linux-kernel - Re: [PATCH v3 16/17] platform/chrome: cros_ec

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Message-ID: <CAE-0n50Tuxp0WjFoTx+_i1L4cSOajSNHWPh32PPoXvskJByJJg@mail.gmail.com>
Date: Fri, 23 Aug 2024 13:44:41 -0700
From: Stephen Boyd <swboyd@...omium.org>
To: Tzung-Bi Shih <tzungbi@...nel.org>
Cc: chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	patches@...ts.linux.dev, devicetree@...r.kernel.org, 
	Douglas Anderson <dianders@...omium.org>, Pin-yen Lin <treapking@...omium.org>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Benson Leung <bleung@...omium.org>, 
	Conor Dooley <conor+dt@...nel.org>, Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...il.com>, 
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, dri-devel@...ts.freedesktop.org, 
	Guenter Roeck <groeck@...omium.org>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Jonas Karlman <jonas@...boo.se>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Lee Jones <lee@...nel.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Prashant Malani <pmalani@...omium.org>, 
	Robert Foss <rfoss@...nel.org>, Rob Herring <robh+dt@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Alexandre Belloni <alexandre.belloni@...tlin.com>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Daniel Scally <djrscally@...il.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Ivan Orlov <ivan.orlov0322@...il.com>, 
	linux-acpi@...r.kernel.org, linux-usb@...r.kernel.org, 
	Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Vinod Koul <vkoul@...nel.org>
Subject: Re: [PATCH v3 16/17] platform/chrome: cros_ec_typec: Support DP muxing

Quoting Tzung-Bi Shih (2024-08-22 07:37:05)
> On Mon, Aug 19, 2024 at 03:38:30PM -0700, Stephen Boyd wrote:
> > @@ -671,6 +674,20 @@ static int cros_typec_configure_mux(struct cros_typec_data *typec, int port_num,
> >       if (port->mux_flags == resp.flags && port->role == pd_ctrl->role)
> >               return 0;
> >
> > +     dp_enabled = resp.flags & USB_PD_MUX_DP_ENABLED;
> > +     hpd_asserted = resp.flags & USB_PD_MUX_HPD_LVL;
> > +     /*
> > +      * Assume the first port to have HPD asserted is the one muxed to DP
> > +      * (i.e. active_port). When there's only one port this delays setting
> > +      * the active_port until HPD is asserted, but before that the
> > +      * drm_connector looks disconnected so active_port doesn't need to be
> > +      * set.
> > +      */
> > +     if (dp_bridge && hpd_asserted && !dp_bridge->active_port)
> > +             dp_bridge->active_port = port;
> > +
> > +     is_active_port = !dp_bridge || dp_bridge->active_port == port;
>
> Why `!dp_bridge`?  When will `dp_bridge` be NULL?

I'll add a comment.

'dp_bridge' is NULL when this driver is running on non-DT platforms,
i.e. ACPI, or there isn't a graph/ports node for this device. The latter
could happen if there's some AP controlled piece of hardware that is a
typec switch, connected directly to a usb-c-connector. This is the case
on Kukui where we send the DP lanes directly to the usb-c-connector.