Hi! Sorry this took me a little while to get back to, I had a couple of MST
regressions that I had to look into
On Sat, 2020-04-18 at 05:24 +0800, Lee Shawn C wrote:
> 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.
>
> Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Cooper Chiou <cooper.chiou@xxxxxxxxx>
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Signed-off-by: Lee Shawn C <shawn.c.lee@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_dp_mst.c | 24 ++++++++++++++++++++-
> 1 file changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 61605eb8c2af..68697f463dab 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -609,6 +609,26 @@ static int intel_dp_mst_get_modes(struct drm_connector
> *connector)
> return intel_dp_mst_get_ddc_modes(connector);
> }
>
> +static bool
> +intel_dp_mst_mode_clock_exceed_pbn_bandwidth(struct drm_connector
> *connector, 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;
> + bool ret = false;
> +
> + if (!mgr)
> + return ret;
> +
> + mutex_lock(&mgr->lock);
This isn't the right lock for this - mgr->lock protects the topology layout
(e.g. drm_dp_mst_port.mstb, drm_dp_mst_port.next, and
drm_dp_mst_branch.ports). port->full_pbn is protected under
&drm_dp_mst_topology_mgr.base.lock (not drm_dp_mst_topology_mgr.lock), so you
need to first add a version of .mode_valid() to struct
drm_connector_helper_funcs that accepts a drm_modeset_acquire_ctx so you can
use that to safely grab &drm_dp_mst_topology_mgr.base.lock.
> + if (port->full_pbn)
Also - there's no reason to check if (port->full_pbn) here, so long as you're
holding the right locks this should always be populated by the time we create
the drm_connector for the MST port (if it's not, that's a bug that needs to be
fixed).
> + ret = (drm_dp_calc_pbn_mode(clock, bpp, false) > port-
> >full_pbn);
Finally - I'd say we should probably have a separate patch to add a helper for
calculating the PBN and checking it against port->full_pbn. Maybe something
that looks like this:
int drm_dp_mst_mode_valid(struct drm_dp_mst_port *port, struct
drm_modeset_acquire_ctx *ctx, int clock, int bpp) {
int ret = MODE_VALID;
/* TODO: DSC support */
/* …try grabbing locks here…*/
if (drm_dp_calc_pbn_mode(clock, bpp, false) > port->full_pbn)
ret = MODE_CLOCK_HIGH;
return ret;
}
That way we might be able to add some checks for DSC capable connectors later
once I've migrated most of the DSC code from amdgpu into the MST helpers
> + mutex_unlock(&mgr->lock);
> +
> + return ret;
> +}
> +
> static enum drm_mode_status
> intel_dp_mst_mode_valid(struct drm_connector *connector,
> struct drm_display_mode *mode)
> @@ -631,7 +651,9 @@ 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 */
> + if (intel_dp_mst_mode_clock_exceed_pbn_bandwidth(connector, mode-
> >clock, 24))
> + return MODE_CLOCK_HIGH;
> +
> if (mode->clock < 10000)
> return MODE_CLOCK_LOW;
>
--
Cheers,
Lyude Paul (she/her)
Associate Software Engineer at Red Hat
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