diff options
| author | Thierry Reding <treding@nvidia.com> | 2015-07-21 16:38:11 +0200 |
|---|---|---|
| committer | Thierry Reding <treding@nvidia.com> | 2019-10-28 11:18:52 +0100 |
| commit | 01f09f242eb5cb194a88cef669a099fa10fcb3f0 (patch) | |
| tree | dcde81cee2ec727c77eb0bd790b956a32d33e133 /drivers/gpu/drm/tegra | |
| parent | c4a27288520d35e7e6acc6e36fba4585e1bddde6 (diff) | |
| download | linux-01f09f242eb5cb194a88cef669a099fa10fcb3f0.tar.bz2 | |
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>
Diffstat (limited to 'drivers/gpu/drm/tegra')
| -rw-r--r-- | drivers/gpu/drm/tegra/dp.c | 55 | ||||
| -rw-r--r-- | drivers/gpu/drm/tegra/dp.h | 5 |
2 files changed, 60 insertions, 0 deletions
diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c index 638081b568f4..e9a5db77a2dc 100644 --- a/drivers/gpu/drm/tegra/dp.c +++ b/drivers/gpu/drm/tegra/dp.c @@ -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; +} diff --git a/drivers/gpu/drm/tegra/dp.h b/drivers/gpu/drm/tegra/dp.h index 1fe2d4f45ba3..e07b9a1e43d8 100644 --- a/drivers/gpu/drm/tegra/dp.h +++ b/drivers/gpu/drm/tegra/dp.h @@ -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 |