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Commit cd9dde44 authored by Adam Jackson's avatar Adam Jackson Committed by Keith Packard
Browse files

drm/i915/dp: Fix the math in intel_dp_link_required 



The previous code was confused about units, which is pretty reasonable
given that the units themselves are confusing.

Signed-off-by: default avatarAdam Jackson <ajax@redhat.com>
Signed-off-by: default avatarKeith Packard <keithp@keithp.com>
parent f52c619a

drivers/gpu/drm/i915/intel_dp.c

+21 −5
Original line number Diff line number Diff line
@@ -184,9 +184,25 @@ intel_dp_link_clock(uint8_t link_bw) 
		return 162000;

}



/* I think this is a fiction */

/*

 * The units on the numbers in the next two are... bizarre.  Examples will

 * make it clearer; this one parallels an example in the eDP spec.

 *

 * intel_dp_max_data_rate for one lane of 2.7GHz evaluates as:

 *

 *     270000 * 1 * 8 / 10 == 216000

 *

 * The actual data capacity of that configuration is 2.16Gbit/s, so the

 * units are decakilobits.  ->clock in a drm_display_mode is in kilohertz -

 * or equivalently, kilopixels per second - so for 1680x1050R it'd be

 * 119000.  At 18bpp that's 2142000 kilobits per second.

 *

 * Thus the strange-looking division by 10 in intel_dp_link_required, to

 * get the result in decakilobits instead of kilobits.

 */



static int

intel_dp_link_required(struct drm_device *dev, struct intel_dp *intel_dp, int pixel_clock)

intel_dp_link_required(struct intel_dp *intel_dp, int pixel_clock)

{

	struct drm_crtc *crtc = intel_dp->base.base.crtc;

	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
@@ -195,7 +211,7 @@ intel_dp_link_required(struct drm_device *dev, struct intel_dp *intel_dp, int pi 
	if (intel_crtc)

		bpp = intel_crtc->bpp;



	return (pixel_clock * bpp + 7) / 8;

	return (pixel_clock * bpp + 9) / 10;

}



static int
@@ -223,7 +239,7 @@ intel_dp_mode_valid(struct drm_connector *connector, 
	/* only refuse the mode on non eDP since we have seen some weird eDP panels

	   which are outside spec tolerances but somehow work by magic */

	if (!is_edp(intel_dp) &&

	    (intel_dp_link_required(connector->dev, intel_dp, mode->clock)

	    (intel_dp_link_required(intel_dp, mode->clock)

	     > intel_dp_max_data_rate(max_link_clock, max_lanes)))

		return MODE_CLOCK_HIGH;
@@ -670,7 +686,7 @@ intel_dp_mode_fixup(struct drm_encoder *encoder, struct drm_display_mode *mode, 
		for (clock = 0; clock <= max_clock; clock++) {

			int link_avail = intel_dp_max_data_rate(intel_dp_link_clock(bws[clock]), lane_count);



			if (intel_dp_link_required(encoder->dev, intel_dp, mode->clock)

			if (intel_dp_link_required(intel_dp, mode->clock)

					<= link_avail) {

				intel_dp->link_bw = bws[clock];

				intel_dp->lane_count = lane_count;