Re: [PATCH 2/4 v6] drm/bridge: Provide a way to embed timing info in bridges

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jan 10, 2018 at 03:12:24PM +0100, Linus Walleij wrote:
> After some discussion and failed patch sets trying to convey
> the right timing information between the display engine and
> a bridge using the connector, I try instead to use an optional
> timing information container in the bridge itself, so that
> display engines can retrieve it from any bridge and use it to
> determine how to drive outputs.
> 
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v5->v6:
> - Sort forward struct declarations alphabetically
> - Switch to using DRM_BUS_FLAG_PIXDATA_[POS|NEG]EDGE to indicate
>   positive or negatice clock samling edge
> ChangeLog ->v5:
> - New patch
> ---
>  include/drm/drm_bridge.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 682d01ba920c..28c9ac6d9036 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -29,6 +29,7 @@
>  #include <drm/drm_modes.h>
>  
>  struct drm_bridge;
> +struct drm_bridge_timings;
>  struct drm_panel;
>  
>  /**
> @@ -222,6 +223,23 @@ struct drm_bridge_funcs {
>  	void (*enable)(struct drm_bridge *bridge);
>  };
>  
> +/**
> + * struct drm_bridge_timings - timing information for the bridge
> + * @sampling_edge: whether the bridge samples the digital input signal from the
> + * display engine on the positive or negative edge of the clock, this should
> + * reuse the DRM_BUS_FLAG_PIXDATA_[POS|NEG]EDGE bitwise flags from the DRM
> + * connector (bit 2 and 3 valid)
> + * @setup_time_ps: the time in picoseconds the input data lines must be stable
> + * before the clock edge
> + * @hold_time_ps: the time in picoseconds taken for the bridge to sample the
> + * input signal after the clock edge
> + */

Just a style nit: for longer kerneldoc comments for struct members the
in-line style, split up for each member, is imo better.
-Daniel

> +struct drm_bridge_timings {
> +	u32 sampling_edge;
> +	u32 setup_time_ps;
> +	u32 hold_time_ps;
> +};
> +
>  /**
>   * struct drm_bridge - central DRM bridge control structure
>   * @dev: DRM device this bridge belongs to
> @@ -229,6 +247,8 @@ struct drm_bridge_funcs {
>   * @next: the next bridge in the encoder chain
>   * @of_node: device node pointer to the bridge
>   * @list: to keep track of all added bridges
> + * @timings: the timing specification for the bridge, if any (may
> + * be NULL)
>   * @funcs: control functions
>   * @driver_private: pointer to the bridge driver's internal context
>   */
> @@ -240,6 +260,7 @@ struct drm_bridge {
>  	struct device_node *of_node;
>  #endif
>  	struct list_head list;
> +	const struct drm_bridge_timings *timings;
>  
>  	const struct drm_bridge_funcs *funcs;
>  	void *driver_private;
> -- 
> 2.14.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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