Re: [PATCH v2 07/18] drm/dp: Pimp drm_dp_downstream_max_bpc()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 08, 2020 at 01:51:56PM -0400, Lyude Paul wrote:
> On Fri, 2020-09-04 at 14:53 +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Deal with more cases in drm_dp_downstream_max_bpc():
> > - DPCD 1.0 -> assume 8bpc for non-DP
> > - DPCD 1.1+ DP (or DP++ with DP sink) -> allow anything
> > - DPCD 1.1+ TMDS -> check the caps, assume 8bpc if the value is crap
> > - anything else -> assume 8bpc
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c               | 69 +++++++++++--------
> >  .../drm/i915/display/intel_display_debugfs.c  |  3 +-
> >  drivers/gpu/drm/i915/display/intel_dp.c       |  2 +-
> >  include/drm/drm_dp_helper.h                   | 10 ++-
> >  4 files changed, 51 insertions(+), 33 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index 0fcb94f7dbe5..ab87209c25d8 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -653,36 +653,44 @@ int drm_dp_downstream_max_clock(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE],
> >  EXPORT_SYMBOL(drm_dp_downstream_max_clock);
> >  
> >  /**
> > - * drm_dp_downstream_max_bpc() - extract branch device max
> > - *                               bits per component
> > - * @dpcd: DisplayPort configuration data
> > - * @port_cap: port capabilities
> > - *
> > - * See also:
> > - * drm_dp_read_downstream_info()
> > - * drm_dp_downstream_max_clock()
> > - *
> > - * Returns: Max bpc on success or 0 if max bpc not defined
> > - */
> > +  * drm_dp_downstream_max_bpc() - extract downstream facing port max
> > +  *                               bits per component
> > +  * @dpcd: DisplayPort configuration data
> > +  * @port_cap: downstream facing port capabilities
> > +  * @edid: EDID
> > +  *
> > +  * Returns max bpc on success or 0 if max bpc not defined
> > +  */
> >  int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > -			      const u8 port_cap[4])
> > +			      const u8 port_cap[4],
> > +			      const struct edid *edid)
> >  {
> > -	int type = port_cap[0] & DP_DS_PORT_TYPE_MASK;
> > -	bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> > -		DP_DETAILED_CAP_INFO_AVAILABLE;
> > -	int bpc;
> > -
> > -	if (!detailed_cap_info)
> 
> I don't think we can drop this check. There's a somewhat surprising blurb
> about downstream port caps in the DP 2.0 spec (section 5.3.3.1):
> 
>    In addition, the adapter shall set the Detailed Capabilities Info registers
>    (DPCD Addresses 00080h through 0008Fh) to show all the downstream types,
>    including DFP 0. Either one or four bytes are used, per DFP type
>    indication. Therefore, up to 16 (with 1-byte descriptor) or four (with 4-
>    byte descriptor) DFP capabilities can be stored.
> 
> I've never once actually seen a sink do this, but this does mean it's
> technically possible tthat if we don't check the detailed caps bit then we
> might end up reading another port's DFP type instead of max_bpc info. Note
> though that we can make the assumption the four byte version of the field is
> used for DP 1.4+

The check is now ...


> 
> > +	if (!drm_dp_is_branch(dpcd))
> >  		return 0;
> >  
> > -	switch (type) {
> > -	case DP_DS_PORT_TYPE_VGA:
> > -	case DP_DS_PORT_TYPE_DVI:
> > -	case DP_DS_PORT_TYPE_HDMI:
> > +	if (dpcd[DP_DPCD_REV] < 0x11) {
> > +		switch (dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> > DP_DWN_STRM_PORT_TYPE_MASK) {
> > +		case DP_DWN_STRM_PORT_TYPE_DP:
> > +			return 0;
> > +		default:
> > +			return 8;
> > +		}
> > +	}
> > +
> > +	switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
> > +	case DP_DS_PORT_TYPE_DP:
> > +		return 0;
> >  	case DP_DS_PORT_TYPE_DP_DUALMODE:
> > -		bpc = port_cap[2] & DP_DS_MAX_BPC_MASK;
> > +		if (is_edid_digital_input_dp(edid))
> > +			return 0;
> > +		fallthrough;
> > +	case DP_DS_PORT_TYPE_HDMI:
> > +	case DP_DS_PORT_TYPE_DVI:
> > +	case DP_DS_PORT_TYPE_VGA:
> > +		if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> > DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
> > +			return 8;

