[Intel-gfx] [PATCH 1/7 resend] drm/i915: Add the support of eDP on DP-D for Ibex/CPT

[Zhenyu Wang]

On 2010.06.14 10:28:55 -0400, Adam Jackson wrote:
> On Sat, 2010-06-12 at 09:28 +0100, Chris Wilson wrote:
> > On Sat, 12 Jun 2010 14:32:21 +0800, Zhenyu Wang <zhenyuw at linux.intel.com> wrote:
> > >  static void
> > > -intel_dp_compute_m_n(int bytes_per_pixel,
> > > +intel_dp_compute_m_n(int bpp,
> > >  		     int nlanes,
> > >  		     int pixel_clock,
> > >  		     int link_clock,
> > >  		     struct intel_dp_m_n *m_n)
> > >  {
> > >  	m_n->tu = 64;
> > > -	m_n->gmch_m = pixel_clock * bytes_per_pixel;
> > > +	m_n->gmch_m = (pixel_clock * bpp) >> 3;
> > >  	m_n->gmch_n = link_clock * nlanes;
> > >  	intel_reduce_ratio(&m_n->gmch_m, &m_n->gmch_n);
> > >  	m_n->link_m = pixel_clock;
> > 
> > This rounds the gmch_m down. Is this correct?
> 
> It's not, though thanks to the magic of PLLs it's probably close enough.
> However...
> 
> > And how close to overflow is pixel_clock today?
> 
> % echo $(( (2 ** 31 - 1) / 24. ))
> 89478485.291666672
> 
> 89MHz isn't even a single LVDS link.  Looks like that math needs to be
> 64-bit.
> 

Right, 64-bit math is needed for this like what has been done for FDI
link.

-- 
Open Source Technology Center, Intel ltd.

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