linux-kernel - Re: [PATCH v1 2/5] driver core: Allow a device to wait on optional suppliers

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Date:   Tue, 05 Nov 2019 23:29:36 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Len Brown <lenb@...nel.org>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v1 2/5] driver core: Allow a device to wait on optional suppliers

On Monday, October 28, 2019 11:00:23 PM CET Saravana Kannan wrote:
> Before this change, if a device is waiting on suppliers, it's assumed
> that all those suppliers are needed for the device to probe
> successfully. This change allows marking a devices as waiting only on
> optional suppliers. This allows a device to wait on suppliers (and link
> to them as soon as they are available) without preventing the device
> from being probed.
> 
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
>  drivers/base/core.c    | 28 +++++++++++++++++++++++++---
>  include/linux/device.h |  3 +++
>  2 files changed, 28 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 17ed054c4132..48cd43a91ce6 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -480,13 +480,25 @@ EXPORT_SYMBOL_GPL(device_link_add);
>   * This function is NOT meant to be called from the probe function of the
>   * consumer but rather from code that creates/adds the consumer device.
>   */
> -static void device_link_wait_for_supplier(struct device *consumer)
> +static void device_link_wait_for_supplier(struct device *consumer,
> +					  bool need_for_probe)
>  {
>  	mutex_lock(&wfs_lock);
>  	list_add_tail(&consumer->links.needs_suppliers, &wait_for_suppliers);
> +	consumer->links.need_for_probe = need_for_probe;
>  	mutex_unlock(&wfs_lock);
>  }
>  
> +static void device_link_wait_for_mandatory_supplier(struct device *consumer)
> +{
> +	device_link_wait_for_supplier(consumer, true);
> +}
> +
> +static void device_link_wait_for_optional_supplier(struct device *consumer)
> +{
> +	device_link_wait_for_supplier(consumer, false);
> +}
> +
>  /**
>   * device_link_add_missing_supplier_links - Add links from consumer devices to
>   *					    supplier devices, leaving any
> @@ -656,7 +668,8 @@ int device_links_check_suppliers(struct device *dev)
>  	 * probe.
>  	 */
>  	mutex_lock(&wfs_lock);
> -	if (!list_empty(&dev->links.needs_suppliers)) {
> +	if (!list_empty(&dev->links.needs_suppliers) &&
> +	    dev->links.need_for_probe) {
>  		mutex_unlock(&wfs_lock);
>  		return -EPROBE_DEFER;
>  	}
> @@ -760,6 +773,15 @@ void device_links_driver_bound(struct device *dev)
>  {
>  	struct device_link *link;
>  
> +	/*
> +	 * If a device probes successfully, it's expected to have created all
> +	 * the device links it needs to or make new device links as it needs
> +	 * them. So, it no longer needs to wait on any suppliers.
> +	 */
> +	mutex_lock(&wfs_lock);
> +	list_del_init(&dev->links.needs_suppliers);
> +	mutex_unlock(&wfs_lock);
> +
>  	device_links_write_lock();
>  
>  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> @@ -2393,7 +2415,7 @@ int device_add(struct device *dev)
>  
>  	if (fwnode_has_op(dev->fwnode, add_links)
>  	    && fwnode_call_int_op(dev->fwnode, add_links, dev))
> -		device_link_wait_for_supplier(dev);
> +		device_link_wait_for_mandatory_supplier(dev, true);

Does this compile even?

The function takes one argument according to the definition above ...

>  	bus_probe_device(dev);
>  	if (parent)
> diff --git a/include/linux/device.h b/include/linux/device.h
> index f1f2aa0b19da..4fd33da9a848 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1156,6 +1156,8 @@ enum dl_dev_state {
>   * @consumers: List of links to consumer devices.
>   * @needs_suppliers: Hook to global list of devices waiting for suppliers.
>   * @defer_sync: Hook to global list of devices that have deferred sync_state.
> + * @need_for_probe: If needs_suppliers is on a list, this indicates if the
> + *		    suppliers are needed for probe or not.
>   * @status: Driver status information.
>   */
>  struct dev_links_info {
> @@ -1163,6 +1165,7 @@ struct dev_links_info {
>  	struct list_head consumers;
>  	struct list_head needs_suppliers;
>  	struct list_head defer_sync;
> +	bool need_for_probe;
>  	enum dl_dev_state status;
>  };
>  
>