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From:   Alan Tull <atull@kernel.org>
Date:   Thu, 16 Aug 2018 13:20:39 -0500
Message-ID: <CANk1AXR=Dqv8tAWnUNvSFBjO+8Ccsg4mJSeVH48iejkox7Na2A@mail.gmail.com>
Subject: Re: fpga: fpga_mgr_get() buggy ?
To:     Federico Vaga <federico.vaga@cern.ch>
Cc:     Moritz Fischer <mdf@kernel.org>, linux-fpga@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Thu, Aug 16, 2018 at 2:18 AM, Federico Vaga <federico.vaga@cern.ch> wrote:
> Hi alan,
>
> inline comments
>
> On Wednesday, August 15, 2018 11:02:12 PM CEST Alan Tull wrote:
>> On Wed, Jul 18, 2018 at 4:47 PM, Federico Vaga <federico.vaga@cern.ch>
> wrote:
>> > Hi Alan,
>> >
>> > Thanks for your time, comments below
>> >
>> > On Wednesday, July 18, 2018 9:47:24 PM CEST Alan Tull wrote:
>> >> On Thu, Jun 28, 2018 at 2:50 AM, Federico Vaga <federico.vaga@cern.ch>
>> >
>> > wrote:
>> >> > On Wednesday, 27 June 2018 23:23:07 CEST Alan Tull wrote:
>> >> >> On Wed, Jun 27, 2018 at 4:25 AM, Federico Vaga
>> >> >
>> >> > <federico.vaga@cern.ch> wrote:
>> >> >> > Hi Alan,
>> >> >> >
>> >> >> > On Tuesday, 26 June 2018 23:00:46 CEST Alan Tull wrote:
>> >> >> >> On Fri, Jun 22, 2018 at 2:53 AM, Federico Vaga
>> >> >> >> <federico.vaga@cern.ch> wrote:
>> >> >> >>
>> >> >> >> Hi Federico,
>> >> >> >>
>> >> >> >> >> > What is buggy is the function fpga_mgr_get().
>> >> >> >> >> > That patch has been done to allow multiple FPGA manager
>> >> >> >> >> > instances
>> >> >> >> >> > to be linked to the same device (PCI it says). But function
>> >> >> >> >> > fpga_mgr_get() will return only the first found: what about
>> >> >> >> >> > the
>> >> >> >> >> > others?
>> >>
>> >> Looking at this further, no code change is needed in the FPGA API to
>> >> support multiple managers.  A FPGA manager driver is a self-contained
>> >> platform driver.  The PCI driver for a board that contains multiple
>> >> FPGAs should create a platform device for each manager and save each
>> >> of those devs in its pdata.
>> >>
>> >> >> >> >> > Then, all load kernel-doc comments says:
>> >> >> >> >> >
>> >> >> >> >> > "This code assumes the caller got the mgr pointer from
>> >> >> >> >> > of_fpga_mgr_get() or fpga_mgr_get()"
>> >> >> >> >> >
>> >> >> >> >> > but that function does not allow me to get, for instance,
>> >> >> >> >> > the
>> >> >> >> >> > second FPGA manager on my card.
>> >>
>> >> fpga_mgr_get() will do what you want if your PCI driver creates a
>> >> platform device per FPGA manager as mentioned above.
>> >>
>> >> >> >> >> > Since, thanks to this patch I'm actually the creator of the
>> >> >> >> >> > fpga_manager structure,  I do not need to use fpga_mgr_get()
>> >> >> >> >> > to
>> >> >> >> >> > retrieve that data structure.
>> >>
>> >> The creator of the FPGA mgr structure is the low level FPGA manager
>> >> driver, not the PCIe driver.
>> >
>> > In my case it is.
