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Date:   Wed, 6 Oct 2021 20:07:11 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH v2 02/34] component: Introduce the aggregate bus_type

On Wed, Oct 6, 2021 at 12:38 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> The component driver only provides 'bind' and 'unbind' callbacks to tell
> the host driver that it is time to assemble the aggregate driver now
> that all the components have probed. The component driver model doesn't
> attempt to resolve runtime PM or suspend/resume ordering, and explicitly
> mentions this in the code. This lack of support leads to some pretty
> gnarly usages of the 'prepare' and 'complete' power management hooks in
> drivers that host the aggregate device, and it fully breaks down when
> faced with ordering shutdown between the various components, the
> aggregate driver, and the host driver that registers the whole thing.
>
> In a concrete example, the MSM display driver at drivers/gpu/drm/msm is
> using 'prepare' and 'complete' to call the drm helpers
> drm_mode_config_helper_suspend() and drm_mode_config_helper_resume()
> respectively, so that it can move the aggregate driver suspend/resume
> callbacks to be before and after the components that make up the drm
> device call any suspend/resume hooks they have. This only works as long
> as the component devices don't do anything in their own 'prepare' and
> 'complete' callbacks. If they did, then the ordering would be incorrect
> and we would be doing something in the component drivers before the
> aggregate driver could do anything. Yuck!
>
> Similarly, when trying to add shutdown support to the MSM driver we run
> across a problem where we're trying to shutdown the drm device via
> drm_atomic_helper_shutdown(), but some of the devices in the encoder
> chain have already been shutdown. This time, the component devices
> aren't the problem (although they could be if they did anything in their
> shutdown callbacks), but there's a DSI to eDP bridge in the encoder
> chain that has already been shutdown before the driver hosting the
> aggregate device runs shutdown. The ordering of driver probe is like
> this:
>
>  1. msm_pdev_probe() (host driver)
>  2. DSI bridge
>  3. aggregate bind
>
> When it comes to shutdown we have this order:
>
>  1. DSI bridge
>  2. msm_pdev_shutdown() (host driver)
>
> and so the bridge is already off, but we want to communicate to it to
> turn things off on the display during msm_pdev_shutdown(). Double yuck!
> Unfortunately, this time we can't split shutdown into multiple phases
> and swap msm_pdev_shutdown() with the DSI bridge.
>
> Let's make the component driver into an actual device driver that has
> probe/remove/shutdown functions. The driver will only be bound to the
> aggregate device once all component drivers have called component_add()
> to indicate they're ready to assemble the aggregate driver. This allows
> us to attach shutdown logic (and in the future runtime PM logic) to the
> aggregate driver so that it runs the hooks in the correct order.
>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Rob Clark <robdclark@...il.com>
> Cc: Russell King <rmk+kernel@....linux.org.uk>
> Cc: Saravana Kannan <saravanak@...gle.com>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>  drivers/base/component.c  | 454 +++++++++++++++++++++++++++-----------
>  include/linux/component.h |  62 +++++-
>  2 files changed, 381 insertions(+), 135 deletions(-)
>
> diff --git a/drivers/base/component.c b/drivers/base/component.c
> index 0a41bbe14981..d99e99cabb99 100644
> --- a/drivers/base/component.c
> +++ b/drivers/base/component.c
> @@ -15,6 +15,9 @@
>  #include <linux/mutex.h>
>  #include <linux/slab.h>
>  #include <linux/debugfs.h>
> +#include <linux/pm_runtime.h>
> +
> +#include "base.h"
>
>  /**
>   * DOC: overview
> @@ -38,8 +41,8 @@
>   *
>   * Aggregate drivers first assemble a component match list of what they need
>   * using component_match_add(). This is then registered as an aggregate driver
> - * using component_master_add_with_match(), and unregistered using
> - * component_master_del().
> + * using component_aggregate_register(), and unregistered using
> + * component_aggregate_unregister().
