][PATCH]
 gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class
 type

> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@...cle.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.

Thanks
Kevin
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