>> > It's a bit like where SPI driver is the low level FPGA manager driver for
>> > the xilinx-spi.c. But if I understand what you mean, I should always have
>> > a
>> > platform_driver just for the FPGA manager even if it has a 1:1 relation
>> > with its carrier? In other words, I write two drivers:
>> > - one for the FPGA manager
>> > - one for the PCI device that then register the FPGA manager driver
>> >
>> > In my case the FPGA programmed is also the PCIe bridge (GN4124). Probably
>> > I
>> > can do it anyway, because the part dedicated to FPGA programming is quite
>> > independent from the rest (don't remember all details)
>> >
>> >> >> >> >> > Despite this, I believe we still need to increment the
>> >> >> >> >> > module
>> >> >> >> >> > reference counter (which is done by fpga_mgr_get()).
>> >>
>> >> This is only done in the probe function of a FPGA region driver.
>> >>
>> >> >> >> >> > We can fix this function by just replacing the argument from
>> >> >> >> >> > 'device' to 'fpga_manager' (the one returned by create() ).
>> >> >> >> >>
>> >> >> >> >> At first thought, that's what I'd want.
>> >> >> >> >>
>> >> >> >> >> > Alternatively, we
>> >> >> >> >> > can add an 'owner' field in "struct fpga_manager_ops" and
>> >> >> >> >> > 'get'
>> >> >> >> >> > it
>> >> >> >> >> > when we use it. Or again, just an 'owner' argument in the
>> >> >> >> >> > create()
>> >> >> >> >> > function.
>> >> >> >> >>
>> >> >> >> >> It seems like we shouldn't have to do that.
>> >> >> >> >
>> >> >> >> > Why?
>> >> >> >>
>> >> >> >> OK yes, I agree; the kernel has a lot of examples of doing this.
>> >> >> >>
>> >> >> >> I'll have to play with it, I'll probably add the owner arg to the
>> >> >> >> create function, add owner to struct fpga_manager, and save.
>> >> >> >
>> >> >> > I have two though about this.
>> >> >> >
>> >> >> > 1. file_operation like approach. The onwer is associated to the
>> >> >> > FPGA manager operation. Whenever the FPGA manager wants to use an
>> >> >> > operation it get/put the module owner of these operations
>> >> >> > (because this is what we need to protect). With this the user is
>> >> >> > not directly involved, read it as less code, less things to care
>> >> >> > about. And probably there is no need for fpga_manager_get().
>> >> >>
>> >> >> How does try_module_get fit into this scheme?  I think this proposal
>> >> >> #1 is missing the point of what the reference count increment is
>> >> >> meant to do.  Or am I misunderstanding?  How does that keep the
>> >> >> module from being unloaded 1/3 way through programming a FPGA?
>> >> >> IIUC you are saying that the reference count would be incremented
>> >> >> before doing the manager ops .write_init, then decremented again
>> >> >> afterwards, incremented before each call to .write, decremented
>> >> >> afterwards, then the same for .write_complete.
>> >> >
>> >> > I'm not saying to do module_get/put just around the mops->XXX(): it's
>> >> > too much. Just where you have this comment:
>> >> >
>> >> > "This code assumes the caller got the mgr pointer from
>> >> > of_fpga_mgr_get() or fpga_mgr_get()"
>> >> >
>> >> > Because, currently, it's here where we do module_get()
>> >>
>> >> No it's not.
>> >
>> > It is not in the code, but the comment says that we should do it before
>> > calling fpga_mgr_load()
>> >
>> >> fpga_mgr_get() or of_fpga_mgr_get() is called when the region is
>> >> created such as in of-fpga-region's probe.  That way, as long as the
>> >> region exists, the manager won't be unloaded.  If someone wants to
>> >> start unloading modules, they need to unload higher level ones first,
>> >> so they'll have to unload the region before mgr.
>> >>
>> >> > Most mops are invoked within a set of static functions which are
>> >> > called only by few exported functions. I'm suggesting to do
>> >> > module_get/put in those exported function at the beginning (get) and
>> >> > and the end (put) because we know that within these functions, here
>> >> > and there, we will use mops which are owned by a different module.
