[PATCH v4 1/2] drm/dp: Store the drm_connector device pointer on the helper.

[Lukas Wunner]

Hi Daniel,

On Tue, Sep 29, 2015 at 05:04:03PM +0200, Daniel Vetter wrote:
> On Tue, Sep 29, 2015 at 02:49:20PM +0200, Lukas Wunner wrote:
> > On Mon, Sep 28, 2015 at 04:45:35PM -0700, Rafael Antognolli wrote:
> > > This is useful to determine which connector owns this AUX channel.
> > 
> > WTF? I posted a patch in August which does exactly that:
> > http://lists.freedesktop.org/archives/dri-devel/2015-August/088172.html
> > 
> > Can also be pulled in from this git repo:
> > https://github.com/l1k/linux/commit/b78b38d53fc0fc4fa0f6acf699b0fcad56ec1fe6
> > 
> > My patch has the advantage that it updates all the drivers which use
> > drm_dp_aux to fill that attribute. Yours only updates i915.
> > 
> > Daniel Vetter criticized storing a drm_connector pointer in drm_dp_aux,
> > quote:
> > 
> > "That will also clear up the confusion with drm_dp_aux, adding a
> > drm_connector there feels wrong since not every dp_aux line has a
> > connector (e.g. for dp mst). If we can lift this relation out into drivers
> > (where this is known) that seems cleaner."
> > 
> > So now Intel itself does precisely what Daniel criticized? Confusing!
> > 
> > Source:
> > http://lists.freedesktop.org/archives/dri-devel/2015-August/089108.html
> 
> Critism is still valid, and thinking about this again a cleaner solution
> would be to just have a correct parent/child relationship in the device
> hirarchy. I.e. add a struct device *parent to the aux channel structure
> which should point to the right connector.

We already have that:

struct drm_dp_aux {
	const char *name;
	struct i2c_adapter ddc;
	struct device *dev;				<-----------
	struct mutex hw_mutex;
	ssize_t (*transfer)(struct drm_dp_aux *aux,
			    struct drm_dp_aux_msg *msg);
	unsigned i2c_nack_count, i2c_defer_count;
};

What Rafael is struggling with is that you cannot unambiguously
get from drm_dp_aux->dev to the drm_connector. (The drm_device
may have multiple drm_connectors with type
DRM_MODE_CONNECTOR_DisplayPort.)

> 
> Thanks for pointing out that I missed properly delayering this.
> -Daniel
> 
> > 
> > 
> > Best regards,
> > 
> > Lukas
> > 
> > 
> > > 
> > > Signed-off-by: Rafael Antognolli <rafael.antognolli at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 1 +
> > >  include/drm/drm_dp_helper.h     | 1 +
> > >  2 files changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 77f7330..f90439d 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -1079,6 +1079,7 @@ intel_dp_aux_init(struct intel_dp *intel_dp, struct intel_connector *connector)
> > >  
> > >  	intel_dp->aux.name = name;
> > >  	intel_dp->aux.dev = dev->dev;
> > > +	intel_dp->aux.connector = connector->base.kdev;
> > >  	intel_dp->aux.transfer = intel_dp_aux_transfer;
> > >  
> > >  	DRM_DEBUG_KMS("registering %s bus for %s\n", name,
> > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > > index 9ec4716..e009b5d 100644
> > > --- a/include/drm/drm_dp_helper.h
> > > +++ b/include/drm/drm_dp_helper.h
> > > @@ -702,6 +702,7 @@ struct drm_dp_aux {
> > >  	const char *name;
> > >  	struct i2c_adapter ddc;
> > >  	struct device *dev;
> > > +	struct device *connector;
> > >  	struct mutex hw_mutex;
> > >  	ssize_t (*transfer)(struct drm_dp_aux *aux,
> > >  			    struct drm_dp_aux_msg *msg);
> > > -- 
> > > 2.4.3
> > > 
> > > _______________________________________________
> > > dri-devel mailing list
> > > dri-devel at lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch