Re: [PATCH 01/20] drm/bridge: add dsi_lp11_notify mechanism

["Michael Walle" <mwalle@kernel.org>]

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[+ Marek ]

Hi Dmitry,

> > > Some bridges have very strict power-up reqirements. In this case, the
> > > Toshiba TC358775. The reset has to be deasserted while *both* the DSI
> > > clock and DSI data lanes are in LP-11 mode. After the reset is relased,
> > > the bridge needs the DSI clock to actually be able to process I2C
> > > access. This access will configure the DSI side of the bridge during
> > > which the DSI data lanes have to be in LP-11 mode.
> > 
> > Apparently this is an issue for a lot of DSI bridges. But enabling LP-11 for
> > a bridge is impossible with current documentation [1], which states "A DSI
> > host should keep the PHY powered down until the pre_enable operation is
> > called."
> > Additionally tc358767/tc9595 (DSI-DP bridge) needs LP-11 for AUX channel
> > access to even get EDID. This is a requirement before pre_enable would
> > even be possible.
> > 
> > So some changes to the current flow are needed. But I am not so sure
> > about LP-11 notification. IMHO a device request to the DSI host to
> > enable LP-11 seems more sensible.
>
> Granted that there can be several DSI devices sharing the DSI bus (aka
> split-link), I was toying with the idea of making the DSI host call
> attached DSI devices when the transition happens.

So almost the same, as this patch?

> I don't have a fully working PoC and I probably won't have it ready til
> the end of May because of the lack of time and different local
> priorities.

Any news regarding this?

-michael

> > Best regards,
> > Alexander
> > 
> > [1] https://www.kernel.org/doc/html/latest/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation
> > 
> > > After everything is
> > > configured the video stream can finally be enabled.
> > > 
> > > This means:
> > >  (1) The bridge has to be configured completely in .pre_enable() op
> > >      (with the clock turned on and data lanes in LP-11 mode, thus
> > >      .pre_enable_prev_first has to be set).
> > >  (2) The bridge will enable its output in the .enable() op
> > >  (3) There must be some mechanism before (1) where the bridge can
> > >      release its reset while the clock lane is still in LP-11 mode.
> > > 
> > > Unfortunately, (3) is crucial for a correct operation of the bridge.
> > > To satisfy this requriment, introduce a new callback .dsi_lp11_notify()
> > > which will be called by the DSI host driver.
> > > 
> > > Signed-off-by: Michael Walle <mwalle@kernel.org>
> > > ---
> > >  drivers/gpu/drm/drm_bridge.c | 16 ++++++++++++++++
> > >  include/drm/drm_bridge.h     | 12 ++++++++++++
> > >  2 files changed, 28 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > > index 28abe9aa99ca..98cd6558aecb 100644
> > > --- a/drivers/gpu/drm/drm_bridge.c
> > > +++ b/drivers/gpu/drm/drm_bridge.c
> > > @@ -1339,6 +1339,22 @@ void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > >  }
> > >  EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> > >  
> > > +/**
> > > + * drm_bridge_dsi_lp11_notify - notify clock/data lanes LP-11 mode
> > > + * @bridge: bridge control structure
> > > + *
> > > + * DSI host drivers shall call this function while the clock and data lanes
> > > + * are still in LP-11 mode.
> > > + *
> > > + * This function shall be called in a context that can sleep.
> > > + */
> > > +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge)
> > > +{
> > > +	if (bridge->funcs->dsi_lp11_notify)
> > > +		bridge->funcs->dsi_lp11_notify(bridge);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_dsi_lp11_notify);
> > > +
> > >  #ifdef CONFIG_OF
> > >  /**
> > >   * of_drm_find_bridge - find the bridge corresponding to the device node in
> > > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > > index 4baca0d9107b..4ef61274e0a8 100644
> > > --- a/include/drm/drm_bridge.h
> > > +++ b/include/drm/drm_bridge.h
> > > @@ -630,6 +630,17 @@ struct drm_bridge_funcs {
> > >  	 */
> > >  	void (*hpd_disable)(struct drm_bridge *bridge);
> > >  
> > > +	/**
> > > +	 * dsi_lp11_notify:
> > > +	 *
> > > +	 * Will be called by the DSI host driver while both the DSI clock
> > > +	 * lane as well as the DSI data lanes are in LP-11 mode. Some bridges
> > > +	 * need this state while releasing the reset, for example.
> > > +	 * Not all DSI host drivers will support this. Therefore, the DSI
> > > +	 * bridge driver must not rely on this op to be called.
> > > +	 */
> > > +	void (*dsi_lp11_notify)(struct drm_bridge *bridge);
> > > +
> > >  	/**
> > >  	 * @debugfs_init:
> > >  	 *
> > > @@ -898,6 +909,7 @@ void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > >  void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> > >  void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > >  			   enum drm_connector_status status);
> > > +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge);
> > >  
> > >  #ifdef CONFIG_DRM_PANEL_BRIDGE
> > >  bool drm_bridge_is_panel(const struct drm_bridge *bridge);
> > > 
> > > 
> > 
> > 
> > -- 
> > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
> > Amtsgericht München, HRB 105018
> > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
> > http://www.tq-group.com/
> > 
> > 


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