>> >> > We do not want the module owner of the mops to disappear while someone
>> >> > is doing fpga_mgr_load(). For example, inside fpga_mgr_load() we use
>> >> > most of the mops, so we 'get' the module at the beginning and 'put' it
>> >> > at the end. The same for fpga_region_program_fpga().
>> >>
>> >> If we do it the way you are suggesting, then someone can unload the
>> >> manager module without unloading the region.  The region code will be
>> >> in for a nasty surprise when programming is attempted.
>> >
>> > Of course, this should be taken into account. I was not suggesting a
>> > precise implementation, but only the idea to hide get/put. Probably there
>> > other things as well that I'm not considering (indeed I do not have a
>> > patch, but just a comment)
>> >
>> >> > Like this we do not have to ask users to do fpga_mgr_get()/put().
>> >>
>> >> The only user who has to do this is a region's probe function.
>> >>
>> >> I'm assuming that only fpga_region is using fpga_mgr_load() and
>> >> anybody who is creating a region uses fpga_region_program_fpga().
>> >> That's what I want to encourage anyway.  I should probably move
>> >> fpga_mgr_load to a private header.
>> >
>> > All right, if this is what you want to encourage I do not have anything to
>> > say because I did exactly what you do not want to encourage :)
>> >
>> > For me this change everything because I do not use regions since I do not
>> > have them. The way the API is exposed to me did not encouraged me to use
>> > their API. In addition, the documentation guides me directly to the FPGA
>> > manager.
>>
>> The documentation says:
>>
>> "If you are adding a new interface to the FPGA framework, add it on
>> top of a FPGA region to allow the most reuse of your interface."
>
> I would change this in something like:
>
> "If you are adding a new interface to the FPGA framework, add it on
> top of a FPGA region."

Sure, will do in v2.

>
> What I understand from the current statement is:
> "if you care about re-usability, add your interface on top of an FPGA region"
> Since in my special case, I do not care about re-usability, I skipped the FPGA
> region.

OK yeah, not what I'm trying to communicate.  Good feedback.

>
>> https://www.kernel.org/doc/html/latest/driver-api/fpga/intro.html
>>
>> But the stuff that I submitted yesterday goes back through the docs to
>> clear out anything that is not clear about this.
>>
>> > To be honest I did not have much time to look at the region code. My
>> > understanding, after a quick look, is that it works great with
>> > device-tree.
>>
>> It is used by the DFL framework which doesn't use device tree.
>>
>> > But what if I do not have it? Actually, I cannot use device-tree because
>> > of
>> > environment limitations and Linux version in use. Oops, this implies that
>> > I
>> > back-ported the FPGA manager to an older Linux version? Yes, guilty :)
>>
>> I separated region code from its device-tree dependencies.  But if you
>> can't use device-tree, then you end up having to implement some of the
>> things DT gives you for free.
>
> unfortunately yes
>
>> > Anyway, I'm using the API exposed, and if part of the assumptions behind
>> > this API is that I should use device-tree, then I'm out of scope.
>> >
>> > <chatting>
>> > Just for chatting. One addition I made for the FPGA manager is to support
>> >
>> > dynamic loading of FPGA code using char devices. Something like:
>> >    dd if=binary.bin of=/dev/fpga0
>> >    cat binary.bin > /dev/fpga0
>>
>> Since it's not handling the bridge, there's some risk involved.
>>
>> > We do not have device tree, and we do not have binaries in /lib/firmware.
>> > It's quite handy to quickly load a binary just synthesized, especially for
>> > debugging purpose.
>>
>> Like a debugfs?
>>
>> https://lkml.org/lkml/2018/8/2/125
>>
>> But for a debugging/developing, I have a debugfs that was a downstream
>> patchset that I'm cleaning for submission.
>
> Yes, like that more or less.
>
> I did a chardevice in /dev/ because in our environment debugfs is not mounted
> automatically and we need this feature also operationally. But yes, that's the
> idea.
