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    SubjectRe: [PATCH v9 1/5] driver core: Find an existing link between two devices
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    On Tuesday, March 13, 2018 9:55:30 AM CET Vivek Gautam wrote:
    > The lists managing the device-links can be traversed to
    > find the link between two devices. The device_link_add() APIs
    > does traverse these lists to check if there's already a link
    > setup between the two devices.
    > So, add a new APIs, device_link_find(), to find an existing
    > device link between two devices - suppliers and consumers.
    >
    > Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
    > Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
    > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > ---
    >
    > * New patch added to this series.
    >
    > drivers/base/core.c | 30 +++++++++++++++++++++++++++---
    > include/linux/device.h | 2 ++
    > 2 files changed, 29 insertions(+), 3 deletions(-)
    >
    > diff --git a/drivers/base/core.c b/drivers/base/core.c
    > index 5847364f25d9..e8c9774e4ba2 100644
    > --- a/drivers/base/core.c
    > +++ b/drivers/base/core.c
    > @@ -144,6 +144,30 @@ static int device_reorder_to_tail(struct device *dev, void *not_used)
    > return 0;
    > }
    >
    > +/**
    > + * device_link_find - find any existing link between two devices.
    > + * @consumer: Consumer end of the link.
    > + * @supplier: Supplier end of the link.
    > + *
    > + * Returns pointer to the existing link between a supplier and
    > + * and consumer devices, or NULL if no link exists.
    > + */
    > +struct device_link *device_link_find(struct device *consumer,
    > + struct device *supplier)
    > +{
    > + struct device_link *link = NULL;
    > +
    > + if (!consumer || !supplier)
    > + return NULL;
    > +
    > + list_for_each_entry(link, &supplier->links.consumers, s_node)
    > + if (link->consumer == consumer)
    > + break;
    > +

    Any mutual exclusion?

    Or is the caller expected to take care of it? And if so, then how?

    > + return link;
    > +}
    > +EXPORT_SYMBOL_GPL(device_link_find);
    > +
    > /**
    > * device_link_add - Create a link between two devices.
    > * @consumer: Consumer end of the link.
    > @@ -195,9 +219,9 @@ struct device_link *device_link_add(struct device *consumer,
    > goto out;
    > }
    >
    > - list_for_each_entry(link, &supplier->links.consumers, s_node)
    > - if (link->consumer == consumer)
    > - goto out;
    > + link = device_link_find(consumer, supplier);
    > + if (link)
    > + goto out;
    >
    > link = kzalloc(sizeof(*link), GFP_KERNEL);
    > if (!link)
    > diff --git a/include/linux/device.h b/include/linux/device.h
    > index b093405ed525..13bc1884c3eb 100644
    > --- a/include/linux/device.h
    > +++ b/include/linux/device.h
    > @@ -1278,6 +1278,8 @@ extern const char *dev_driver_string(const struct device *dev);
    > struct device_link *device_link_add(struct device *consumer,
    > struct device *supplier, u32 flags);
    > void device_link_del(struct device_link *link);
    > +struct device_link *device_link_find(struct device *consumer,
    > + struct device *supplier);
    >
    > #ifdef CONFIG_PRINTK
    >
    >


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