Re: [PATCH v8 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD aux

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Please fix the indenting on this. I've mentioned this already in my previous
reviews.

On Mon, 2019-08-26 at 19:16 +0000, Francis, David wrote:
> Received offline review from AMD MST DSC (Non-Linux) expert Wenjing Liu,
> giving me permission  to mark this patch
> Reviewed-by: Wenjing Liu <Wenjing.Liu@xxxxxxx>
> 
> ________________________________________
> From: David Francis <David.Francis@xxxxxxx>
> Sent: August 26, 2019 2:05 PM
> To: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Francis, David; Lyude Paul; Jani Nikula
> Subject: [PATCH v8 6/6] drm/dp_mst: Add helpers for MST DSC and virtual DPCD
> aux
> 
> 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
> 
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Signed-off-by: David Francis <David.Francis@xxxxxxx>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 152 ++++++++++++++++++++++++++
>  include/drm/drm_dp_mst_helper.h       |   2 +
>  2 files changed, 154 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 502923c24450..1fee92bd51f7 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4150,3 +4150,155 @@ 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)
> +               return false;
> +
> +       /* Virtual DP Sink (Internal Display Panel) */
> +       if (port->port_num >= 8 && port->dpcd_rev >= DP_DPCD_REV_14)
> +               return true;
> +
> +       /* DP-to-HDMI Protocol Converter */
> +       if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
> +                       !port->mcs &&
> +                       port->ldps &&
> +                       port->dpcd_rev >= DP_DPCD_REV_14)
> +               return true;
> +
> +       /* DP-to-DP */
> +       mutex_lock(&port->mgr->lock);
> +       if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
> +                       port->mstb &&
> +                       port->dpcd_rev >= DP_DPCD_REV_14 &&
> +                       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 && 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;
> +       }
> +
> +       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;
> 
>  /**
> --
> 2.17.1
> 
-- 
Cheers,
	Lyude Paul

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