>
> One comment. The code on github [1] looks like it is assuming that on
> userspace people write the full image in one shot and it is smaller that 4MiB.
> What I did is to build a scatterlist in order to support the following case:
>
> cat image.bin > /sys/kernel/debug/.../image
>
> where `cat` write 4K at time. And it can be bigger than 4M
>
> [1] https://github.com/altera-opensource/linux-socfpga/blob/socfpga-4.17/
> drivers/fpga/fpga-mgr-debugfs.c

I squashed these patches, cleaned up a bit and posted them yesterday.

> Below (end of this email) the patch I quickly did last year. Unfortunately I
> do not have the time to clean this solution, so it is the very first thing I
> implemented without many thoughts (that's why I never pushed this patch).

Your scatter-gather code is much nicer that my debugfs code that needs
the image to be written in one big chunk to be copied.

>
>
>> > If you are interested I can try to clean it up (at some
>> > point, probably in autumn), or I can show you the code in private for a
>> > quick look.
>> > </chatting>
>> >
>> >> > <Parenthesis>
>> >> > fpga_region_program_fpga() does not do (today) fpga_mgr_get() because
>> >> > it assumes, but it is not enforced, that both fpga_region and fpga_mgr
>> >> > are child of the same device.
>> >>
>> >> fpga_region_program_fpga() doesn't do fpga_mgr_get() becuase
>> >> fpga_mgr_get() happens when the fpga_region probes.  The assumption I
>> >> am making is that nobody other than a region is calling
>> >> fpga_manager_load().  I should create a fpga_private.h and move
>> >> fpga_manager_load() out of fpga-mgr.h to make that official.
>> >
>> > Yes, I agree. If what I'm doing is not supposed to happen I should not be
>> > allowed to do it :)
>> >
>> > <suggestion>
>> > If you want to encourage people to use regions rather than the manager
>> > directly, have you though about changing the API and merge in a single
>> > module fpga-mgr and fpga-region?
>> >
>> > Brainstorming. Perhaps, it is possible to have a `struct fpga_region_info`
>> > and when we register and FPGA manager we use something like:
>> >
>> > struct fpga_manager *fpga_mgr_create(struct device *dev, const char *name,
>> >
>> >                                      const struct fpga_manager_ops *mops,
>> >
>> >                      struct fpga_region_info *info, int n_regions,
>> >
>> >                                      void *priv)
>> >
>> > So those regions will be created directly and the interface will be
>> > smaller
>> > and easier.
>> >
>> > Don't waste much time on this suggestion, as I said before I did not study
>> > much the fpga-region.c code and perhaps this is not possible and I'm just
>> > speaking rubbish :)
>> > </suggestion>
>> >
>> >> > Probably this is true 99.99% of the
>> >> > time.
>> >> > Let me open in parallel another point: why fpga_region is not a child
>> >> > of fpga_manager?
>> >>
>> >> FPGA regions are children of FPGA bridges.
>> >>
>> >> Alan
>> >
>> > --
>> > Federico Vaga
>> > [BE-CO-HT]
>> >
>> >
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-fpga" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
> ------
> From d6a6df9515c5e92cc74b8948c3c10ac9cbeec6d2 Mon Sep 17 00:00:00 2001
> From: Federico Vaga <federico.vaga@vaga.pv.it>
> Date: Mon, 20 Nov 2017 14:40:26 +0100
> Subject: [PATCH] fpga: program from user-space
>
> Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
> ---
>  Documentation/fpga/fpga-mgr.txt |   3 +
>  drivers/fpga/fpga-mgr.c         | 261 ++++++++++++++++++++++++++++++++++++++
> +-
>  include/linux/fpga/fpga-mgr.h   |  19 +++
>  3 files changed, 281 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/fpga/fpga-mgr.txt b/Documentation/fpga/fpga-mgr.txt
> index 78f197f..397dae9 100644
> --- a/Documentation/fpga/fpga-mgr.txt
> +++ b/Documentation/fpga/fpga-mgr.txt
> @@ -197,3 +197,6 @@ to put the FPGA into operating mode.