>   */
>
>  struct component;
> @@ -60,17 +63,20 @@ struct component_match {
>  };
>
>  struct aggregate_device {
> -       struct list_head node;
> -       bool bound;
> -
>         const struct component_master_ops *ops;
>         struct device *parent;
>         struct device dev;
>         struct component_match *match;
> +       struct aggregate_driver *adrv;
>
>         int id;
>  };
>
> +static inline struct aggregate_device *to_aggregate_device(struct device *d)
> +{
> +       return container_of(d, struct aggregate_device, dev);
> +}
> +
>  struct component {
>         struct list_head node;
>         struct aggregate_device *adev;
> @@ -79,11 +85,11 @@ struct component {
>         const struct component_ops *ops;
>         int subcomponent;
>         struct device *dev;
> +       struct device_link *link;
>  };
>
>  static DEFINE_MUTEX(component_mutex);
>  static LIST_HEAD(component_list);
> -static LIST_HEAD(aggregate_devices);
>
>  static DEFINE_IDA(aggregate_ida);
>
> @@ -101,7 +107,7 @@ static int component_devices_show(struct seq_file *s, void *data)
>         seq_printf(s, "%-40s %20s\n", "aggregate_device name", "status");
>         seq_puts(s, "-------------------------------------------------------------\n");
>         seq_printf(s, "%-40s %20s\n\n",
> -                  dev_name(m->parent), m->bound ? "bound" : "not bound");
> +                  dev_name(m->parent), m->dev.driver ? "bound" : "not bound");
>
>         seq_printf(s, "%-40s %20s\n", "device name", "status");
>         seq_puts(s, "-------------------------------------------------------------\n");
> @@ -149,16 +155,21 @@ static void component_master_debugfs_del(struct aggregate_device *m)
>
>  #endif
>
> -static struct aggregate_device *__aggregate_find(struct device *parent,
> -       const struct component_master_ops *ops)
> +struct aggregate_bus_find_data {
> +       const struct component_master_ops *ops;
> +       struct device *parent;
> +};
> +
> +static int aggregate_bus_find_match(struct device *dev, const void *_data)
>  {
> -       struct aggregate_device *m;
> +       struct aggregate_device *adev = to_aggregate_device(dev);
> +       const struct aggregate_bus_find_data *data = _data;
>
> -       list_for_each_entry(m, &aggregate_devices, node)
> -               if (m->parent == parent && (!ops || m->ops == ops))
> -                       return m;
> +       if (adev->parent == data->parent &&
> +           (!data->ops || adev->ops == data->ops))
> +               return 1;
>
> -       return NULL;
> +       return 0;
>  }
>
>  static struct component *find_component(struct aggregate_device *adev,
> @@ -185,7 +196,6 @@ static int find_components(struct aggregate_device *adev)
>  {
>         struct component_match *match = adev->match;
>         size_t i;
> -       int ret = 0;
>
>         /*
>          * Scan the array of match functions and attach
> @@ -194,6 +204,7 @@ static int find_components(struct aggregate_device *adev)
>         for (i = 0; i < match->num; i++) {
>                 struct component_match_array *mc = &match->compare[i];
>                 struct component *c;
> +               bool duplicate;
>
>                 dev_dbg(adev->parent, "Looking for component %zu\n", i);
>
> @@ -201,20 +212,27 @@ static int find_components(struct aggregate_device *adev)
>                         continue;
>
>                 c = find_component(adev, mc);
> -               if (!c) {
> -                       ret = -ENXIO;
> -                       break;
> -               }
> +               if (!c)
> +                       return 0;
>
> +               duplicate = !!c->adev;
>                 dev_dbg(adev->parent, "found component %s, duplicate %u\n",
> -                       dev_name(c->dev), !!c->adev);
> +                       dev_name(c->dev), duplicate);
>
>                 /* Attach this component to the adev */
> -               match->compare[i].duplicate = !!c->adev;
> +               match->compare[i].duplicate = duplicate;
>                 match->compare[i].component = c;
> +               if (duplicate)
> +                       continue;
> +
> +               /* Matches put in component_del() */
> +               get_device(&adev->dev);
> +               c->link = device_link_add(&adev->dev, c->dev,
> +                                         DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME);

Remove the STATELESS flag and you'll get a bunch of other stuff done for free:
1. The aggregate device would get force unbound when the component
devices unbind.
