Commit 01f09f24 authored by Thierry Reding's avatar Thierry Reding
Browse files

drm/tegra: dp: Add drm_dp_link_choose() helper 



This helper chooses an appropriate configuration, according to the
bitrate requirements of the video mode and the capabilities of the
DisplayPort sink.

Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
parent c4a27288

drivers/gpu/drm/tegra/dp.c

+55 −0
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
 * Copyright (C) 2015 Rob Clark

 */



#include <drm/drm_crtc.h>

#include <drm/drm_dp_helper.h>

#include <drm/drm_print.h>
@@ -234,3 +235,57 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link) 


	return 0;

}



/**

 * drm_dp_link_choose() - choose the lowest possible configuration for a mode

 * @link: DRM DP link object

 * @mode: DRM display mode

 * @info: DRM display information

 *

 * According to the eDP specification, a source should select a configuration

 * with the lowest number of lanes and the lowest possible link rate that can

 * match the bitrate requirements of a video mode. However it must ensure not

 * to exceed the capabilities of the sink.

 *

 * Returns: 0 on success or a negative error code on failure.

 */

int drm_dp_link_choose(struct drm_dp_link *link,

		       const struct drm_display_mode *mode,

		       const struct drm_display_info *info)

{

	/* available link symbol clock rates */

	static const unsigned int rates[3] = { 162000, 270000, 540000 };

	/* available number of lanes */

	static const unsigned int lanes[3] = { 1, 2, 4 };

	unsigned long requirement, capacity;

	unsigned int rate = link->max_rate;

	unsigned int i, j;



	/* bandwidth requirement */

	requirement = mode->clock * info->bpc * 3;



	for (i = 0; i < ARRAY_SIZE(lanes) && lanes[i] <= link->max_lanes; i++) {

		for (j = 0; j < ARRAY_SIZE(rates) && rates[j] <= rate; j++) {

			/*

			 * Capacity for this combination of lanes and rate,

			 * factoring in the ANSI 8B/10B encoding.

			 *

			 * Link rates in the DRM DP helpers are really link

			 * symbol frequencies, so a tenth of the actual rate

			 * of the link.

			 */

			capacity = lanes[i] * (rates[j] * 10) * 8 / 10;



			if (capacity >= requirement) {

				DRM_DEBUG_KMS("using %u lanes at %u kHz (%lu/%lu kbps)\n",

					      lanes[i], rates[j], requirement,

					      capacity);

				link->lanes = lanes[i];

				link->rate = rates[j];

				return 0;

			}

		}

	}



	return -ERANGE;

}

drivers/gpu/drm/tegra/dp.h

+5 −0
Original line number Diff line number Diff line
@@ -9,6 +9,8 @@ 


#include <linux/types.h>



struct drm_display_info;

struct drm_display_mode;

struct drm_dp_aux;



/**
@@ -91,5 +93,8 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link); 
int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);

int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link);

int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);

int drm_dp_link_choose(struct drm_dp_link *link,

		       const struct drm_display_mode *mode,

		       const struct drm_display_info *info);



#endif