>  The ops include a .state function which will read the hardware FPGA manager
> and
>  return a code of type enum fpga_mgr_states.  It doesn't result in a change in
>  hardware state.
> +
> +Configuring the FPGA from user-space
> +====================================
> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
> index 6441f91..964b7e4 100644
> --- a/drivers/fpga/fpga-mgr.c
> +++ b/drivers/fpga/fpga-mgr.c
> @@ -27,10 +27,56 @@
>  #include <linux/slab.h>
>  #include <linux/scatterlist.h>
>  #include <linux/highmem.h>
> +#include <linux/spinlock.h>
>  #include <linux/version.h>
> +#include <linux/cdev.h>
> +#include <linux/list.h>
>
>  static DEFINE_IDA(fpga_mgr_ida);
>  static struct class *fpga_mgr_class;
> +static dev_t fpga_mgr_devt;
> +
> +/**
> + * struct fpga_image_chunck - FPGA configuration chunck
> + * @data: chunk data
> + * @size: chunk data size
> + * @list: for the linked list of chunks
> + */
> +struct fpga_image_chunk {
> +       void *data;
> +       size_t size;
> +       struct list_head list;
> +};
> +#define CHUNK_MAX_SIZE (PAGE_SIZE)
> +
> +/**
> + * struct fpga_user_load - structure to handle configuration from user-space
> + * @mgr: pointer to the FPGA manager
> + * @chunk_list: HEAD point of a linked list of FPGA chunks
> + * @n_chunks: number of chunks in the list
> + * @lock: it protects: chunk_list, n_chunks
> + */
> +struct fpga_user_load {
> +       struct fpga_manager *mgr;
> +       struct list_head chunk_list;
> +       unsigned int n_chunks;
> +       struct spinlock lock;
> +};
> +
> +
> +/**
> + * It sets by default a huge timeout for configuration coming from user-space
> + * just to play safe.
> + *
> + * FIXME what about sysfs parameters to adjust it? The flag bit in particular
> + */
> +struct fpga_image_info default_user_info = {
> +       .flags = 0,
> +       .enable_timeout_us = 10000000, /* 10s */
> +       .disable_timeout_us = 10000000, /* 10s */
> +       .config_complete_timeout_us = 10000000, /* 10s */
> +};
> +
>
>  /*
>   * Call the low level driver's write_init function.  This will do the
> @@ -310,6 +356,158 @@ int fpga_mgr_firmware_load(struct fpga_manager *mgr,
>  }
>  EXPORT_SYMBOL_GPL(fpga_mgr_firmware_load);
>
> +
> +static int fpga_mgr_open(struct inode *inode, struct file *file)
> +{
> +       struct fpga_manager *mgr = container_of(inode->i_cdev,
> +                                               struct fpga_manager,
> +                                               cdev);
> +       struct fpga_user_load *usr;
> +       int ret;
> +
> +       /* Allow the user-space programming only if user unlocked the FPGA */
> +       if (!test_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags)) {
> +               dev_info(&mgr->dev, "The FPGA programming is locked\n");
> +               return -EPERM;
> +       }
> +
> +       ret = mutex_trylock(&mgr->usr_mutex);
> +       if (ret == 0)
> +               return -EBUSY;
> +
> +       usr = kzalloc(sizeof(struct fpga_user_load), GFP_KERNEL);
> +       if (!usr) {
> +               ret = -ENOMEM;
> +               goto err_alloc;
> +       }
> +
> +       usr->mgr = mgr;
> +       spin_lock_init(&usr->lock);
> +       INIT_LIST_HEAD(&usr->chunk_list);
> +       file->private_data = usr;
> +
> +       return 0;
> +
> +err_alloc:
> +       spin_lock(&mgr->lock);
