Re: [PATCH 2/3] drm/dp_mst: Fix the DDC I2C device registration of an MST port

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Wed, Jun 10, 2020 at 01:09:36PM +0300, Imre Deak wrote:
> On Wed, Jun 10, 2020 at 11:03:04AM +0300, Lisovskiy, Stanislav wrote:
> > On Mon, Jun 08, 2020 at 12:25:21AM +0300, Imre Deak wrote:
> > > During the initial MST probing an MST port's I2C device will be
> > > registered using the kdev of the DRM device as a parent. Later after MST
> > > Connection Status Notifications this I2C device will be re-registered
> > > with the kdev of the port's connector. This will also move
> > > inconsistently the I2C device's sysfs entry from the DRM device's sysfs
> > > dir to the connector's dir.
> > > 
> > > Fix the above by keeping the DRM kdev as the parent of the I2C device.
> > > 
> > > Ideally the connector's kdev would be used as a parent, similarly to
> > > non-MST connectors, however that needs some more refactoring to ensure
> > > the connector's kdev is already available early enough. So keep the
> > > existing (initial) behavior for now.
> > > 
> > > Cc: <stable@vger.kernel.org>
> > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_dp_mst_topology.c | 28 +++++++++++++++------------
> > >  1 file changed, 16 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 02c800b8199f..083255c33ee0 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -88,8 +88,8 @@ static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
> > >  static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
> > >  				 u8 *guid);
> > >  
> > > -static int drm_dp_mst_register_i2c_bus(struct drm_dp_aux *aux);
> > > -static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux);
> > > +static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port);
> > > +static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port);
> > >  static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);
> > >  
> > >  #define DBG_PREFIX "[dp_mst]"
> > > @@ -1993,7 +1993,7 @@ drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
> > >  			}
> > >  
> > >  			/* remove i2c over sideband */
> > > -			drm_dp_mst_unregister_i2c_bus(&port->aux);
> > > +			drm_dp_mst_unregister_i2c_bus(port);
> > >  		} else {
> > >  			mutex_lock(&mgr->lock);
> > >  			drm_dp_mst_topology_put_mstb(port->mstb);
> > > @@ -2008,7 +2008,7 @@ drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
> > >  	if (port->pdt != DP_PEER_DEVICE_NONE) {
> > >  		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
> > >  			/* add i2c over sideband */
> > > -			ret = drm_dp_mst_register_i2c_bus(&port->aux);
> > > +			ret = drm_dp_mst_register_i2c_bus(port);
> > >  		} else {
> > >  			lct = drm_dp_calculate_rad(port, rad);
> > >  			mstb = drm_dp_add_mst_branch_device(lct, rad);
> > > @@ -5375,22 +5375,26 @@ static const struct i2c_algorithm drm_dp_mst_i2c_algo = {
> > >  
> > >  /**
> > >   * drm_dp_mst_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
> > > - * @aux: DisplayPort AUX channel
> > > + * @port: The port to add the I2C bus on
> > >   *
> > >   * Returns 0 on success or a negative error code on failure.
> > >   */
> > > -static int drm_dp_mst_register_i2c_bus(struct drm_dp_aux *aux)
> > > +static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
> > >  {
> > > +	struct drm_dp_aux *aux = &port->aux;
> > > +	struct device *parent_dev = port->mgr->dev->dev;
> > > +
> > 
> > So are we sure that this will always give us thr kdev of the drm device?
> > I mean could there be more complex hierarchy? Just wondering if there is 
> > a way to get drm device kdev in a more explicit way.
> 
> There is a single mgr per DRM driver (kdev) and port objects created by
> a given DRM driver will stay owned by the same DRM driver. So the
> kdev->port association is static.

Ok, thanks for clarification. lgtm then.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> 
> > >  	aux->ddc.algo = &drm_dp_mst_i2c_algo;
> > >  	aux->ddc.algo_data = aux;
> > >  	aux->ddc.retries = 3;
> > >  
> > >  	aux->ddc.class = I2C_CLASS_DDC;
> > >  	aux->ddc.owner = THIS_MODULE;
> > > -	aux->ddc.dev.parent = aux->dev;
> > > -	aux->ddc.dev.of_node = aux->dev->of_node;
> > > +	/* FIXME: set the kdev of the port's connector as parent */
> > > +	aux->ddc.dev.parent = parent_dev;
> > > +	aux->ddc.dev.of_node = parent_dev->of_node;
> > >  
> > > -	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
> > > +	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev),
> > >  		sizeof(aux->ddc.name));
> > >  
> > >  	return i2c_add_adapter(&aux->ddc);
> > > @@ -5398,11 +5402,11 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_aux *aux)
> > >  
> > >  /**
> > >   * drm_dp_mst_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
> > > - * @aux: DisplayPort AUX channel
> > > + * @port: The port to remove the I2C bus from
> > >   */
> > > -static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux)
> > > +static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port)
> > >  {
> > > -	i2c_del_adapter(&aux->ddc);
> > > +	i2c_del_adapter(&port->aux.ddc);
> > >  }
> > >  
> > >  /**
> > > -- 
> > > 2.23.1
> > > 
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