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Message-ID: <20200710222447.GB29318@ideak-desk.fi.intel.com>
Date: Sat, 11 Jul 2020 01:24:47 +0300
From: Imre Deak <imre.deak@...el.com>
To: Lyude Paul <lyude@...hat.com>
Cc: intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
Lee Shawn C <shawn.c.lee@...el.com>,
Manasi Navare <manasi.d.navare@...el.com>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Ville Syrjala <ville.syrjala@...ux.intel.com>,
Cooper Chiou <cooper.chiou@...el.com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
José Roberto de Souza
<jose.souza@...el.com>, Lucas De Marchi <lucas.demarchi@...el.com>,
Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@...el.com>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] drm/i915/mst: filter out the display mode exceed
sink's capability
On Fri, Jul 10, 2020 at 03:31:44PM -0400, Lyude Paul wrote:
> From: Lee Shawn C <shawn.c.lee@...el.com>
>
> So far, max dot clock rate for MST mode rely on physcial
> bandwidth limitation. It would caused compatibility issue
> if source display resolution exceed MST hub output ability.
>
> For example, source DUT had DP 1.2 output capability.
> And MST docking just support HDMI 1.4 spec. When a HDMI 2.0
> monitor connected. Source would retrieve EDID from external
> and get max resolution 4k@...ps. DP 1.2 can support 4K@...ps
> because it did not surpass DP physical bandwidth limitation.
> Do modeset to 4k@...ps, source output display data but MST
> docking can't output HDMI properly due to this resolution
> already over HDMI 1.4 spec.
>
> Refer to commit <fcf463807596> ("drm/dp_mst: Use full_pbn
> instead of available_pbn for bandwidth checks").
> Source driver should refer to full_pbn to evaluate sink
> output capability. And filter out the resolution surpass
> sink output limitation.
>
> Changes since v1:
> * Using mgr->base.lock to protect full_pbn.
> Changes since v2:
> * Add ctx lock.
> Changes since v3:
> * s/intel_dp_mst_mode_clock_exceed_pbn_bandwidth/
> intel_dp_mst_mode_clock_exceeds_pbn_bw/
> * Use the new drm_connector_helper_funcs.mode_valid_ctx to properly pipe
> down the drm_modeset_acquire_ctx that the probe helpers are using, so
> we can safely grab &mgr->base.lock without deadlocking
> Changes since v4:
> * Move drm_dp_calc_pbn_mode(mode->clock, bpp, false) > port->full_pbn
> check
> * Fix the bpp we use in drm_dp_calc_pbn_mode()
> * Drop leftover (!mgr) check
> * Don't check for if full_pbn is unset. To be clear - it _can_ be unset,
> but if it is then it's certainly a bug in DRM or a non-compliant sink
> as full_pbn should always be populated by the time we call
> ->mode_valid_ctx.
> We should workaround non-compliant sinks with full_pbn=0, but that
> should happen in the DP MST helpers so we can estimate the full_pbn
> value as best we can.
I guess when the connector gets unplugged full_pbn would also get reset
but pruning all modes in that case is ok.
>
> Cc: Manasi Navare <manasi.d.navare@...el.com>
> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> Cc: Ville Syrjala <ville.syrjala@...ux.intel.com>
> Cc: Cooper Chiou <cooper.chiou@...el.com>
> Co-developed-by: Lyude Paul <lyude@...hat.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee@...el.com>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
Reviewed-and-tested-by: Imre Deak <imre.deak@...el.com>
> ---
> drivers/gpu/drm/i915/display/intel_dp_mst.c | 55 ++++++++++++++-------
> 1 file changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index bdc19b04b2c10..a2d91a4997001 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -639,39 +639,60 @@ static int intel_dp_mst_get_modes(struct drm_connector *connector)
> return intel_dp_mst_get_ddc_modes(connector);
> }
>
> -static enum drm_mode_status
> -intel_dp_mst_mode_valid(struct drm_connector *connector,
> - struct drm_display_mode *mode)
> +static int
> +intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
> + struct drm_display_mode *mode,
> + struct drm_modeset_acquire_ctx *ctx,
> + enum drm_mode_status *status)
> {
> struct drm_i915_private *dev_priv = to_i915(connector->dev);
> struct intel_connector *intel_connector = to_intel_connector(connector);
> struct intel_dp *intel_dp = intel_connector->mst_port;
> + struct drm_dp_mst_topology_mgr *mgr = &intel_dp->mst_mgr;
> + struct drm_dp_mst_port *port = intel_connector->port;
> + const int min_bpp = 18;
> int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
> int max_rate, mode_rate, max_lanes, max_link_clock;
> + int ret;
>
> - if (drm_connector_is_unregistered(connector))
> - return MODE_ERROR;
> + if (drm_connector_is_unregistered(connector)) {
> + *status = MODE_ERROR;
> + return 0;
> + }
>
> - if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
> - return MODE_NO_DBLESCAN;
> + if (mode->flags & DRM_MODE_FLAG_DBLSCAN) {
> + *status = MODE_NO_DBLESCAN;
> + return 0;
> + }
>
> max_link_clock = intel_dp_max_link_rate(intel_dp);
> max_lanes = intel_dp_max_lane_count(intel_dp);
>
> max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
> - mode_rate = intel_dp_link_required(mode->clock, 18);
> + mode_rate = intel_dp_link_required(mode->clock, min_bpp);
>
> - /* TODO - validate mode against available PBN for link */
> - if (mode->clock < 10000)
> - return MODE_CLOCK_LOW;
> + ret = drm_modeset_lock(&mgr->base.lock, ctx);
> + if (ret)
> + return ret;
>
> - if (mode->flags & DRM_MODE_FLAG_DBLCLK)
> - return MODE_H_ILLEGAL;
> + if (mode_rate > max_rate || mode->clock > max_dotclk ||
> + drm_dp_calc_pbn_mode(mode->clock, min_bpp, false) > port->full_pbn) {
> + *status = MODE_CLOCK_HIGH;
> + return 0;
> + }
> +
> + if (mode->clock < 10000) {
> + *status = MODE_CLOCK_LOW;
> + return 0;
> + }
>
> - if (mode_rate > max_rate || mode->clock > max_dotclk)
> - return MODE_CLOCK_HIGH;
> + if (mode->flags & DRM_MODE_FLAG_DBLCLK) {
> + *status = MODE_H_ILLEGAL;
> + return 0;
> + }
>
> - return intel_mode_valid_max_plane_size(dev_priv, mode);
> + *status = intel_mode_valid_max_plane_size(dev_priv, mode);
> + return 0;
> }
>
> static struct drm_encoder *intel_mst_atomic_best_encoder(struct drm_connector *connector,
> @@ -700,7 +721,7 @@ intel_dp_mst_detect(struct drm_connector *connector,
>
> static const struct drm_connector_helper_funcs intel_dp_mst_connector_helper_funcs = {
> .get_modes = intel_dp_mst_get_modes,
> - .mode_valid = intel_dp_mst_mode_valid,
> + .mode_valid_ctx = intel_dp_mst_mode_valid_ctx,
> .atomic_best_encoder = intel_mst_atomic_best_encoder,
> .atomic_check = intel_dp_mst_atomic_check,
> .detect_ctx = intel_dp_mst_detect,
> --
> 2.26.2
>
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