> +       clear_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags);
> +       spin_unlock(&mgr->lock);
> +       mutex_unlock(&mgr->usr_mutex);
> +       return ret;
> +}
> +
> +
> +static int fpga_mgr_flush(struct file *file, fl_owner_t id)
> +{
> +       struct fpga_user_load *usr = file->private_data;
> +       struct fpga_image_chunk *chunk, *tmp;
> +       struct sg_table sgt;
> +       struct scatterlist *sg;
> +       int err = 0;
> +
> +       if (!usr->n_chunks)
> +               return 0;
> +
> +       err = sg_alloc_table(&sgt, usr->n_chunks, GFP_KERNEL);
> +       if (err)
> +               goto out;
> +
> +       sg = sgt.sgl;
> +       list_for_each_entry(chunk, &usr->chunk_list, list) {
> +               sg_set_buf(sg, chunk->data, chunk->size);
> +               sg = sg_next(sg);
> +               if (!sg)
> +                       break;
> +       }
> +
> +       err = fpga_mgr_buf_load_sg(usr->mgr,
> +                                  &default_user_info,
> +                                  &sgt);
> +       sg_free_table(&sgt);
> +
> +out:
> +       /* Remove all chunks */
> +       spin_lock(&usr->lock);
> +       list_for_each_entry_safe(chunk, tmp, &usr->chunk_list, list) {
> +               list_del(&chunk->list);
> +               kfree(chunk->data);
> +               kfree(chunk);
> +               usr->n_chunks--;
> +       }
> +       spin_unlock(&usr->lock);
> +
> +       return err;
> +}
> +
> +
> +static int fpga_mgr_close(struct inode *inode, struct file *file)
> +{
> +       struct fpga_user_load *usr = file->private_data;
> +       struct fpga_manager *mgr = usr->mgr;
> +
> +       kfree(usr);
> +
> +       spin_lock(&mgr->lock);
> +       clear_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags);
> +       spin_unlock(&mgr->lock);
> +
> +       mutex_unlock(&mgr->usr_mutex);
> +
> +       return 0;
> +}
> +
> +
> +static ssize_t fpga_mgr_write(struct file *file, const char __user *buf,
> +                             size_t count, loff_t *offp)
> +{
> +       struct fpga_user_load *usr = file->private_data;
> +       struct fpga_image_chunk *chunk;
> +       int err;
> +
> +       chunk = kmalloc(sizeof(struct fpga_image_chunk), GFP_KERNEL);
> +       if (!chunk)
> +               return -ENOMEM;
> +
> +       chunk->size = count > CHUNK_MAX_SIZE ? CHUNK_MAX_SIZE : count;
> +       chunk->data = kmalloc(chunk->size, GFP_KERNEL);
> +       if (!chunk->data) {
> +               err = -ENOMEM;
> +               goto err_buf_alloc;
> +       }
> +
> +       err = copy_from_user(chunk->data, buf, chunk->size);
> +       if(err)
> +               goto err_buf_copy;
> +
> +       spin_lock(&usr->lock);
> +       list_add_tail(&chunk->list, &usr->chunk_list);
> +       usr->n_chunks++;
> +       spin_unlock(&usr->lock);
> +
> +       *offp += count;
> +
> +       return chunk->size;
> +
> +err_buf_copy:
> +       kfree(chunk->data);
> +err_buf_alloc:
> +       kfree(chunk);
> +       return err;
> +}
> +
> +
> +/**
> + * Char device operation
> + */
> +static const struct file_operations fpga_mgr_fops = {
> +       .owner = THIS_MODULE,
> +       .open = fpga_mgr_open,
> +       .flush = fpga_mgr_flush,
> +       .release = fpga_mgr_close,
> +       .write  = fpga_mgr_write,
> +};
> +
> +
>  static const char * const state_str[] = {
>         [FPGA_MGR_STATE_UNKNOWN] =              "unknown",
