Re: [PATCH v8 04/10] drm: bridge: dw_mipi_dsi: allow bridge daisy chaining

[Adrian Ratiu]

On Wed, 03 Jun 2020, Laurent Pinchart 
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> Hi Adrian, 

Hi Laurent,

> Thank you for the patch. 
>
> On Mon, Apr 27, 2020 at 11:19:46AM +0300, Adrian Ratiu wrote: 
> > Up until now the assumption was that the synopsis dsi bridge 
> > will directly connect to an encoder provided by the platform 
> > driver, but the current practice for drivers is to leave the 
> > encoder empty via the simple encoder API and add their logic to 
> > their own drm_bridge.   Thus we need an ablility to connect the 
> > DSI bridge to another bridge provided by the platform driver, 
> > so we extend the dw_mipi_dsi bind() API with a new "previous 
> > bridge" arg instead of just hardcoding NULL.   Cc: Laurent 
> > Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> Signed-off-by: 
> > Adrian Ratiu <adrian.ratiu@xxxxxxxxxxxxx> --- New in v8.  --- 
> >  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c   | 6 ++++-- 
> >  drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c | 2 +- 
> >  include/drm/bridge/dw_mipi_dsi.h                | 5 ++++- 3 
> >  files changed, 9 insertions(+), 4 deletions(-) 
> >  diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c 
> > b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c index 
> > 16fd87055e7b7..140ff40fa1b62 100644 --- 
> > a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c +++ 
> > b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c @@ -1456,11 
> > +1456,13 @@ EXPORT_SYMBOL_GPL(dw_mipi_dsi_remove); 
> >  /* 
> >   * Bind/unbind API, used from platforms based on the component 
> >   framework.  */ 
> > -int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi, struct 
> > drm_encoder *encoder) +int dw_mipi_dsi_bind(struct dw_mipi_dsi 
> > *dsi, +		     struct drm_encoder *encoder, + 
> > struct drm_bridge *prev_bridge) 
> >  { int ret;  
> > -	ret = drm_bridge_attach(encoder, &dsi->bridge, NULL, 0); + 
> > ret = drm_bridge_attach(encoder, &dsi->bridge, prev_bridge, 0); 
>
> Please note that chaining of bridges doesn't work well if 
> multiple bridges in the chain try to create a connector. This is 
> why a DRM_BRIDGE_ATTACH_NO_CONNECTOR flag has been added, with a 
> helper to create a connector for a chain of bridges 
> (drm_bridge_connector_init()).  This won't play well with the 
> component framework. I would recommend using the 
> of_drm_find_bridge() instead in the rockchip driver, and 
> deprecating dw_mipi_dsi_bind(). 

Thank you for this insight, indeed the bridge dw_mipi_dsi_bind() 
is clunky and we're making it even more so by possibly 
re-inventing drm_bridge_connector_init() with it in a way which 
can't work (well it does work but can lead to those nasty 
multiple-encoder corner-cases you mention).

I'll address this before posting v9, to try to move to 
of_drm_find_bridge() and remove dw_mipi_dsi_bind().

> >  	if (ret) {
> >  		DRM_ERROR("Failed to initialize bridge with drm\n");
> >  		return ret;
> > diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> > index 3feff0c45b3f7..83ef43be78135 100644
> > --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> > +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> > @@ -929,7 +929,7 @@ static int dw_mipi_dsi_rockchip_bind(struct device *dev,
> >  		return ret;
> >  	}
> >  
> > -	ret = dw_mipi_dsi_bind(dsi->dmd, &dsi->encoder);
> > +	ret = dw_mipi_dsi_bind(dsi->dmd, &dsi->encoder, NULL);
> >  	if (ret) {
> >  		DRM_DEV_ERROR(dev, "Failed to bind: %d\n", ret);
> >  		return ret;
> > diff --git a/include/drm/bridge/dw_mipi_dsi.h b/include/drm/bridge/dw_mipi_dsi.h
> > index b0e390b3288e8..699b3531f5b36 100644
> > --- a/include/drm/bridge/dw_mipi_dsi.h
> > +++ b/include/drm/bridge/dw_mipi_dsi.h
> > @@ -14,6 +14,7 @@
> >  #include <drm/drm_modes.h>
> >  
> >  struct drm_display_mode;
> > +struct drm_bridge;
> >  struct drm_encoder;
> >  struct dw_mipi_dsi;
> >  struct mipi_dsi_device;
> > @@ -62,7 +63,9 @@ struct dw_mipi_dsi *dw_mipi_dsi_probe(struct platform_device *pdev,
> >  				      const struct dw_mipi_dsi_plat_data
> >  				      *plat_data);
> >  void dw_mipi_dsi_remove(struct dw_mipi_dsi *dsi);
> > -int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi, struct drm_encoder *encoder);
> > +int dw_mipi_dsi_bind(struct dw_mipi_dsi *dsi,
> > +		     struct drm_encoder *encoder,
> > +		     struct drm_bridge *prev_bridge);
> >  void dw_mipi_dsi_unbind(struct dw_mipi_dsi *dsi);
> >  void dw_mipi_dsi_set_slave(struct dw_mipi_dsi *dsi, struct dw_mipi_dsi *slave);
> >  
>
> --
> Regards,
>
> Laurent Pinchart