Re: [PATCH v3 2/6] drm/i915: Remove the link rate and lane count loop in compute config

[Manasi Navare <manasi.d.navare@intel.com>]

On Mon, Sep 26, 2016 at 04:41:27PM +0300, Jani Nikula wrote:
> On Fri, 16 Sep 2016, Manasi Navare <manasi.d.navare@intel.com> wrote:
> > While configuring the pipe during modeset, it should use
> > max clock and max lane count and reduce the bpp until
> > the requested mode rate is less than or equal to
> > available link BW.
> > This is required to pass DP Compliance.
> 
> As I wrote in reply to patch 1/6, this is not a DP spec requirement. The
> link policy maker can freely choose the link parameters as long as the
> sink supports them.
> 
> BR,
> Jani.
> 
>

Thanks for your review feedback.
This change was driven by Video Pattern generation tests in CTS spec. Eg: In
test 4.3.3.1, the test requests 640x480 @ max link rate of 2.7Gbps and 4 lanes.
The test will pass if it sets the link rate to 2.7 and lane count = 4.
But in the existing implementation, this video mode request triggers a modeset
but the compute_config function starts with the lowest link rate and lane count and
trains the link at 1.62 and 4 lanes which does not match the expeced values of link
rate = 2.7 and lane count = 4 and the test fails. 

Regards
Manasi
 
> >
> > v3:
> > * Add Debug print if requested mode cannot be supported
> > during modeset (Dhinakaran Pandiyan)
> > v2:
> > * Removed the loop since we use max values of clock
> > and lane count (Dhinakaran Pandiyan)
> >
> > Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 22 ++++++++--------------
> >  1 file changed, 8 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index d81c67cb..65b4559 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -1644,23 +1644,17 @@ intel_dp_compute_config(struct intel_encoder *encoder,
> >  	for (; bpp >= 6*3; bpp -= 2*3) {
> >  		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
> >  						   bpp);
> > +		clock = max_clock;
> > +		lane_count = max_lane_count;
> > +		link_clock = common_rates[clock];
> > +		link_avail = intel_dp_max_data_rate(link_clock,
> > +						    lane_count);
> >  
> > -		for (clock = min_clock; clock <= max_clock; clock++) {
> > -			for (lane_count = min_lane_count;
> > -				lane_count <= max_lane_count;
> > -				lane_count <<= 1) {
> > -
> > -				link_clock = common_rates[clock];
> > -				link_avail = intel_dp_max_data_rate(link_clock,
> > -								    lane_count);
> > -
> > -				if (mode_rate <= link_avail) {
> > -					goto found;
> > -				}
> > -			}
> > -		}
> > +		if (mode_rate <= link_avail)
> > +			goto found;
> >  	}
> >  
> > +	DRM_DEBUG_KMS("Requested Mode Rate not supported\n");
> >  	return false;
> >  
> >  found:
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
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