[PATCH v9 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

[Jani Nikula]

On Tue, 27 Aug 2019, David Francis <David.Francis at amd.com> wrote:
> Add drm_dp_mst_dsc_aux_for_port. To enable DSC, the DSC_ENABLED
> register might have to be written on the leaf port's DPCD,
> its parent's DPCD, or the MST manager's DPCD. This function
> finds the correct aux for the job.
>
> As part of this, add drm_dp_mst_is_virtual_dpcd. Virtual DPCD
> is a DP feature new in DP v1.4, which exposes certain DPCD
> registers on virtual ports.
>
> v2: Remember to unlock mutex on all paths
> v3: Refactor to match coding style and increase brevity
>
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Harry Wentland <harry.wentland at amd.com>
> Reviewed-by: Wenjing Liu <Wenjing.Liu at amd.com>
> Signed-off-by: David Francis <David.Francis at amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 153 ++++++++++++++++++++++++++
>  include/drm/drm_dp_mst_helper.h       |   2 +
>  2 files changed, 155 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 502923c24450..e24dba276119 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4150,3 +4150,156 @@ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
>  {
>  	i2c_del_adapter(&aux->ddc);
>  }
> +
> +/**
> + * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
> + * @port: The port to check
> + *
> + * A single physical MST hub object can be represented in the topology
> + * by multiple branches, with virtual ports between those branches.
> + *
> + * As of DP1.4, An MST hub with internal (virtual) ports must expose
> + * certain DPCD registers over those ports. See sections 2.6.1.1.1
> + * and 2.6.1.1.2 of Display Port specification v1.4 for details.
> + *
> + * May acquire mgr->lock
> + *
> + * Returns:
> + * true if the port is a virtual DP peer device, false otherwise
> + */
> +static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
> +{
> +	struct drm_dp_mst_port *downstream_port;
> +
> +	if (!port || port->dpcd_rev < DP_DPCD_REV_14)
> +		return false;
> +
> +	/* Virtual DP Sink (Internal Display Panel) */
> +	if (port->port_num >= 8)
> +		return true;
> +
> +	/* DP-to-HDMI Protocol Converter */
> +	if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
> +	    !port->mcs &&
> +	    port->ldps)
> +		return true;
> +
> +	/* DP-to-DP */
> +	mutex_lock(&port->mgr->lock);
> +	if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
> +	    port->mstb &&
> +	    port->mstb->num_ports == 2) {
> +		list_for_each_entry(downstream_port, &port->mstb->ports, next) {
> +			if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
> +			    !downstream_port->input) {
> +				mutex_unlock(&port->mgr->lock);
> +				return true;
> +			}
> +		}
> +	}
> +	mutex_unlock(&port->mgr->lock);
> +
> +	return false;
> +}
> +
> +/**
> + * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
> + * @port: The port to check. A leaf of the MST tree with an attached display.
> + *
> + * Depending on the situation, DSC may be enabled via the endpoint aux,
> + * the immediately upstream aux, or the connector's physical aux.
> + *
> + * This is both the correct aux to read DSC_CAPABILITY and the
> + * correct aux to write DSC_ENABLED.
> + *
> + * This operation can be expensive (up to four aux reads), so
> + * the caller should cache the return.
> + *
> + * Returns:
> + * NULL if DSC cannot be enabled on this port, otherwise the aux device
> + */
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
> +{
> +	struct drm_dp_mst_port *immediate_upstream_port;
> +	struct drm_dp_mst_port *fec_port;
> +	struct drm_dp_desc *desc = NULL;
> +
> +	if (!port)
> +		return NULL;
> +
> +	if (port->parent)
> +		immediate_upstream_port = port->parent->port_parent;
> +	else
> +		immediate_upstream_port = NULL;
> +
> +	fec_port = immediate_upstream_port;
> +	while (fec_port) {
> +		/*
> +		 * Each physical link (i.e. not a virtual port) between the
> +		 * output and the primary device must support FEC
> +		 */
> +		if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
> +				!fec_port->fec_capable)
> +			return NULL;
> +
> +		fec_port = fec_port->parent->port_parent;
> +	}
> +
> +	/* DP-to-DP peer device */
> +	if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
> +		u8 upstream_dsc;
> +		u8 endpoint_dsc;
> +		u8 endpoint_fec;
> +
> +		if (drm_dp_dpcd_read(&port->aux,
> +				     DP_DSC_SUPPORT, &endpoint_dsc, 1) < 0)
> +			return NULL;
> +		if (drm_dp_dpcd_read(&port->aux,
> +				     DP_FEC_CAPABILITY, &endpoint_fec, 1) < 0)
> +			return NULL;
> +		if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
> +				     DP_DSC_SUPPORT, &upstream_dsc, 1) < 0)
> +			return NULL;
> +
> +		/* Enpoint decompression with DP-to-DP peer device */
> +		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
> +		    (endpoint_fec & DP_FEC_CAPABLE) &&
> +		    (upstream_dsc & 0x2) /* DSC passthrough */)
> +			return &port->aux;
> +
> +		/* Virtual DPCD decompression with DP-to-DP peer device */
> +		return &immediate_upstream_port->aux;
> +	}
> +
> +	/* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
> +	if (drm_dp_mst_is_virtual_dpcd(port))
> +		return &port->aux;
> +
> +	/*
> +	 * Synaptics quirk
> +	 * Applies to ports for which:
> +	 * - Physical aux has Synaptics OUI
> +	 * - DPv1.4 or higher
> +	 * - Port is on primary branch device
> +	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
> +	 */
> +	if (!drm_dp_read_desc(port->mgr->aux, desc, true))
> +		return false;
> +
> +	if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD &&
> +	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) &&
> +	    port->parent == port->mgr->mst_primary) {
> +		u8 downstreamport;
> +
> +		drm_dp_dpcd_read(&port->aux, DP_DOWNSTREAMPORT_PRESENT,
> +				 &downstreamport, 1);
> +
> +		if ((downstreamport & DP_DWN_STRM_PORT_PRESENT) &&
> +		   ((downstreamport & DP_DWN_STRM_PORT_TYPE_MASK)
> +		     != DP_DWN_STRM_PORT_TYPE_ANALOG))
> +			return port->mgr->aux;
> +	}

I would've put the quirk definition from patch 5 and the quirk handling
above together into a separate patch. The current patch would be about
how things should work in theory, and another patch on top would be
about how reality interferes with theory, and you have to quirk stuff to
make it actually work.

The whole point about splitting the quirk off was that it's a separate
functional change. What if the quirk turns out to be a mistake?  Just
revert the whole thing. That would be impossible with this split.

I don't know if I care enough to insist. *shrug*


BR,
Jani.



> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index f113ae04fa88..4cf738545dfb 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -673,6 +673,8 @@ int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
>  
> +struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port);
> +
>  extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
>  
>  /**

-- 
Jani Nikula, Intel Open Source Graphics Center