Re: [PATCH] drm: bridge: Allow daisy chaining of bridges

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 09 Apr 2015, Archit Taneja <architt@codeaurora.org> wrote:
> Allow drm_bridge objects to link to each other in order to form an encoder
> chain. The requirement for creating a chain of bridges comes because the
> MSM drm driver uses up its encoder and bridge objects for blocks within
> the SoC itself. There isn't anything left to use if the SoC display output
> is connected to an external encoder IC. Having an additional bridge
> connected to the existing bridge helps here. In general, it is possible for
> platforms to have  multiple devices between the encoder and the
> connector/panel that require some sort of configuration.
>
> We create drm bridge helper functions corresponding to each op in
> 'drm_bridge_funcs'. These helpers call the corresponding 'drm_bridge_funcs'
> op for the entire chain of bridges. These helpers are used internally by
> drm_atomic_helper.c and drm_crtc_helper.c.
>
> The drm_bridge_enable/pre_enable helpers execute enable/pre_enable ops of the
> bridge closet to the encoder, and proceed until the last bridge in the chain
> is enabled. The same holds for drm_bridge_mode_set/mode_fixup helpers. The
> drm_bridge_disable/post_disable helpers disable the last bridge in the chain
> first, and proceed until the first bridge in the chain is disabled.
>
> drm_bridge_attach() remains the same. As before, the driver calling this
> function should make sure it has set the links correctly. The order in which
> the bridges are connected to each other determines the order in which the
> calls are made. One requirement is that every bridge in the chain should point
> the parent encoder object. This is required since bridge drivers expect a
> valid encoder pointer in drm_bridge. For example, consider a chain where an
> encoder's output is connected to bridge1, and bridge1's output is connected to
> bridge2:
>
> 	/* Like before, attach bridge to an encoder */
> 	bridge1->encoder = encoder;
> 	ret = drm_bridge_attach(dev, bridge1);
> 	..
>
> 	/*
> 	 * set the first bridge's 'next' bridge to bridge2, set its encoder
> 	 * as bridge1's encoder
> 	 */
> 	bridge1->next = bridge2
> 	bridge2->encoder = bridge1->encoder;
> 	ret = drm_bridge_attach(dev, bridge2);
>
> 	...
> 	...
>
> This method of bridge chaining isn't intrusive and existing drivers that use
> drm_bridge will behave the same way as before. The bridge helpers also cleans
> up the atomic and crtc helper files a bit.
>
> Signed-off-by: Archit Taneja <architt@codeaurora.org>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 29 ++++++----------
>  drivers/gpu/drm/drm_bridge.c        | 68 +++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_crtc_helper.c   | 54 +++++++++++------------------
>  include/drm/drm_crtc.h              | 14 ++++++++
>  4 files changed, 112 insertions(+), 53 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 7e3a52b..0b4574e 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -287,14 +287,11 @@ mode_fixup(struct drm_atomic_state *state)
>  		encoder = conn_state->best_encoder;
>  		funcs = encoder->helper_private;
>  
> -		if (encoder->bridge && encoder->bridge->funcs->mode_fixup) {
> -			ret = encoder->bridge->funcs->mode_fixup(
> -					encoder->bridge, &crtc_state->mode,
> -					&crtc_state->adjusted_mode);
> -			if (!ret) {
> -				DRM_DEBUG_KMS("Bridge fixup failed\n");
> -				return -EINVAL;
> -			}
> +		ret = drm_bridge_mode_fixup(encoder->bridge, &crtc_state->mode,
> +				&crtc_state->adjusted_mode);
> +		if (!ret) {
> +			DRM_DEBUG_KMS("Bridge fixup failed\n");
> +			return -EINVAL;
>  		}
>  
>  		if (funcs->atomic_check) {
> @@ -607,8 +604,7 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  		 * Each encoder has at most one connector (since we always steal
>  		 * it away), so we won't call call disable hooks twice.
>  		 */
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->disable(encoder->bridge);
> +		drm_bridge_disable(encoder->bridge);
>  
>  		/* Right function depends upon target state. */
>  		if (connector->state->crtc && funcs->prepare)
> @@ -618,8 +614,7 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  		else
>  			funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->post_disable(encoder->bridge);
> +		drm_bridge_post_disable(encoder->bridge);
>  	}
>  
>  	for (i = 0; i < ncrtcs; i++) {
> @@ -761,9 +756,7 @@ crtc_set_mode(struct drm_device *dev, struct drm_atomic_state *old_state)
>  		 */
>  		funcs->mode_set(encoder, mode, adjusted_mode);
>  
> -		if (encoder->bridge && encoder->bridge->funcs->mode_set)
> -			encoder->bridge->funcs->mode_set(encoder->bridge,
> -							 mode, adjusted_mode);
> +		drm_bridge_mode_set(encoder->bridge, mode, adjusted_mode);
>  	}
>  }
>  
> @@ -849,16 +842,14 @@ void drm_atomic_helper_commit_post_planes(struct drm_device *dev,
>  		 * Each encoder has at most one connector (since we always steal
>  		 * it away), so we won't call call enable hooks twice.
>  		 */
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->pre_enable(encoder->bridge);
> +		drm_bridge_pre_enable(encoder->bridge);
>  
>  		if (funcs->enable)
>  			funcs->enable(encoder);
>  		else
>  			funcs->commit(encoder);
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->enable(encoder->bridge);
> +		drm_bridge_enable(encoder->bridge);
>  	}
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_commit_post_planes);
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index d1187e5..b52c387 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -66,6 +66,74 @@ extern int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge)
>  }
>  EXPORT_SYMBOL(drm_bridge_attach);
>  
> +bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
> +			const struct drm_display_mode *mode,
> +			struct drm_display_mode *adjusted_mode)
> +{
> +	bool ret = true;
> +
> +	if (!bridge)
> +		return true;
> +
> +	if (bridge->funcs->mode_fixup)
> +		ret = bridge->funcs->mode_fixup(bridge, mode, adjusted_mode);
> +
> +	return ret & drm_bridge_mode_fixup(bridge->next, mode, adjusted_mode);