>         [FPGA_MGR_STATE_POWER_OFF] =            "power off",
> @@ -352,13 +550,43 @@ static ssize_t state_show(struct device *dev,
>         return sprintf(buf, "%s\n", state_str[mgr->state]);
>  }
>
> +static ssize_t config_lock_show(struct device *dev,
> +                               struct device_attribute *attr, char *buf)
> +{
> +       struct fpga_manager *mgr = to_fpga_manager(dev);
> +
> +       if (test_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags))
> +               return sprintf(buf, "unlock\n");
> +       return sprintf(buf, "lock\n");
> +}
> +
> +static ssize_t config_lock_store(struct device *dev,
> +                                struct device_attribute *attr,
> +                                const char *buf, size_t count)
> +{
> +       struct fpga_manager *mgr = to_fpga_manager(dev);
> +
> +       spin_lock(&mgr->lock);
> +       if (strncmp(buf, "lock" , min(4, (int)count)) == 0)
> +               clear_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags);
> +       else if (strncmp(buf, "unlock" , min(6, (int)count)) == 0)
> +               set_bit(FPGA_MGR_FLAG_UNLOCK, mgr->flags);
> +       else
> +               count = -EINVAL;
> +       spin_unlock(&mgr->lock);
> +
> +       return count;
> +}
> +
>  #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,11,0)
>  static DEVICE_ATTR_RO(name);
>  static DEVICE_ATTR_RO(state);
> +static DEVICE_ATTR_RW(config_lock);
>
>  static struct attribute *fpga_mgr_attrs[] = {
>         &dev_attr_name.attr,
>         &dev_attr_state.attr,
> +       &dev_attr_lock.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(fpga_mgr);
> @@ -367,6 +595,9 @@ ATTRIBUTE_GROUPS(fpga_mgr);
>  static struct device_attribute fpga_mgr_attrs[] = {
>         __ATTR(name, S_IRUGO, name_show, NULL),
>         __ATTR(state, S_IRUGO, state_show, NULL),
> +       __ATTR(config_lock, S_IRUGO | S_IWUSR | S_IRGRP | S_IWGRP,
> +              config_lock_show, config_lock_store),
> +       __ATTR_NULL,
>  };
>  #endif
>
> @@ -507,6 +738,8 @@ int fpga_mgr_register(struct device *dev, const char
> *name,
>         }
>
>         mutex_init(&mgr->ref_mutex);
> +       mutex_init(&mgr->usr_mutex);
> +       spin_lock_init(&mgr->lock);
>
>         mgr->name = name;
>         mgr->mops = mops;
> @@ -524,12 +757,19 @@ int fpga_mgr_register(struct device *dev, const char
> *name,
>         mgr->dev.parent = dev;
>         mgr->dev.of_node = dev->of_node;
>         mgr->dev.id = id;
> +       mgr->dev.devt = MKDEV(MAJOR(fpga_mgr_devt), id);
>         dev_set_drvdata(dev, mgr);
>
>         ret = dev_set_name(&mgr->dev, "fpga%d", id);
>         if (ret)
>                 goto error_device;
>
> +       cdev_init(&mgr->cdev, &fpga_mgr_fops);
> +       mgr->cdev.owner = THIS_MODULE;
> +       ret = cdev_add(&mgr->cdev, mgr->dev.devt, 1);
> +       if (ret)
> +               goto err_cdev;
> +
>         ret = device_add(&mgr->dev);
>         if (ret)
>                 goto error_device;
> @@ -539,6 +779,8 @@ int fpga_mgr_register(struct device *dev, const char
> *name,
>         return 0;
>
>  error_device:
> +       cdev_del(&mgr->cdev);
> +err_cdev:
>         ida_simple_remove(&fpga_mgr_ida, id);
>  error_kfree:
>         kfree(mgr);
> @@ -572,17 +814,27 @@ static void fpga_mgr_dev_release(struct device *dev)
>  {
>         struct fpga_manager *mgr = to_fpga_manager(dev);
