Re: [PATCH 06/18] drm/i915: Assume 400 MHz cdclk for the rest of gen4-7

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

On Mon, Nov 17, 2014 at 07:46:08PM +0100, Daniel Vetter wrote:
> On Mon, Nov 17, 2014 at 04:43:40PM +0200, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > We don't currently have cdclk extraction code for 965g,snb,ivb.
> > Let's assumee 400 MHz until we know better. That seems to match hints
> > in various vague documents. Whether that's good enough is not
> > entirely clear.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Hm, not sure whether these chips even had outputs which could drive this
> high really. And if we now start rejecting modes that previously worked
> (really unlikely imo) we'll get the regression reports and can fudge the
> numbers some more. So even without more spec hints I'm totally fine with
> going forward with this.

At least one IVB out there seems to agree with this 400MHz limit:
https://bugs.freedesktop.org/show_bug.cgi?id=85621

But it does look like we're also failing to respect the port limits
which according to BSpec are 315Mhz-388Mhz (depending on the port
and/or bpc) for IVB. So I guess you're right that the cdclk wouldn't
matter all that much if we actually checked the port limits.

Although there are also various sprite scaling/format related limits
we fail to check where the limit ends up being of the form cdclk*N
where N is something < 1.0. So having a decent approximation of the
cdclk around should be useful eventually.

-- 
Ville Syrjälä
Intel OTC
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