2. You don't need to explicitly keep track of and delete the link. If
either of the devices get deleted, it'll get deleted automatically.
3. It will avoid useless probe attempts of the aggregate device before
all the component devices are probed.

-Saravana

>                 c->adev = adev;
>         }
> -       return ret;
> +
> +       return 1;
>  }
>
>  /* Detach component from associated aggregate_device */
> @@ -228,72 +246,6 @@ static void remove_component(struct aggregate_device *adev, struct component *c)
>                         adev->match->compare[i].component = NULL;
>  }
>
> -/*
> - * Try to bring up an aggregate device.  If component is NULL, we're interested
> - * in this aggregate device, otherwise it's a component which must be present
> - * to try and bring up the aggregate device.
> - *
> - * Returns 1 for successful bringup, 0 if not ready, or -ve errno.
> - */
> -static int try_to_bring_up_aggregate_device(struct aggregate_device *adev,
> -       struct component *component)
> -{
> -       int ret;
> -
> -       dev_dbg(adev->parent, "trying to bring up adev\n");
> -
> -       if (find_components(adev)) {
> -               dev_dbg(adev->parent, "master has incomplete components\n");
> -               return 0;
> -       }
> -
> -       if (component && component->adev != adev) {
> -               dev_dbg(adev->parent, "master is not for this component (%s)\n",
> -                       dev_name(component->dev));
> -               return 0;
> -       }
> -
> -       if (!devres_open_group(adev->parent, NULL, GFP_KERNEL))
> -               return -ENOMEM;
> -
> -       /* Found all components */
> -       ret = adev->ops->bind(adev->parent);
> -       if (ret < 0) {
> -               devres_release_group(adev->parent, NULL);
> -               if (ret != -EPROBE_DEFER)
> -                       dev_info(adev->parent, "adev bind failed: %d\n", ret);
> -               return ret;
> -       }
> -
> -       adev->bound = true;
> -       return 1;
> -}
> -
> -static int try_to_bring_up_masters(struct component *component)
> -{
> -       struct aggregate_device *adev;
> -       int ret = 0;
> -
> -       list_for_each_entry(adev, &aggregate_devices, node) {
> -               if (!adev->bound) {
> -                       ret = try_to_bring_up_aggregate_device(adev, component);
> -                       if (ret != 0)
> -                               break;
> -               }
> -       }
> -
> -       return ret;
> -}
> -
> -static void take_down_aggregate_device(struct aggregate_device *adev)
> -{
> -       if (adev->bound) {
> -               adev->ops->unbind(adev->parent);
> -               devres_release_group(adev->parent, NULL);
> -               adev->bound = false;
> -       }
> -}
> -
>  static void devm_component_match_release(struct device *parent, void *res)
>  {
>         struct component_match *match = res;
> @@ -437,7 +389,6 @@ static void free_aggregate_device(struct aggregate_device *adev)
>         int i;
>
>         component_master_debugfs_del(adev);
> -       list_del(&adev->node);
>
>         if (match) {
>                 for (i = 0; i < match->num; i++) {
> @@ -451,20 +402,143 @@ static void free_aggregate_device(struct aggregate_device *adev)
>         kfree(adev);
>  }
>
> -/**
> - * component_master_add_with_match - register an aggregate driver
> - * @parent: parent device of the aggregate driver
> - * @ops: callbacks for the aggregate driver
> - * @match: component match list for the aggregate driver
> - *
> - * Registers a new aggregate driver consisting of the components added to @match
> - * by calling one of the component_match_add() functions. Once all components in
> - * @match are available, it will be assembled by calling
> - * &component_master_ops.bind from @ops. Must be unregistered by calling
> - * component_master_del().