Is that an intentional bitwise rather than logical AND? If it is, please
don't combine this into the return statement.

How about EXPORT_SYMBOLs for the new functions?

Other than these, the patch LGTM.

BR,
Jani.

> +}
> +
> +void drm_bridge_disable(struct drm_bridge *bridge)
> +{
> +	if (!bridge)
> +		return;
> +
> +	drm_bridge_disable(bridge->next);
> +
> +	bridge->funcs->disable(bridge);
> +}
> +
> +void drm_bridge_post_disable(struct drm_bridge *bridge)
> +{
> +	if (!bridge)
> +		return;
> +
> +	drm_bridge_post_disable(bridge->next);
> +
> +	bridge->funcs->post_disable(bridge);
> +}
> +
> +void drm_bridge_mode_set(struct drm_bridge *bridge,
> +			struct drm_display_mode *mode,
> +			struct drm_display_mode *adjusted_mode)
> +{
> +	if (!bridge)
> +		return;
> +
> +	if (bridge->funcs->mode_set)
> +		bridge->funcs->mode_set(bridge, mode, adjusted_mode);
> +
> +	drm_bridge_mode_set(bridge->next, mode, adjusted_mode);
> +}
> +
> +void drm_bridge_pre_enable(struct drm_bridge *bridge)
> +{
> +	if (!bridge)
> +		return;
> +
> +	bridge->funcs->pre_enable(bridge);
> +
> +	drm_bridge_pre_enable(bridge->next);
> +}
> +
> +void drm_bridge_enable(struct drm_bridge *bridge)
> +{
> +	if (!bridge)
> +		return;
> +
> +	bridge->funcs->enable(bridge);
> +
> +	drm_bridge_enable(bridge->next);
> +}
> +
>  #ifdef CONFIG_OF
>  struct drm_bridge *of_drm_find_bridge(struct device_node *np)
>  {
> diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
> index b1979e7..a199f49 100644
> --- a/drivers/gpu/drm/drm_crtc_helper.c
> +++ b/drivers/gpu/drm/drm_crtc_helper.c
> @@ -163,16 +163,14 @@ drm_encoder_disable(struct drm_encoder *encoder)
>  {
>  	struct drm_encoder_helper_funcs *encoder_funcs = encoder->helper_private;
>  
> -	if (encoder->bridge)
> -		encoder->bridge->funcs->disable(encoder->bridge);
> +	drm_bridge_disable(encoder->bridge);
>  
>  	if (encoder_funcs->disable)
>  		(*encoder_funcs->disable)(encoder);
>  	else
>  		(*encoder_funcs->dpms)(encoder, DRM_MODE_DPMS_OFF);
>  
> -	if (encoder->bridge)
> -		encoder->bridge->funcs->post_disable(encoder->bridge);
> +	drm_bridge_post_disable(encoder->bridge);
>  }
>  
>  static void __drm_helper_disable_unused_functions(struct drm_device *dev)
> @@ -311,13 +309,11 @@ bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
>  		if (encoder->crtc != crtc)
>  			continue;
>  
> -		if (encoder->bridge && encoder->bridge->funcs->mode_fixup) {
> -			ret = encoder->bridge->funcs->mode_fixup(
> -					encoder->bridge, mode, adjusted_mode);
> -			if (!ret) {
> -				DRM_DEBUG_KMS("Bridge fixup failed\n");
> -				goto done;
> -			}
> +		ret = drm_bridge_mode_fixup(encoder->bridge,
> +			mode, adjusted_mode);
> +		if (!ret) {
> +			DRM_DEBUG_KMS("Bridge fixup failed\n");
> +			goto done;
>  		}
>  
>  		encoder_funcs = encoder->helper_private;
> @@ -340,15 +336,13 @@ bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
>  		if (encoder->crtc != crtc)
>  			continue;
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->disable(encoder->bridge);
> +		drm_bridge_disable(encoder->bridge);
>  
>  		encoder_funcs = encoder->helper_private;
>  		/* Disable the encoders as the first thing we do. */
>  		encoder_funcs->prepare(encoder);
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->post_disable(encoder->bridge);
> +		drm_bridge_post_disable(encoder->bridge);
>  	}
>  
>  	drm_crtc_prepare_encoders(dev);
> @@ -373,9 +367,7 @@ bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
>  		encoder_funcs = encoder->helper_private;
