Re: [PATCH 05/11] drm/i915: Rename BXT PORTA HPD defines

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Aug 26, 2015 at 09:59:13PM +0000, Runyan, Arthur J wrote:
> 
> >From: Ville Syrjälä [mailto:ville.syrjala@linux.intel.com]
> >> On Wed, Aug 26, 2015 at 04:13:52PM -0300, Paulo Zanoni wrote:
> ...
> >> Although the doc for LPT _suggests_ this is only for LPT:LP, it
> >> doesn't mark this bit as LPT:LP-specific just like it marks all the
> >> other LPT:LP-specific bits in every register, so I wonder if this is
> >> really LPT:LP or if there's another way to find this out, like some
> >> strap or VBT bit.
> >
> >Hmm. Indeed. There is that note about the enable being in the north
> >on DevLPT:H. I guess that's what gave me the idea for this patch. But
> >the rest of the text just talks about PCH being on the same package or
> >not. Not sure if the two conditions are entirely the same thing.
> >
> >For HSW the north register says we need this on DevHSW:ULT. For BDW it
> >refers us to a package type indication in FUSE_STRAP3, but the only
> >relevant looking bit is the ULT mode bit, which it also says is
> >currently unused and should be ignored :(
> >
> >Art, could you help us out here? How should we actually determine
> >(on HSW/BDW) whether to enable the DDI A HPD in the north, south,
> >or both?
> 
> The north and south hotplug control registers have text to try to explain this in the DDI A HPD enable fields, which I pasted below.  You always enable north.  You additionally enable south if CPU and PCH are in the same package.

OK thanks. That more or less matches my original understanding.

> 
> "This only applies to systems that have the CPU and PCH in the same package, where the DDI A HPD input is connected to the PCH and the HPD must be enabled in both the North Display Engine Registers HOTPLUG_CTL and the South Display Engine Registers SHOTPLUG_CTL.  The HPD status is found in North Display Engine Registers HOTPLUG_CTL.
> 
> On systems that have the CPU and PCH in separate packages, the DDI A HPD input is connected to the CPU, and the DDI A HPD input must be enabled in only the North Display Engine Registers HOTPLUG_CTL."
> 
> That fuse may not be correct on all SKUs, but I assume you have other ways to recognize what kind of package it is.  I originally listed out ULT and ULX, but it became more complicated with BDW.

I'm not aware of any way of identifying the package type. My original
assumption was LPT-LP -> MCP, LPT-H -> separate package, and most of
the material I've managed to dig up would seem to support that. But
it's hard to be sure.

-- 
Ville Syrjälä
Intel OTC
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