> - */
> -int component_master_add_with_match(struct device *parent,
> -       const struct component_master_ops *ops,
> +static void aggregate_device_release(struct device *dev)
> +{
> +       struct aggregate_device *adev = to_aggregate_device(dev);
> +
> +       free_aggregate_device(adev);
> +}
> +
> +static int aggregate_device_match(struct device *dev, struct device_driver *drv)
> +{
> +       const struct aggregate_driver *adrv = to_aggregate_driver(drv);
> +       struct aggregate_device *adev = to_aggregate_device(dev);
> +       int ret;
> +
> +       /* Is this driver associated with this device */
> +       if (adrv != adev->adrv)
> +               return 0;
> +
> +       /* Should we start to assemble? */
> +       mutex_lock(&component_mutex);
> +       ret = find_components(adev);
> +       mutex_unlock(&component_mutex);
> +
> +       return ret;
> +}
> +
> +/* TODO: Remove once all aggregate drivers use component_aggregate_register() */
> +static int component_probe_bind(struct aggregate_device *adev)
> +{
> +       return adev->ops->bind(adev->parent);
> +}
> +
> +static void component_remove_unbind(struct aggregate_device *adev)
> +{
> +       adev->ops->unbind(adev->parent);
> +}
> +
> +static int aggregate_driver_probe(struct device *dev)
> +{
> +       const struct aggregate_driver *adrv = to_aggregate_driver(dev->driver);
> +       struct aggregate_device *adev = to_aggregate_device(dev);
> +       bool modern = adrv->probe != component_probe_bind;
> +       int ret;
> +
> +       /* Only do runtime PM when drivers migrate */
> +       if (modern) {
> +               pm_runtime_get_noresume(dev);
> +               pm_runtime_set_active(dev);
> +               pm_runtime_enable(dev);
> +       }
> +
> +       mutex_lock(&component_mutex);
> +       if (devres_open_group(adev->parent, NULL, GFP_KERNEL)) {
> +               ret = adrv->probe(adev);
> +               if (ret)
> +                       devres_release_group(adev->parent, NULL);
> +       } else {
> +               ret = -ENOMEM;
> +       }
> +       mutex_unlock(&component_mutex);
> +
> +       if (ret && modern) {
> +               pm_runtime_disable(dev);
> +               pm_runtime_set_suspended(dev);
> +               pm_runtime_put_noidle(dev);
> +       }
> +
> +       return ret;
> +}
> +
> +static int aggregate_driver_remove(struct device *dev)
> +{
> +       const struct aggregate_driver *adrv = to_aggregate_driver(dev->driver);
> +       struct aggregate_device *adev = to_aggregate_device(dev);
> +       bool modern = adrv->remove != component_remove_unbind;
> +
> +       /* Only do runtime PM when drivers migrate */
> +       if (modern)
> +               pm_runtime_get_sync(dev);
> +       adrv->remove(to_aggregate_device(dev));
> +       devres_release_group(adev->parent, NULL);
> +       if (!modern)
> +               return 0;
> +
> +       pm_runtime_put_noidle(dev);
> +
> +       pm_runtime_disable(dev);
> +       pm_runtime_set_suspended(dev);
> +       pm_runtime_put_noidle(dev);
> +
> +       return 0;
> +}
> +
> +static void aggregate_driver_shutdown(struct device *dev)
> +{
> +       const struct aggregate_driver *adrv = to_aggregate_driver(dev->driver);
> +
> +       if (adrv && adrv->shutdown)
> +               adrv->shutdown(to_aggregate_device(dev));
> +}
> +
> +static struct bus_type aggregate_bus_type = {
> +       .name           = "aggregate",
> +       .match          = aggregate_device_match,
> +       .probe          = aggregate_driver_probe,
> +       .remove         = aggregate_driver_remove,
> +       .shutdown       = aggregate_driver_shutdown,
> +};
> +
> +/* Callers take ownership of return value, should call put_device() */
> +static struct aggregate_device *__aggregate_find(struct device *parent,
> +       const struct component_master_ops *ops)
> +{
> +       struct device *dev;
> +       struct aggregate_bus_find_data data = {
> +               .ops = ops,
> +               .parent = parent,
> +       };
> +
> +       dev = bus_find_device(&aggregate_bus_type, NULL, &data,
> +                             aggregate_bus_find_match);
> +
> +       return dev ? to_aggregate_device(dev) : NULL;
> +}
> +
