linux-kernel - Re: [PATCH v2 01/28] drm: Introduce drm_bridge

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Date:   Thu, 5 Dec 2019 14:40:22 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Mihail Atanassov <Mihail.Atanassov@....com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        nd <nd@....com>
Subject: Re: [PATCH v2 01/28] drm: Introduce drm_bridge_init()

Hi Mihail,

Thank you for the patch.

On Wed, Dec 04, 2019 at 11:48:02AM +0000, Mihail Atanassov wrote:
> A simple convenience function to initialize the struct drm_bridge. The
> goal is to standardize initialization for any bridge registered with
> drm_bridge_add() so that we can later add device links for consumers of
> those bridges.
> 
> v2:
>  - s/WARN_ON(!funcs)/WARN_ON(!funcs || !dev)/ as suggested by Daniel
>  - expand on some kerneldoc comments as suggested by Daniel
>  - update commit message as suggested by Daniel
> 
> Signed-off-by: Mihail Atanassov <mihail.atanassov@....com>
> ---
>  drivers/gpu/drm/drm_bridge.c | 34 +++++++++++++++++++++++++++++++++-
>  include/drm/drm_bridge.h     | 15 ++++++++++++++-
>  2 files changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index cba537c99e43..50e1c1b46e20 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -64,7 +64,10 @@ static DEFINE_MUTEX(bridge_lock);
>  static LIST_HEAD(bridge_list);
>  
>  /**
> - * drm_bridge_add - add the given bridge to the global bridge list
> + * drm_bridge_add - add the given bridge to the global bridge list.

You add a final period here and in the documentation of struct
drm_bridge, but the new function you're adding doesn't have one :-) I'd
drop the period here and for drm_bridge to be consistent with the rest
of the code.

> + *
> + * Drivers should call drm_bridge_init() prior adding it to the list.

s/should/shall/
s/prior adding it/prior to adding the bridge/

> + * Drivers should call drm_bridge_remove() to clean up the bridge list.

I'd replace this sentence with "Before deleting a bridge (usually when
the driver is unbound from the device), drivers shall call
drm_bridge_remove() to remove it from the global list."

>   *
>   * @bridge: bridge control structure
>   */
> @@ -89,6 +92,35 @@ void drm_bridge_remove(struct drm_bridge *bridge)
>  }
>  EXPORT_SYMBOL(drm_bridge_remove);
>  
> +/**
> + * drm_bridge_init - initialise a drm_bridge structure

initialise or initialize ? :-)

> + *
> + * @bridge: bridge control structure
> + * @funcs: control functions
> + * @dev: device associated with this drm_bridge

dev goes before funcs

> + * @timings: timing specification for the bridge; optional (may be NULL)
> + * @driver_private: pointer to the bridge driver internal context (may be NULL)

I'm not too sure about the last two parameters. Having NULL, NULL in
most callers is confusing, and having a void * as one of the parameters
means that the compiler won't catch errors if the two parameters are
reversed. I think this is quite error prone.

There are very few drivers using driver_private (I count 6 of them, with
2 additional drivers that set driver_private but never use it). How
about embedding the bridge structure in those 6 drivers and getting rid
of the field altogether ? This could be part of a separate series, but
in any case I'd drop driver_private from drm_bridge_init().

> + */
> +void drm_bridge_init(struct drm_bridge *bridge, struct device *dev,
> +		     const struct drm_bridge_funcs *funcs,
> +		     const struct drm_bridge_timings *timings,
> +		     void *driver_private)
> +{
> +	WARN_ON(!funcs || !dev);
> +
> +	bridge->dev = NULL;

NULL ? Shouldn't this be dev ?

> +	bridge->encoder = NULL;
> +	bridge->next = NULL;
> +
> +#ifdef CONFIG_OF
> +	bridge->of_node = dev->of_node;
> +#endif
> +	bridge->timings = timings;
> +	bridge->funcs = funcs;
> +	bridge->driver_private = driver_private;
> +}
> +EXPORT_SYMBOL(drm_bridge_init);
> +
>  /**
>   * drm_bridge_attach - attach the bridge to an encoder's chain
>   *
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index c0a2286a81e9..949e4f401a53 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -373,7 +373,16 @@ struct drm_bridge_timings {
>  };
>  
>  /**
> - * struct drm_bridge - central DRM bridge control structure
> + * struct drm_bridge - central DRM bridge control structure.
> + *
> + * Bridge drivers should call drm_bridge_init() to initialize a bridge
> + * driver, and then register it with drm_bridge_add().

s/bridge driver/bridge structure/ (or drm_bridge structure)

> + *
> + * Users of bridges link a bridge driver into their overall display output
> + * pipeline by calling drm_bridge_attach().
> + *
> + * Modular drivers in OF systems can query the list of registered bridges
> + * with of_drm_find_bridge().
>   */
>  struct drm_bridge {
>  	/** @dev: DRM device this bridge belongs to */
> @@ -402,6 +411,10 @@ struct drm_bridge {
>  
>  void drm_bridge_add(struct drm_bridge *bridge);
>  void drm_bridge_remove(struct drm_bridge *bridge);
> +void drm_bridge_init(struct drm_bridge *bridge, struct device *dev,
> +		     const struct drm_bridge_funcs *funcs,
> +		     const struct drm_bridge_timings *timings,
> +		     void *driver_private);
>  struct drm_bridge *of_drm_find_bridge(struct device_node *np);
>  int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>  		      struct drm_bridge *previous);

-- 
Regards,

Laurent Pinchart