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

From: Thierry Reding <thierry.reding@gmail.com>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: alsa-devel@alsa-project.org, patches.audio@intel.com,
	lgirdwood@gmail.com, dri-devel@lists.freedesktop.org,
	Vinod Koul <vinod.koul@intel.com>,
	broonie@kernel.org, Daniel Vetter <daniel.vetter@intel.com>,
	"Subhransu S. Prusty" <subhransu.s.prusty@intel.com>
Subject: Re: [PATCH 12/15] drm/edid: Add API to help find connection type
Date: Wed, 2 Dec 2015 18:07:01 +0100	[thread overview]
Message-ID: <20151202170701.GB14019@ulmo> (raw)
In-Reply-To: <87y4dd2n41.fsf@intel.com>

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On Wed, Dec 02, 2015 at 11:53:02AM +0200, Jani Nikula wrote:
> On Tue, 01 Dec 2015, "Subhransu S. Prusty" <subhransu.s.prusty@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@intel.com>
> > Signed-off-by: Vinod Koul <vinod.koul@intel.com>
> > Cc: David Airlie <airlied@linux.ie>
> > Cc: dri-devel@lists.freedesktop.org
> > Cc: Daniel Vetter <daniel.vetter@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;
	}

Thierry

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