> +static int aggregate_driver_register(struct aggregate_driver *adrv)
> +{
> +       adrv->driver.bus = &aggregate_bus_type;
> +       return driver_register(&adrv->driver);
> +}
> +
> +static void aggregate_driver_unregister(struct aggregate_driver *adrv)
> +{
> +       driver_unregister(&adrv->driver);
> +}
> +
> +static struct aggregate_device *aggregate_device_add(struct device *parent,
> +       const struct component_master_ops *ops, struct aggregate_driver *adrv,
>         struct component_match *match)
>  {
>         struct aggregate_device *adev;
> @@ -473,40 +547,114 @@ int component_master_add_with_match(struct device *parent,
>         /* Reallocate the match array for its true size */
>         ret = component_match_realloc(match, match->num);
>         if (ret)
> -               return ret;
> +               return ERR_PTR(ret);
>
>         adev = kzalloc(sizeof(*adev), GFP_KERNEL);
>         if (!adev)
> -               return -ENOMEM;
> +               return ERR_PTR(-ENOMEM);
>
>         id = ida_alloc(&aggregate_ida, GFP_KERNEL);
>         if (id < 0) {
>                 kfree(adev);
> -               return id;
> +               return ERR_PTR(id);
>         }
>
>         adev->id = id;
>         adev->parent = parent;
> +       adev->dev.bus = &aggregate_bus_type;
> +       adev->dev.release = aggregate_device_release;
>         adev->ops = ops;
>         adev->match = match;
> +       adev->adrv = adrv;
>         dev_set_name(&adev->dev, "aggregate%d", id);
>
> +       ret = device_register(&adev->dev);
> +       if (ret) {
> +               put_device(&adev->dev);
> +               return ERR_PTR(ret);
> +       }
> +
>         component_master_debugfs_add(adev);
> -       /* Add to the list of available aggregate devices. */
> -       mutex_lock(&component_mutex);
> -       list_add(&adev->node, &aggregate_devices);
>
> -       ret = try_to_bring_up_aggregate_device(adev, NULL);
> +       return adev;
> +}
> +
> +/**
> + * component_master_add_with_match - register an aggregate driver
> + * @parent: parent device of the aggregate driver
> + * @ops: callbacks for the aggregate driver
> + * @match: component match list for the aggregate driver
> + *
> + * Registers a new aggregate driver consisting of the components added to @match
> + * by calling one of the component_match_add() functions. Once all components in
> + * @match are available, it will be assembled by calling
> + * &component_master_ops.bind from @ops. Must be unregistered by calling
> + * component_master_del().
> + *
> + * Deprecated: Use component_aggregate_register() instead.
> + */
> +int component_master_add_with_match(struct device *parent,
> +       const struct component_master_ops *ops,
> +       struct component_match *match)
> +{
> +       struct aggregate_driver *adrv;
> +       struct aggregate_device *adev;
> +       int ret = 0;
> +
> +       adrv = kzalloc(sizeof(*adrv), GFP_KERNEL);
> +       if (!adrv)
> +               return -ENOMEM;
>
> -       if (ret < 0)
> -               free_aggregate_device(adev);
> +       adev = aggregate_device_add(parent, ops, adrv, match);
> +       if (IS_ERR(adev)) {
> +               ret = PTR_ERR(adev);
> +               goto err;
> +       }
>
> -       mutex_unlock(&component_mutex);
> +       adrv->probe = component_probe_bind;
> +       adrv->remove = component_remove_unbind;
> +       adrv->driver.owner = THIS_MODULE;
> +       adrv->driver.name = dev_name(&adev->dev);
> +
> +       ret = aggregate_driver_register(adrv);
> +       if (!ret)
> +               return 0;
>
> -       return ret < 0 ? ret : 0;
> +       put_device(&adev->dev);
> +err:
> +       kfree(adrv);
> +       return ret;
>  }
>  EXPORT_SYMBOL_GPL(component_master_add_with_match);
>
> +/**
> + * component_aggregate_register - register an aggregate driver
> + * @parent: parent device of the aggregate driver
> + * @adrv: aggregate driver to register
> + *
> + * Registers a new aggregate driver consisting of the components added to @adrv.match
> + * by calling one of the component_match_add() functions. Once all components in
> + * @match are available, the aggregate driver will be assembled by calling
> + * &adrv.bind. Must be unregistered by calling component_aggregate_unregister().