... here


> >  
> > -		switch (bpc) {
> > +		switch (port_cap[2] & DP_DS_MAX_BPC_MASK) {
> >  		case DP_DS_8BPC:
> >  			return 8;
> >  		case DP_DS_10BPC:
> > @@ -691,10 +699,12 @@ int drm_dp_downstream_max_bpc(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE],
> >  			return 12;
> >  		case DP_DS_16BPC:
> >  			return 16;
> > +		default:
> > +			return 8;
> >  		}
> > -		fallthrough;
> > +		break;
> >  	default:
> > -		return 0;
> > +		return 8;
> >  	}
> >  }
> >  EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
> > @@ -717,12 +727,15 @@ EXPORT_SYMBOL(drm_dp_downstream_id);
> >   * @m: pointer for debugfs file
> >   * @dpcd: DisplayPort configuration data
> >   * @port_cap: port capabilities
> > + * @edid: EDID
> >   * @aux: DisplayPort AUX channel
> >   *
> >   */
> >  void drm_dp_downstream_debug(struct seq_file *m,
> >  			     const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > -			     const u8 port_cap[4], struct drm_dp_aux *aux)
> > +			     const u8 port_cap[4],
> > +			     const struct edid *edid,
> > +			     struct drm_dp_aux *aux)
> >  {
> >  	bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> >  				 DP_DETAILED_CAP_INFO_AVAILABLE;
> > @@ -789,7 +802,7 @@ void drm_dp_downstream_debug(struct seq_file *m,
> >  				seq_printf(m, "\t\tMax TMDS clock: %d kHz\n",
> > clk);
> >  		}
> >  
> > -		bpc = drm_dp_downstream_max_bpc(dpcd, port_cap);
> > +		bpc = drm_dp_downstream_max_bpc(dpcd, port_cap, edid);
> >  
> >  		if (bpc > 0)
> >  			seq_printf(m, "\t\tMax bpc: %d\n", bpc);
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > index 53a0a3d9a22d..0bf31f9a8af5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > @@ -626,6 +626,7 @@ static void intel_dp_info(struct seq_file *m,
> >  {
> >  	struct intel_encoder *intel_encoder =
> > intel_attached_encoder(intel_connector);
> >  	struct intel_dp *intel_dp = enc_to_intel_dp(intel_encoder);
> > +	const struct drm_property_blob *edid = intel_connector-
> > >base.edid_blob_ptr;
> >  
> >  	seq_printf(m, "\tDPCD rev: %x\n", intel_dp->dpcd[DP_DPCD_REV]);
> >  	seq_printf(m, "\taudio support: %s\n", yesno(intel_dp->has_audio));
> > @@ -633,7 +634,7 @@ static void intel_dp_info(struct seq_file *m,
> >  		intel_panel_info(m, &intel_connector->panel);
> >  
> >  	drm_dp_downstream_debug(m, intel_dp->dpcd, intel_dp->downstream_ports,
> > -				&intel_dp->aux);
> > +				edid ? edid->data : NULL, &intel_dp->aux);
> >  }
> >  
> >  static void intel_dp_mst_info(struct seq_file *m,
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 2c8e82d97a34..c73b3efd84e0 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -6071,7 +6071,7 @@ intel_dp_set_edid(struct intel_dp *intel_dp)
> >  
> >  	intel_dp->dfp.max_bpc =
> >  		drm_dp_downstream_max_bpc(intel_dp->dpcd,
> > -					  intel_dp->downstream_ports);
> > +					  intel_dp->downstream_ports, edid);
> >  
> >  	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s] DFP max bpc %d\n",
> >  		    connector->base.base.id, connector->base.name,
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index 4f946826dfce..6218de1294c1 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -1646,10 +1646,14 @@ bool drm_dp_downstream_is_tmds(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE],
> >  int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> >  				const u8 port_cap[4]);
> >  int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > -			      const u8 port_cap[4]);
> > +			      const u8 port_cap[4],
> > +			      const struct edid *edid);
> >  int drm_dp_downstream_id(struct drm_dp_aux *aux, char id[6]);
> > -void drm_dp_downstream_debug(struct seq_file *m, const u8
> > dpcd[DP_RECEIVER_CAP_SIZE],
> > -			     const u8 port_cap[4], struct drm_dp_aux *aux);
> > +void drm_dp_downstream_debug(struct seq_file *m,
> > +			     const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > +			     const u8 port_cap[4],
> > +			     const struct edid *edid,
> > +			     struct drm_dp_aux *aux);
> >  enum drm_mode_subconnector
> >  drm_dp_subconnector_type(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> >  			 const u8 port_cap[4]);
> -- 
> Cheers,
> 	Lyude Paul (she/her)
> 	Software Engineer at Red Hat

-- 
Ville Syrjälä
Intel
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel