Re: [PATCH v4 01/18] fpga: bridge: support getting bridge from device

From: Moritz Fischer
Date: Mon Sep 18 2017 - 13:58:16 EST

On Wed, Sep 13, 2017 at 03:48:24PM -0500, Alan Tull wrote:
> Add two functions for getting the FPGA bridge from the device
> rather than device tree node. This is to enable writing code
> that will support using FPGA bridges without device tree.
> Rename one old function to make it clear that it is device
> tree-ish. This leaves us with 3 functions for getting a bridge:
>
> * fpga_bridge_get
> Get the bridge given the device.
>
> * fpga_bridges_get_to_list
> Given the device, get the bridge and add it to a list.
>
> * of_fpga_bridges_get_to_list
> Renamed from priviously existing fpga_bridges_get_to_list.
> Given the device node, get the bridge and add it to a list.
>
> Signed-off-by: Alan Tull <atull@xxxxxxxxxx>
> ---
> v2: use list_for_each_entry
> static the bridge_list_lock
> update copyright and author email
> v3: no change to this patch in this version of patchset
> v4: no change to this patch in this version of patchset
> ---
> drivers/fpga/fpga-bridge.c | 110 +++++++++++++++++++++++++++++++--------
> drivers/fpga/fpga-region.c | 11 ++--
> include/linux/fpga/fpga-bridge.h | 7 ++-
> 3 files changed, 100 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
> index fcd2bd3..af6d97e 100644
> --- a/drivers/fpga/fpga-bridge.c
> +++ b/drivers/fpga/fpga-bridge.c
> @@ -2,6 +2,7 @@
> * FPGA Bridge Framework Driver
> *
> * Copyright (C) 2013-2016 Altera Corporation, All Rights Reserved.
> + * Copyright (C) 2017 Intel Corporation
> *
> * This program is free software; you can redistribute it and/or modify it
> * under the terms and conditions of the GNU General Public License,
> @@ -70,29 +71,12 @@ int fpga_bridge_disable(struct fpga_bridge *bridge)
> }
> EXPORT_SYMBOL_GPL(fpga_bridge_disable);
>
> -/**
> - * of_fpga_bridge_get - get an exclusive reference to a fpga bridge
> - *
> - * @np: node pointer of a FPGA bridge
> - * @info: fpga image specific information
> - *
> - * Return fpga_bridge struct if successful.
> - * Return -EBUSY if someone already has a reference to the bridge.
> - * Return -ENODEV if @np is not a FPGA Bridge.
> - */
> -struct fpga_bridge *of_fpga_bridge_get(struct device_node *np,
> - struct fpga_image_info *info)
> -
> +struct fpga_bridge *__fpga_bridge_get(struct device *dev,
> + struct fpga_image_info *info)
> {
> - struct device *dev;
> struct fpga_bridge *bridge;
> int ret = -ENODEV;
>
> - dev = class_find_device(fpga_bridge_class, NULL, np,
> - fpga_bridge_of_node_match);
> - if (!dev)
> - goto err_dev;
> -
> bridge = to_fpga_bridge(dev);
> if (!bridge)
> goto err_dev;
> @@ -117,8 +101,58 @@ struct fpga_bridge *of_fpga_bridge_get(struct device_node *np,
> put_device(dev);
> return ERR_PTR(ret);
> }
> +
> +/**
> + * of_fpga_bridge_get - get an exclusive reference to a fpga bridge
> + *
> + * @np: node pointer of a FPGA bridge
> + * @info: fpga image specific information
> + *
> + * Return fpga_bridge struct if successful.
> + * Return -EBUSY if someone already has a reference to the bridge.
> + * Return -ENODEV if @np is not a FPGA Bridge.
> + */
> +struct fpga_bridge *of_fpga_bridge_get(struct device_node *np,
> + struct fpga_image_info *info)
> +{
> + struct device *dev;
> +
> + dev = class_find_device(fpga_bridge_class, NULL, np,
> + fpga_bridge_of_node_match);
> + if (!dev)
> + return ERR_PTR(-ENODEV);
> +
> + return __fpga_bridge_get(dev, info);
> +}
> EXPORT_SYMBOL_GPL(of_fpga_bridge_get);
>
> +static int fpga_bridge_dev_match(struct device *dev, const void *data)
> +{
> + return dev->parent == data;
> +}
> +
> +/**
> + * fpga_bridge_get - get an exclusive reference to a fpga bridge
> + * @dev: parent device that fpga bridge was registered with
> + *
> + * Given a device, get an exclusive reference to a fpga bridge.
> + *
> + * Return: fpga manager struct or IS_ERR() condition containing error code.
> + */
> +struct fpga_bridge *fpga_bridge_get(struct device *dev,
> + struct fpga_image_info *info)
> +{
> + struct device *bridge_dev;
> +
> + bridge_dev = class_find_device(fpga_bridge_class, NULL, dev,
> + fpga_bridge_dev_match);
> + if (!bridge_dev)
> + return ERR_PTR(-ENODEV);
> +
> + return __fpga_bridge_get(bridge_dev, info);
> +}
> +EXPORT_SYMBOL_GPL(fpga_bridge_get);
> +
> /**
> * fpga_bridge_put - release a reference to a bridge
> *
> @@ -206,7 +240,7 @@ void fpga_bridges_put(struct list_head *bridge_list)
> EXPORT_SYMBOL_GPL(fpga_bridges_put);
>
> /**
> - * fpga_bridges_get_to_list - get a bridge, add it to a list
> + * of_fpga_bridge_get_to_list - get a bridge, add it to a list
> *
> * @np: node pointer of a FPGA bridge
> * @info: fpga image specific information
> @@ -216,14 +250,44 @@ EXPORT_SYMBOL_GPL(fpga_bridges_put);
> *
> * Return 0 for success, error code from of_fpga_bridge_get() othewise.
> */
> -int fpga_bridge_get_to_list(struct device_node *np,
> +int of_fpga_bridge_get_to_list(struct device_node *np,
> + struct fpga_image_info *info,
> + struct list_head *bridge_list)
> +{
> + struct fpga_bridge *bridge;
> + unsigned long flags;
> +
> + bridge = of_fpga_bridge_get(np, info);
> + if (IS_ERR(bridge))
> + return PTR_ERR(bridge);
> +
> + spin_lock_irqsave(&bridge_list_lock, flags);
> + list_add(&bridge->node, bridge_list);
> + spin_unlock_irqrestore(&bridge_list_lock, flags);

I know this is not new code, but I was wondering the other day:

Why are we using a single spinlock to protect all lists that are being
passed in as parameters here?

I have a patch that moves the spinlock into the region containing the
list that uses the bridges which (unless I misunderstand something
here), makes more sense:

diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
index 9651aa56244a..b03ec59448e2 100644
--- a/drivers/fpga/fpga-bridge.c
+++ b/drivers/fpga/fpga-bridge.c
@@ -214,6 +214,8 @@ EXPORT_SYMBOL_GPL(fpga_bridges_put);
*
* Get an exclusive reference to the bridge and and it to the list.
*
+ * Must be called with list lock held.
+ *
* Return 0 for success, error code from of_fpga_bridge_get() othewise.
*/
int fpga_bridge_get_to_list(struct device_node *np,
@@ -221,15 +223,12 @@ int fpga_bridge_get_to_list(struct device_node *np,
struct list_head *bridge_list)
{
struct fpga_bridge *bridge;
- unsigned long flags;

bridge = of_fpga_bridge_get(np, info);
if (IS_ERR(bridge))
return PTR_ERR(bridge);

- spin_lock_irqsave(&bridge_list_lock, flags);
list_add(&bridge->node, bridge_list);
- spin_unlock_irqrestore(&bridge_list_lock, flags);

return 0;
}
diff --git a/drivers/fpga/fpga-region.c b/drivers/fpga/fpga-region.c
index 3b6b2f4182a1..c5c958e0e601 100644
--- a/drivers/fpga/fpga-region.c
+++ b/drivers/fpga/fpga-region.c
@@ -37,6 +37,7 @@ struct fpga_region {
struct device dev;
struct mutex mutex; /* for exclusive reference to region */
struct list_head bridge_list;
+ spinlock_t bridge_list_lock; /* protects access to bridge list */
struct fpga_image_info *info;
};

@@ -180,11 +181,15 @@ static int fpga_region_get_bridges(struct fpga_region *region,
struct device *dev = &region->dev;
struct device_node *region_np = dev->of_node;
struct device_node *br, *np, *parent_br = NULL;
+ unsigned long flags;
int i, ret;

/* If parent is a bridge, add to list */
+ spin_lock_irqsave(&region->bridge_list_lock, flags);
ret = fpga_bridge_get_to_list(region_np->parent, region->info,
&region->bridge_list);
+ spin_unlock_irqrestore(&region->bridge_list_lock, flags);
+
if (ret == -EBUSY)
return ret;

@@ -508,6 +513,7 @@ static int fpga_region_probe(struct platform_device *pdev)

mutex_init(&region->mutex);
INIT_LIST_HEAD(&region->bridge_list);
+ spin_lock_init(&region->bridge_list_lock);

device_initialize(&region->dev);
region->dev.class = fpga_region_class;

Am I missing something here? If not I"ll send out my patch separately.


> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_fpga_bridge_get_to_list);
> +
> +/**
> + * fpga_bridge_get_to_list - given device, get a bridge, add it to a list
> + *
> + * @dev: FPGA bridge device
> + * @info: fpga image specific information
> + * @bridge_list: list of FPGA bridges
> + *
> + * Get an exclusive reference to the bridge and and it to the list.
> + *
> + * Return 0 for success, error code from fpga_bridge_get() othewise.
> + */
> +int fpga_bridge_get_to_list(struct device *dev,
> struct fpga_image_info *info,
> struct list_head *bridge_list)
> {
> struct fpga_bridge *bridge;
> unsigned long flags;
>
> - bridge = of_fpga_bridge_get(np, info);
> + bridge = fpga_bridge_get(dev, info);
> if (IS_ERR(bridge))
> return PTR_ERR(bridge);
>
> @@ -381,7 +445,7 @@ static void __exit fpga_bridge_dev_exit(void)
> }
>
> MODULE_DESCRIPTION("FPGA Bridge Driver");
> -MODULE_AUTHOR("Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>");
> +MODULE_AUTHOR("Alan Tull <atull@xxxxxxxxxx>");
> MODULE_LICENSE("GPL v2");
>
> subsys_initcall(fpga_bridge_dev_init);
> diff --git a/drivers/fpga/fpga-region.c b/drivers/fpga/fpga-region.c
> index d9ab7c7..91755562 100644
> --- a/drivers/fpga/fpga-region.c
> +++ b/drivers/fpga/fpga-region.c
> @@ -183,11 +183,14 @@ static int fpga_region_get_bridges(struct fpga_region *region,
> int i, ret;
>
> /* If parent is a bridge, add to list */
> - ret = fpga_bridge_get_to_list(region_np->parent, region->info,
> - &region->bridge_list);
> + ret = of_fpga_bridge_get_to_list(region_np->parent, region->info,
> + &region->bridge_list);
> +
> + /* -EBUSY means parent is a bridge that is under use. Give up. */
> if (ret == -EBUSY)
> return ret;
>
> + /* Zero return code means parent was a bridge and was added to list. */
> if (!ret)
> parent_br = region_np->parent;
>
> @@ -207,8 +210,8 @@ static int fpga_region_get_bridges(struct fpga_region *region,
> continue;
>
> /* If node is a bridge, get it and add to list */
> - ret = fpga_bridge_get_to_list(br, region->info,
> - &region->bridge_list);
> + ret = of_fpga_bridge_get_to_list(br, region->info,
> + &region->bridge_list);
>
> /* If any of the bridges are in use, give up */
> if (ret == -EBUSY) {
> diff --git a/include/linux/fpga/fpga-bridge.h b/include/linux/fpga/fpga-bridge.h
> index dba6e3c..9f6696b 100644
> --- a/include/linux/fpga/fpga-bridge.h
> +++ b/include/linux/fpga/fpga-bridge.h
> @@ -42,6 +42,8 @@ struct fpga_bridge {
>
> struct fpga_bridge *of_fpga_bridge_get(struct device_node *node,
> struct fpga_image_info *info);
> +struct fpga_bridge *fpga_bridge_get(struct device *dev,
> + struct fpga_image_info *info);
> void fpga_bridge_put(struct fpga_bridge *bridge);
> int fpga_bridge_enable(struct fpga_bridge *bridge);
> int fpga_bridge_disable(struct fpga_bridge *bridge);
> @@ -49,9 +51,12 @@ int fpga_bridge_disable(struct fpga_bridge *bridge);
> int fpga_bridges_enable(struct list_head *bridge_list);
> int fpga_bridges_disable(struct list_head *bridge_list);
> void fpga_bridges_put(struct list_head *bridge_list);
> -int fpga_bridge_get_to_list(struct device_node *np,
> +int fpga_bridge_get_to_list(struct device *dev,
> struct fpga_image_info *info,
> struct list_head *bridge_list);
> +int of_fpga_bridge_get_to_list(struct device_node *np,
> + struct fpga_image_info *info,
> + struct list_head *bridge_list);
>
> int fpga_bridge_register(struct device *dev, const char *name,
> const struct fpga_bridge_ops *br_ops, void *priv);
> --
> 2.7.4
>
Thanks,

Moritz

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