> + */
> +int component_aggregate_register(struct device *parent,
> +       struct aggregate_driver *adrv, struct component_match *match)
> +{
> +       struct aggregate_device *adev;
> +       int ret;
> +
> +       adev = aggregate_device_add(parent, NULL, adrv, match);
> +       if (IS_ERR(adev))
> +               return PTR_ERR(adev);
> +
> +       ret = aggregate_driver_register(adrv);
> +       if (ret)
> +               put_device(&adev->dev);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(component_aggregate_register);
> +
>  /**
>   * component_master_del - unregister an aggregate driver
>   * @parent: parent device of the aggregate driver
> @@ -515,22 +663,60 @@ EXPORT_SYMBOL_GPL(component_master_add_with_match);
>   * Unregisters an aggregate driver registered with
>   * component_master_add_with_match(). If necessary the aggregate driver is first
>   * disassembled by calling &component_master_ops.unbind from @ops.
> + *
> + * Deprecated: Use component_aggregate_unregister() instead.
>   */
>  void component_master_del(struct device *parent,
>         const struct component_master_ops *ops)
>  {
>         struct aggregate_device *adev;
> +       struct aggregate_driver *adrv;
> +       struct device_driver *drv;
>
>         mutex_lock(&component_mutex);
>         adev = __aggregate_find(parent, ops);
> +       mutex_unlock(&component_mutex);
> +
>         if (adev) {
> -               take_down_aggregate_device(adev);
> -               free_aggregate_device(adev);
> +               drv = adev->dev.driver;
> +               if (drv) {
> +                       adrv = to_aggregate_driver(drv);
> +                       aggregate_driver_unregister(adrv);
> +                       kfree(adrv);
> +               }
> +
> +               device_unregister(&adev->dev);
>         }
> -       mutex_unlock(&component_mutex);
> +       put_device(&adev->dev);
>  }
>  EXPORT_SYMBOL_GPL(component_master_del);
>
> +/**
> + * component_aggregate_unregister - unregister an aggregate driver
> + * @parent: parent device of the aggregate driver
> + * @adrv: registered aggregate driver
> + *
> + * Unregisters an aggregate driver registered with
> + * component_aggregate_register(). If necessary the aggregate driver is first
> + * disassembled.
> + */
> +void component_aggregate_unregister(struct device *parent,
> +       struct aggregate_driver *adrv)
> +{
> +       struct aggregate_device *adev;
> +
> +       mutex_lock(&component_mutex);
> +       adev = __aggregate_find(parent, NULL);
> +       mutex_unlock(&component_mutex);
> +
> +       if (adev)
> +               device_unregister(&adev->dev);
> +       put_device(&adev->dev);
> +
> +       aggregate_driver_unregister(adrv);
> +}
> +EXPORT_SYMBOL_GPL(component_aggregate_unregister);
> +
>  static void component_unbind(struct component *component,
>         struct aggregate_device *adev, void *data)
>  {
> @@ -571,6 +757,8 @@ void component_unbind_all(struct device *parent, void *data)
>                         c = adev->match->compare[i].component;
>                         component_unbind(c, adev, data);
>                 }
> +
> +       put_device(&adev->dev);
>  }
>  EXPORT_SYMBOL_GPL(component_unbind_all);
>
> @@ -665,6 +853,7 @@ int component_bind_all(struct device *parent, void *data)
>                                 component_unbind(c, adev, data);
>                         }
>         }
> +       put_device(&adev->dev);
>
>         return ret;
>  }
> @@ -674,7 +863,6 @@ static int __component_add(struct device *dev, const struct component_ops *ops,
>         int subcomponent)
>  {
>         struct component *component;
> -       int ret;
>
>         component = kzalloc(sizeof(*component), GFP_KERNEL);
>         if (!component)
> @@ -688,18 +876,10 @@ static int __component_add(struct device *dev, const struct component_ops *ops,
>
>         mutex_lock(&component_mutex);
>         list_add_tail(&component->node, &component_list);
> -
> -       ret = try_to_bring_up_masters(component);
> -       if (ret < 0) {
> -               if (component->adev)
> -                       remove_component(component->adev, component);
> -               list_del(&component->node);
> -
