[PATCH v4 05/11] drm: Helper to read max bits per component

[Mika Kahola]

On Thu, 2016-06-09 at 11:02 +0300, Ville Syrjälä wrote:
> On Mon, Jun 06, 2016 at 04:29:07PM +0300, Mika Kahola wrote:
> > Helper routine to read out maximum supported bits per
> > component for DisplayPort legay converters.
> > 
> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c | 31 +++++++++++++++++++++++++++++++
> >  include/drm/drm_dp_helper.h     |  2 ++
> >  2 files changed, 33 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > index 18b72eb..bac0ccc 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -507,6 +507,37 @@ 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
> > + *
> > + * Returns max bpc on success or negative error code on failure
> > + */
> > +int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > +                              const u8 port_cap[4])
> > +{
> > +	int type = drm_dp_downstream_type(dpcd, port_cap);
> > +	bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> > +		DP_DETAILED_CAP_INFO_AVAILABLE;
> > +
> > +	if (detailed_cap_info) {
> 
> Early return again.
> 
> > +		if (type != DP_DS_PORT_TYPE_WIRELESS) {
> 
> switch() again.
> 
> > +			int tmp;
> > +			tmp = port_cap[2] & DP_DS_VGA_MAX_BPC_MASK;
> 
> Should drop the "VGA" from that stuff since it applies to more than
> that.

Agreed. Maybe we could rename it as DP_DS_MAX_BPC_MASK instead.

> 
> > +
> > +			if (tmp == 0)
> > +				return 8;
> > +			else
> > +				return 8 + (1<<tmp);
> 
> switch() with each case would be less magicy.
> 
> > +		}
> > +	}
> > +
> > +	return -EINVAL;
> 
> Again I think I'd just use 0 here.
> 
> > +}
> > +EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
> > +
> >  /*
> >   * I2C-over-AUX implementation
> >   */
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index c3324d3..d4abc38 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -812,6 +812,8 @@ int drm_dp_downstream_port_cap(struct drm_dp_aux *aux,
> >  int drm_dp_downstream_type(const u8 dpcd[DP_RECEIVER_CAP_SIZE], const u8 port_cap[4]);
> >  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]);
> >  
> >  int drm_dp_aux_register(struct drm_dp_aux *aux);
> >  void drm_dp_aux_unregister(struct drm_dp_aux *aux);
> > -- 
> > 1.9.1
> 

-- 
Mika Kahola - Intel OTC