[Intel-gfx] [PATCH RESEND 9/9] drm/i915: set proper N/M in modeset

[Ville Syrjälä]

On Thu, Oct 20, 2016 at 02:34:34PM +0300, Jani Nikula wrote:
> On Thu, 20 Oct 2016, "Yang, Libin" <libin.yang at intel.com> wrote:
> >> >> Any particular reason these M/N values are half of what they're in
> >> >> table
> >> >> 2-104 of DP 1.4 spec? (Admittedly the table is an informative
> >> >> example.)
> >> >
> >> > For HDMI, we found only set N is enough. HW then can handle the
> >> remaining.
> >> 
> >> I meant, the M and N values in this part of the dp_aud_n_m table are 1/2 of
> >> what they are in the DP spec table. Why?
> >
> > Which table are you meaning? I calculate the values myself. I didn't find the
> > full table in DP spec. I only find the table for 270MHz and 162MHz in 
> > Table 2-50: Examples of Maud and Naud Values
> 
> Table 2-104 in DP 1.4. Maybe you're looking at an older version of the
> spec.

So it looks like they used the same M value for all link frequencies
in that example, which for 540M ends up being double what the minimal
accurate value is. But as both M and N are doubled the ratio is still
exactly the same.

And there is indeed a 64k and 128k bitrates added as well. Those are
not classified under HBR audio. But as those can't be expressed via
short audio descriptors in the EDID, I don't think they would be
accepted by ALSA. Or am I wrong? I do wonder how they are supposed to be
used though since there must be some way for the sink to advertise
them, otherwise I can't see the point in adding them.

-- 
Ville Syrjälä
Intel OTC