> -               kfree(component);
> -       }
>         mutex_unlock(&component_mutex);
>
> -       return ret < 0 ? ret : 0;
> +       /* Try to bind */
> +       return bus_rescan_devices(&aggregate_bus_type);
>  }
>
>  /**
> @@ -763,6 +943,7 @@ EXPORT_SYMBOL_GPL(component_add);
>   */
>  void component_del(struct device *dev, const struct component_ops *ops)
>  {
> +       struct aggregate_device *adev = NULL;
>         struct component *c, *component = NULL;
>
>         mutex_lock(&component_mutex);
> @@ -774,13 +955,26 @@ void component_del(struct device *dev, const struct component_ops *ops)
>                 }
>
>         if (component && component->adev) {
> -               take_down_aggregate_device(component->adev);
> -               remove_component(component->adev, component);
> +               adev = component->adev;
> +               remove_component(adev, component);
>         }
>
>         mutex_unlock(&component_mutex);
>
> +       if (adev) {
> +               /* Force unbind */
> +               device_driver_detach(&adev->dev);
> +               device_link_del(component->link);
> +               put_device(&adev->dev);
> +       }
> +
>         WARN_ON(!component);
>         kfree(component);
>  }
>  EXPORT_SYMBOL_GPL(component_del);
> +
> +static int __init aggregate_bus_init(void)
> +{
> +       return bus_register(&aggregate_bus_type);
> +}
> +postcore_initcall(aggregate_bus_init);
> diff --git a/include/linux/component.h b/include/linux/component.h
> index 71bfc3862633..95d1b23ede8a 100644
> --- a/include/linux/component.h
> +++ b/include/linux/component.h
> @@ -3,9 +3,7 @@
>  #define COMPONENT_H
>
>  #include <linux/stddef.h>
> -
> -
> -struct device;
> +#include <linux/device.h>
>
>  /**
>   * struct component_ops - callbacks for component drivers
> @@ -82,11 +80,65 @@ struct component_master_ops {
>         void (*unbind)(struct device *master);
>  };
>
> +struct component_match;
> +
> +/**
> + * struct aggregate_driver - Aggregate driver (made up of other drivers)
> + * @driver: device driver
> + * @match: component match list
> + */
> +struct aggregate_driver {
> +       /**
> +        * @probe:
> +        *
> +        * Called when all components or the aggregate driver, as specified in
> +        * the @match list are
> +        * ready. Usually there are 3 steps to bind an aggregate driver:
> +        *
> +        * 1. Allocate a struct aggregate_driver.
> +        *
> +        * 2. Bind all components to the aggregate driver by calling
> +        *    component_bind_all() with the aggregate driver structure as opaque
> +        *    pointer data.
> +        *
> +        * 3. Register the aggregate driver with the subsystem to publish its
> +        *    interfaces.
> +        */
> +       int (*probe)(struct aggregate_device *adev);
> +       /**
> +        * @remove:
> +        *
> +        * Called when either the aggregate driver, using
> +        * component_aggregate_unregister(), or one of its components, using
> +        * component_del(), is unregistered.
> +        */
> +       void (*remove)(struct aggregate_device *adev);
> +       /**
> +        * @shutdown:
> +        *
> +        * Called when the system is shutting down.
> +        */
> +       void (*shutdown)(struct aggregate_device *adev);
> +
> +       struct device_driver    driver;
> +};
> +
> +static inline struct aggregate_driver *to_aggregate_driver(struct device_driver *d)
> +{
> +       if (!d)
> +               return NULL;
> +
> +       return container_of(d, struct aggregate_driver, driver);
> +}
> +
> +int component_aggregate_register(struct device *parent,
> +       struct aggregate_driver *adrv, struct component_match *match);
> +void component_aggregate_unregister(struct device *parent,
> +       struct aggregate_driver *adrv);
> +
>  void component_master_del(struct device *,
>         const struct component_master_ops *);
>
> -struct component_match;
> -
>  int component_master_add_with_match(struct device *,
>         const struct component_master_ops *, struct component_match *);
>  void component_match_add_release(struct device *master,
> --
> https://chromeos.dev
>

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