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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: Thierry Reding <treding@nvidia.com>
This commit is contained in:
Thierry Reding 2015-07-21 16:38:11 +02:00
parent c4a2728852
commit 01f09f242e
2 changed files with 60 additions and 0 deletions
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55
drivers/gpu/drm/tegra/dp.c
View File

@ -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;
}

5
drivers/gpu/drm/tegra/dp.h
View File

@ -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