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Date:   Wed, 8 Jul 2020 02:12:29 +0300
From:   Imre Deak <imre.deak@intel.com>
To:     Lyude Paul <lyude@redhat.com>
Cc:     dri-devel@lists.freedesktop.org,
        Cooper Chiou <cooper.chiou@intel.com>,
        David Airlie <airlied@linux.ie>,
        intel-gfx@lists.freedesktop.org,
        Lucas De Marchi <lucas.demarchi@intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [Intel-gfx] [PATCH 2/2] drm/i915/mst: filter out the display
 mode exceed sink's capability
Message-ID: <20200707231229.GB22747@ideak-desk.fi.intel.com>
Reply-To: imre.deak@intel.com
References: <20200526182313.4005-1-lyude@redhat.com>
 <20200526182313.4005-3-lyude@redhat.com>
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On Tue, May 26, 2020 at 02:23:10PM -0400, Lyude Paul wrote:
> From: Lee Shawn C <shawn.c.lee@intel.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@60fps. DP 1.2 can support 4K@60fps
> because it did not surpass DP physical bandwidth limitation.
> Do modeset to 4k@60fps, 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.
> 
> v2: Using mgr->base.lock to protect full_pbn.
> v3: Add ctx lock.
> v4:
> * 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
> 
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Cooper Chiou <cooper.chiou@intel.com>
> Co-developed-by: Lyude Paul <lyude@redhat.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> Tested-by: Lee Shawn C <shawn.c.lee@intel.com>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 39 ++++++++++++++++++---
>  1 file changed, 35 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index d18b406f2a7d2..cf052095ad785 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -610,15 +610,42 @@ static int intel_dp_mst_get_modes(struct drm_connector *connector)
>  	return intel_dp_mst_get_ddc_modes(connector);
>  }
>  
> +static int
> +intel_dp_mst_mode_clock_exceeds_pbn_bw(struct drm_connector *connector,
> +				       struct drm_modeset_acquire_ctx *ctx,
> +				       int clock, int bpp)
> +{
> +	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 = (to_intel_connector(connector))->port;

					intel_connector

> +	int ret = MODE_OK;
> +
> +	if (!mgr)

As a NULL check this would be bogus, but also connector->mst_port and so
mst_mgr too should be always non-NULL?

> +		return ret;
> +
> +	ret = drm_modeset_lock(&mgr->base.lock, ctx);
> +	if (ret == -EDEADLK)
> +		return ret;
> +
> +	if (port->full_pbn &&

How could full_pbn be unset?

> +	    drm_dp_calc_pbn_mode(clock, bpp, false) > port->full_pbn)
> +		ret = MODE_CLOCK_HIGH;
> +
> +	return ret;
> +}
> +
>  static enum drm_mode_status
> -intel_dp_mst_mode_valid(struct drm_connector *connector,
> -			struct drm_display_mode *mode)
> +intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
> +			    struct drm_display_mode *mode,
> +			    struct drm_modeset_acquire_ctx *ctx)
>  {
>  	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;
>  	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;
> @@ -632,7 +659,11 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
>  	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
>  	mode_rate = intel_dp_link_required(mode->clock, 18);
>  
> -	/* TODO - validate mode against available PBN for link */
> +	ret = intel_dp_mst_mode_clock_exceeds_pbn_bw(connector, ctx,
> +						     mode->clock, 24);

Why 24 bpp and not 18?

Nit: could be checked after max_rate/max_dotclk for consistency.

> +	if (ret != MODE_OK)
> +		return ret;
> +
>  	if (mode->clock < 10000)
>  		return MODE_CLOCK_LOW;
>  
> @@ -671,7 +702,7 @@ 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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