>  		encoder_funcs->mode_set(encoder, mode, adjusted_mode);
>  
> -		if (encoder->bridge && encoder->bridge->funcs->mode_set)
> -			encoder->bridge->funcs->mode_set(encoder->bridge, mode,
> -					adjusted_mode);
> +		drm_bridge_mode_set(encoder->bridge, mode, adjusted_mode);
>  	}
>  
>  	/* Now enable the clocks, plane, pipe, and connectors that we set up. */
> @@ -386,14 +378,12 @@ bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
>  		if (encoder->crtc != crtc)
>  			continue;
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->pre_enable(encoder->bridge);
> +		drm_bridge_pre_enable(encoder->bridge);
>  
>  		encoder_funcs = encoder->helper_private;
>  		encoder_funcs->commit(encoder);
>  
> -		if (encoder->bridge)
> -			encoder->bridge->funcs->enable(encoder->bridge);
> +		drm_bridge_enable(encoder->bridge);
>  	}
>  
>  	/* Store real post-adjustment hardware mode. */
> @@ -734,23 +724,19 @@ static void drm_helper_encoder_dpms(struct drm_encoder *encoder, int mode)
>  	struct drm_bridge *bridge = encoder->bridge;
>  	struct drm_encoder_helper_funcs *encoder_funcs;
>  
> -	if (bridge) {
> -		if (mode == DRM_MODE_DPMS_ON)
> -			bridge->funcs->pre_enable(bridge);
> -		else
> -			bridge->funcs->disable(bridge);
> -	}
> +	if (mode == DRM_MODE_DPMS_ON)
> +		drm_bridge_pre_enable(bridge);
> +	else
> +		drm_bridge_disable(bridge);
>  
>  	encoder_funcs = encoder->helper_private;
>  	if (encoder_funcs->dpms)
>  		encoder_funcs->dpms(encoder, mode);
>  
> -	if (bridge) {
> -		if (mode == DRM_MODE_DPMS_ON)
> -			bridge->funcs->enable(bridge);
> -		else
> -			bridge->funcs->post_disable(bridge);
> -	}
> +	if (mode == DRM_MODE_DPMS_ON)
> +		drm_bridge_enable(bridge);
> +	else
> +		drm_bridge_post_disable(bridge);
>  }
>  
>  static int drm_helper_choose_crtc_dpms(struct drm_crtc *crtc)
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 920e21a..8fced1d 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -893,6 +893,8 @@ struct drm_bridge_funcs {
>  /**
>   * struct drm_bridge - central DRM bridge control structure
>   * @dev: DRM device this bridge belongs to
> + * @encoder: encoder to which this bridge is connected
> + * @next: the next bridge in the encoder chain
>   * @of_node: device node pointer to the bridge
>   * @list: to keep track of all added bridges
>   * @base: base mode object
> @@ -902,6 +904,7 @@ struct drm_bridge_funcs {
>  struct drm_bridge {
>  	struct drm_device *dev;
>  	struct drm_encoder *encoder;
> +	struct drm_bridge *next;
>  #ifdef CONFIG_OF
>  	struct device_node *of_node;
>  #endif
> @@ -1225,6 +1228,17 @@ extern void drm_bridge_remove(struct drm_bridge *bridge);
>  extern struct drm_bridge *of_drm_find_bridge(struct device_node *np);
>  extern int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge);
>  
> +bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
> +			const struct drm_display_mode *mode,
> +			struct drm_display_mode *adjusted_mode);
> +void drm_bridge_disable(struct drm_bridge *bridge);
> +void drm_bridge_post_disable(struct drm_bridge *bridge);
> +void drm_bridge_mode_set(struct drm_bridge *bridge,
> +			struct drm_display_mode *mode,
> +			struct drm_display_mode *adjusted_mode);
> +void drm_bridge_pre_enable(struct drm_bridge *bridge);
> +void drm_bridge_enable(struct drm_bridge *bridge);
> +
>  extern int drm_encoder_init(struct drm_device *dev,
>  			    struct drm_encoder *encoder,
>  			    const struct drm_encoder_funcs *funcs,
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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