>
> +       cdev_del(&mgr->cdev);
>         ida_simple_remove(&fpga_mgr_ida, mgr->dev.id);
>         kfree(mgr);
>  }
>
>  static int __init fpga_mgr_class_init(void)
>  {
> +       int err;
> +
>         pr_info("FPGA manager framework\n");
>
> +       err = alloc_chrdev_region(&fpga_mgr_devt, 0, FPGA_MGR_MAX_DEV,
> +                                 "fpga_mgr");
> +       if (err)
> +               return err;
> +
>         fpga_mgr_class = class_create(THIS_MODULE, "fpga_manager");
> -       if (IS_ERR(fpga_mgr_class))
> -               return PTR_ERR(fpga_mgr_class);
> +       if (IS_ERR(fpga_mgr_class)) {
> +               err = PTR_ERR(fpga_mgr_class);
> +               goto err_class;
> +       }
>  #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,11,0)
>         fpga_mgr_class->dev_groups = fpga_mgr_groups;
>  #else
> @@ -591,12 +843,17 @@ static int __init fpga_mgr_class_init(void)
>         fpga_mgr_class->dev_release = fpga_mgr_dev_release;
>
>         return 0;
> +
> +err_class:
> +       unregister_chrdev_region(fpga_mgr_devt, FPGA_MGR_MAX_DEV);
> +       return err;
>  }
>
>  static void __exit fpga_mgr_class_exit(void)
>  {
>         class_destroy(fpga_mgr_class);
>         ida_destroy(&fpga_mgr_ida);
> +       unregister_chrdev_region(fpga_mgr_devt, FPGA_MGR_MAX_DEV);
>  }
>
>  MODULE_AUTHOR("Alan Tull <atull@opensource.altera.com>");
> diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
> index bfa14bc..ae38e48 100644
> --- a/include/linux/fpga/fpga-mgr.h
> +++ b/include/linux/fpga/fpga-mgr.h
> @@ -15,8 +15,10 @@
>   * You should have received a copy of the GNU General Public License along
> with
>   * this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
> +#include <linux/cdev.h>
>  #include <linux/mutex.h>
>  #include <linux/platform_device.h>
> +#include <linux/spinlock.h>
>
>  #ifndef _LINUX_FPGA_MGR_H
>  #define _LINUX_FPGA_MGR_H
> @@ -24,6 +26,8 @@
>  struct fpga_manager;
>  struct sg_table;
>
> +#define FPGA_MGR_MAX_DEV (256)
> +
>  /**
>   * enum fpga_mgr_states - fpga framework states
>   * @FPGA_MGR_STATE_UNKNOWN: can't determine state
> @@ -118,22 +122,37 @@ struct fpga_manager_ops {
>         void (*fpga_remove)(struct fpga_manager *mgr);
>  };
>
> +/*
> + * List of status FLAGS for the FPGA manager
> + */
> +#define FPGA_MGR_FLAG_BITS (32)
> +#define FPGA_MGR_FLAG_UNLOCK BIT(0)
> +
>  /**
>   * struct fpga_manager - fpga manager structure
>   * @name: name of low level fpga manager
> + * @cdev: char device interface
>   * @dev: fpga manager device
>   * @ref_mutex: only allows one reference to fpga manager
>   * @state: state of fpga manager
>   * @mops: pointer to struct of fpga manager ops
>   * @priv: low level driver private date
> + * @flags: manager status bits
> + * @lock: it protects: flags
> + * @usr_mutex: only allows one user to program the FPGA
>   */
>  struct fpga_manager {
>         const char *name;
> +       struct cdev cdev;
>         struct device dev;
>         struct mutex ref_mutex;
>         enum fpga_mgr_states state;
>         const struct fpga_manager_ops *mops;
>         void *priv;
> +
> +       DECLARE_BITMAP(flags, FPGA_MGR_FLAG_BITS);
> +       struct spinlock lock;
> +       struct mutex usr_mutex;
>  };
>
>  #define to_fpga_manager(d) container_of(d, struct fpga_manager, dev)
> --
> 2.15.0
>
>
>
>
>