Message-ID: <20170918175927.GA3429@tyrael.ni.corp.natinst.com>
Date:   Mon, 18 Sep 2017 10:59:27 -0700
From:   Moritz Fischer <mdf@...nel.org>
To:     Alan Tull <atull@...nel.org>
Cc:     Moritz Fischer <mdf@...nel.org>, linux-kernel@...r.kernel.org,
        linux-fpga@...r.kernel.org
Subject: Re: [PATCH v4 01/18] fpga: bridge: support getting bridge from device

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@...nel.org>
> ---
> 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@...nsource.altera.com>");
> +MODULE_AUTHOR("Alan Tull <atull@...nel.org>");
>  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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