[PATCH v7 1/5] drm: Read DP branch device HW revision

[Mika Kahola]

On Thu, 2016-08-11 at 10:10 +0300, Ville Syrjälä wrote:
> On Mon, Aug 08, 2016 at 04:00:26PM +0300, Mika Kahola wrote:
> > HW revision is mandatory field for DisplayPort branch
> > devices. This is defined in DPCD register field 0x509.
> 
> But what do we want to do with it? Me, I don't see a point in parsing a
> bunch of stuff from the DPCD unless there's a real use case for it.
> /dev/drm_dp_aux will provide all the debug aid we need if we need to
> check random pieces of data from the DPCD, so even exposing this sort
> of stuff via debugfs is IMO pretty pointless.
> 
> If there's a good reason for a debug print, then I think we could parse
> something and dump it out so that it's always in the dmesg. But so far
> I'm not aware of any bug that would have required to deal with different
> hw revisions of things and whatnot.
> 
Digging up the HW and SW revisions are just for debugging purposes. My
idea here was that it would be handy if this information would be
available if we face a problem let's say with VGA dongle for example. It
is true that at the moment we don't have a single bug that would require
HW/SW revision information but maybe in the future we have one.

So, if we don't want to have this stuff in drm_dp_helpers and/or debugfs
I could make a change and print this info on dmesg when DP branch device
is plugged in.

Cheers,
Mika

> > 
> > v2: move drm_dp_ds_revision structure to be part of
> >     drm_dp_link structure (Daniel)
> > 
> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c  | 27 +++++++++++++++++++++++++++
> >  drivers/gpu/drm/i915/intel_drv.h |  1 +
> >  include/drm/drm_dp_helper.h      |  9 +++++++++
> >  3 files changed, 37 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > index 75b2873..5fecdc1 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -514,6 +514,33 @@ int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> >  EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
> >  
> >  /**
> > + * drm_dp_downstream_hw_rev() - read DP branch device HW revision
> > + * @aux: DisplayPort AUX channel
> > + *
> > + * Returns 0 on succes or negative error code on failure
> > + */
> > +int drm_dp_downstream_hw_rev(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > +			     struct drm_dp_aux *aux, struct drm_dp_link *link)
> > +{
> > +	uint8_t tmp;
> > +	int err;
> > +
> > +	if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
> > +		return -EINVAL;
> > +
> > +	err = drm_dp_dpcd_read(aux, DP_BRANCH_HW_REV, &tmp, 1);
> > +
> > +	if (err < 0)
> > +		return err;
> > +
> > +	link->ds_hw_rev.major = (tmp & 0xf0) >> 4;
> > +	link->ds_hw_rev.minor = tmp & 0xf;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_downstream_hw_rev);
> > +
> > +/**
> >   * drm_dp_downstream_id() - identify branch device
> >   * @aux: DisplayPort AUX channel
> >   *
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index e74d851..a6eccf5 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -865,6 +865,7 @@ struct intel_dp {
> >  	uint8_t num_sink_rates;
> >  	int sink_rates[DP_MAX_SUPPORTED_RATES];
> >  	struct drm_dp_aux aux;
> > +	struct drm_dp_link link;
> >  	uint8_t train_set[4];
> >  	int panel_power_up_delay;
> >  	int panel_power_down_delay;
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index 8e1fe58..1127948 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -446,6 +446,7 @@
> >  #define DP_SINK_OUI			    0x400
> >  #define DP_BRANCH_OUI			    0x500
> >  #define DP_BRANCH_ID                        0x503
> > +#define DP_BRANCH_HW_REV                    0x509
> >  
> >  #define DP_SET_POWER                        0x600
> >  # define DP_SET_POWER_D0                    0x1
> > @@ -803,11 +804,17 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
> >   */
> >  #define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0)
> >  
> > +struct drm_dp_ds_revision {
> > +	int major;
> > +	int minor;
> > +};
> > +
> >  struct drm_dp_link {
> >  	unsigned char revision;
> >  	unsigned int rate;
> >  	unsigned int num_lanes;
> >  	unsigned long capabilities;
> > +	struct drm_dp_ds_revision ds_hw_rev;
> >  };
> >  
> >  int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
> > @@ -819,6 +826,8 @@ int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> >  int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> >  			      const u8 port_cap[4]);
> >  int drm_dp_downstream_id(struct drm_dp_aux *aux, char id[6]);
> > +int drm_dp_downstream_hw_rev(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > +			     struct drm_dp_aux *aux, struct drm_dp_link *link);
> >  
> >  void drm_dp_aux_init(struct drm_dp_aux *aux);
> >  int drm_dp_aux_register(struct drm_dp_aux *aux);
> > -- 
> > 1.9.1
>