Re: [PATCH v2] drm: bridge: Allow daisy chaining of bridges

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On Fri, May 8, 2015 at 6:11 AM, Archit Taneja <architt@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>

Looks good. But I guess we probably should have some headerdoc for the
new fxns, and somewhere a comment about not calling the bridge vfuncs
directly but using the new helper funcs which handle the chaining.  I
guess it isn't *as* critical as it would be if these were things
intended to be called by drivers, rather than just from core, but all
the same I think it would be a good idea.  With that,

Reviewed-by: Rob Clark <robdclark@xxxxxxxxx>


> ---
> v2:
> - Add EXPORT_SYMBOL for the new functions
> - Fix logic issue in mode_fixup()
>
>  drivers/gpu/drm/drm_atomic_helper.c | 29 +++++---------
>  drivers/gpu/drm/drm_bridge.c        | 76 +++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_crtc_helper.c   | 54 ++++++++++----------------
>  include/drm/drm_crtc.h              | 14 +++++++
>  4 files changed, 120 insertions(+), 53 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 1d2ca52..d6c85c0 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -281,14 +281,11 @@ 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_ATOMIC("Bridge fixup failed\n");
> -                               return -EINVAL;
> -                       }
> +               ret = drm_bridge_mode_fixup(encoder->bridge, &crtc_state->mode,
> +                               &crtc_state->adjusted_mode);
> +               if (!ret) {
> +                       DRM_DEBUG_ATOMIC("Bridge fixup failed\n");
> +                       return -EINVAL;
>                 }
>
>                 if (funcs->atomic_check) {
> @@ -578,8 +575,7 @@ 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 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)
> @@ -589,8 +585,7 @@ 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_each_crtc_in_state(old_state, crtc, old_crtc_state, i) {
> @@ -713,9 +708,7 @@ crtc_set_mode(struct drm_device *dev, struct drm_atomic_state *old_state)
>                 if (funcs->mode_set)
>                         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);
>         }
>  }
>
> @@ -809,16 +802,14 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>                  * Each encoder has at most one connector (since we always steal
>                  * it away), so we won't 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_modeset_enables);
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index eaa5790..98c39f6 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -66,6 +66,82 @@ 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);
> +
> +       ret = ret && drm_bridge_mode_fixup(bridge->next, mode, adjusted_mode);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(drm_bridge_mode_fixup);
> +
> +void drm_bridge_disable(struct drm_bridge *bridge)
> +{
> +       if (!bridge)
> +               return;
> +
> +       drm_bridge_disable(bridge->next);
> +
> +       bridge->funcs->disable(bridge);
> +}
> +EXPORT_SYMBOL(drm_bridge_disable);
> +
> +void drm_bridge_post_disable(struct drm_bridge *bridge)
> +{
> +       if (!bridge)
> +               return;
> +
> +       drm_bridge_post_disable(bridge->next);
> +
> +       bridge->funcs->post_disable(bridge);
> +}
> +EXPORT_SYMBOL(drm_bridge_post_disable);
> +
> +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);
> +}
> +EXPORT_SYMBOL(drm_bridge_mode_set);
> +
> +void drm_bridge_pre_enable(struct drm_bridge *bridge)
> +{
> +       if (!bridge)
> +               return;
> +
> +       bridge->funcs->pre_enable(bridge);
> +
> +       drm_bridge_pre_enable(bridge->next);
> +}
> +EXPORT_SYMBOL(drm_bridge_pre_enable);
> +
> +void drm_bridge_enable(struct drm_bridge *bridge)
> +{
> +       if (!bridge)
> +               return;
> +
> +       bridge->funcs->enable(bridge);
> +
> +       drm_bridge_enable(bridge->next);
> +}
> +EXPORT_SYMBOL(drm_bridge_enable);
> +
>  #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 ab00286..ff9b338 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)
>  {
>         const 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)
> @@ -312,13 +310,11 @@ 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;
> @@ -343,15 +339,13 @@ 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);
> @@ -376,9 +370,7 @@ 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. */
> @@ -389,14 +381,12 @@ 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);
>         }
>
>         /* Calculate and store various constants which
> @@ -735,23 +725,19 @@ static void drm_helper_encoder_dpms(struct drm_encoder *encoder, int mode)
>         struct drm_bridge *bridge = encoder->bridge;
>         const 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 ca71c03..db830f4 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -895,6 +895,8 @@ 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
> @@ -904,6 +906,7 @@ 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
> @@ -1230,6 +1233,17 @@ 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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