[alsa-devel] [PATCH 12/15] drm/edid: Add API to help find connection type

[Subhransu S. Prusty]

On Thu, Dec 03, 2015 at 12:21:42PM +0100, Thierry Reding wrote:
> On Thu, Dec 03, 2015 at 01:09:16PM +0200, Jani Nikula wrote:
> > On Thu, 03 Dec 2015, "Subhransu S. Prusty" <subhransu.s.prusty at intel.com> wrote:
> > > On Wed, Dec 02, 2015 at 06:07:01PM +0100, Thierry Reding wrote:
> > >> On Wed, Dec 02, 2015 at 11:53:02AM +0200, Jani Nikula wrote:
> > >> > On Tue, 01 Dec 2015, "Subhransu S. Prusty" <subhransu.s.prusty at intel.com> wrote:
> > >> > > To fill the audio infoframe it is required to identify the connection type
> > >> > > as DP or HDMI. So parse the required bits in ELD to find the connection
> > >> > > type.
> > >> > >
> > >> > > Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty at intel.com>
> > >> > > Signed-off-by: Vinod Koul <vinod.koul at intel.com>
> > >> > > Cc: David Airlie <airlied at linux.ie>
> > >> > > Cc: dri-devel at lists.freedesktop.org
> > >> > > Cc: Daniel Vetter <daniel.vetter at intel.com>
> > >> > > ---
> > >> > >  include/drm/drm_edid.h | 10 ++++++++++
> > >> > >  1 file changed, 10 insertions(+)
> > >> > >
> > >> > > diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> > >> > > index 2af9769..c7595a5 100644
> > >> > > --- a/include/drm/drm_edid.h
> > >> > > +++ b/include/drm/drm_edid.h
> > >> > > @@ -403,6 +403,16 @@ static inline int drm_eld_size(const uint8_t *eld)
> > >> > >  	return DRM_ELD_HEADER_BLOCK_SIZE + eld[DRM_ELD_BASELINE_ELD_LEN] * 4;
> > >> > >  }
> > >> > >  
> > >> > > +/**
> > >> > > + * drm_eld_get_conn_type - Get device type hdmi/dp connected
> > >> > > + * @eld: pointer to an eld memory structure
> > >> > > + */
> > >> > > +static inline int drm_eld_get_conn_type(const uint8_t *eld)
> > >> > > +{
> > >> > > +	return (eld[DRM_ELD_SAD_COUNT_CONN_TYPE] & DRM_ELD_CONN_TYPE_MASK) >>
> > >> > > +		DRM_ELD_CONN_TYPE_SHIFT;
> > >> > > +}
> > >> > 
> > >> > I'm not sure how much this helps when the caller still needs to
> > >> > magically know what the return value means...  Indeed the next patch
> > >> > with /* 0 is hdmi and 1 is DP */ and "conn_type == 0" is a bit ugly.
> > >> > 
> > >> > How about just not shifting the return value, and using
> > >> > DRM_ELD_CONN_TYPE_HDMI and DRM_ELD_CONN_TYPE_DP in the caller? Bonus
> > >> > points for referencing those in the kernel-doc above.
> > >> 
> > >> We already have a similar function for detecting HDMI vs. DVI (see the
> > >> drm_detect_hdmi_monitor()), so perhaps adhering to that convention might
> > >> be preferable. This could be:
> > >> 
> > >> 	static inline bool drm_eld_detect_dp(const u8 *eld)
> > >> 	{
> > >> 		u8 type = eld[DRM_ELD_SAD_COUNT_CONN_TYPE] & DRM_ELD_CONN_TYPE_MASK;
> > >> 
> > >> 		return type == DRM_ELD_CONN_TYPE_DP;
> > >> 	}
> > >
> > > With this approach it needs two APIs to be added for HDMI or DP
> > > detection. So I prefer what Jani suggested and caller compares
> > > whether it is HDMI/DP connection type. Will updae the kernel doc
> > > for the same as well.
> > 
> > I presume Thierry means you'd assume HDMI if drm_eld_detect_dp() returns
> > false.
> 
> Yes, that's what I was implying. This is probably highly subjective, but
> I personally find boolean return values much easier to deal with because
> of the limited set of values. With drm_eld_get_conn_type() you'd need to
> explicitly check == DRM_ELD_CONN_TYPE_HDMI and == DRM_ELD_CONN_TYPE_DP
> and then still have special code to reject all other values. Unless of

I don't know what does the second bit mean in the connection type. So was
just planning to reject anything other that DP/HDMI. If that bit doesn't
carry any information, then yes I would also prefer returning a boolean.

> course if you consider != DRM_ELD_CONN_TYPE_DP as being HDMI, in which
> case a boolean is much more concise.
> 
> But like I said, this is just my opinion, and I don't feel strongly
> enough to object to the current patch.
> 
> Thierry



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