linux-kernel - Re: [PATCH v2 2/2] uacce: add uacce driver

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Message-ID: <5c2b0889-ea05-1ecd-fe5b-40611bd31945@linaro.org>
Date:   Thu, 29 Aug 2019 17:05:13 +0800
From:   zhangfei <zhangfei.gao@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, jonathan.cameron@...wei.com,
        kenneth-lee-2012@...mail.com, Wangzhou <wangzhou1@...ilicon.com>,
        linux-accelerators@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Kenneth Lee <liguozhu@...ilicon.com>,
        Zaibo Xu <xuzaibo@...wei.com>
Subject: Re: [PATCH v2 2/2] uacce: add uacce driver

Hi, Greg

On 2019/8/28 下午11:22, Greg Kroah-Hartman wrote:
> On Wed, Aug 28, 2019 at 09:27:56PM +0800, Zhangfei Gao wrote:
>> +struct uacce {
>> +	const char *drv_name;
>> +	const char *algs;
>> +	const char *api_ver;
>> +	unsigned int flags;
>> +	unsigned long qf_pg_start[UACCE_QFRT_MAX];
>> +	struct uacce_ops *ops;
>> +	struct device *pdev;
>> +	bool is_vf;
>> +	u32 dev_id;
>> +	struct cdev cdev;
>> +	struct device dev;
>> +	void *priv;
>> +	atomic_t state;
>> +	int prot;
>> +	struct mutex q_lock;
>> +	struct list_head qs;
>> +};
> At a quick glance, this problem really stood out to me.  You CAN NOT
> have two different objects within a structure that have different
> lifetime rules and reference counts.  You do that here with both a
> 'struct cdev' and a 'struct device'.  Pick one or the other, but never
> both.
>
> I would recommend using a 'struct device' and then a 'struct cdev *'.
> That way you get the advantage of using the driver model properly, and
> then just adding your char device node pointer to "the side" which
> interacts with this device.
>
> Then you might want to call this "struct uacce_device" :)

Here the 'struct cdev' and 'struct device' have the same lifetime and 
refcount.
They are allocated with uacce when uacce_register and freed when 
uacce_unregister.

To make it clear, how about adding this.

+static void uacce_release(struct device *dev)
+{
+       struct uacce *uacce = UACCE_FROM_CDEV_ATTR(dev);
+
+       idr_remove(&uacce_idr, uacce->dev_id);
+       kfree(uacce);
+}
+
  static int uacce_create_chrdev(struct uacce *uacce)
  {
         int ret;
@@ -819,6 +827,7 @@ static int uacce_create_chrdev(struct uacce *uacce)
         uacce->dev.class = uacce_class;
         uacce->dev.groups = uacce_dev_attr_groups;
         uacce->dev.parent = uacce->pdev;
+       uacce->dev.release = uacce_release;
         dev_set_name(&uacce->dev, "%s-%d", uacce->drv_name, uacce->dev_id);
         ret = cdev_device_add(&uacce->cdev, &uacce->dev);
         if (ret)
@@ -835,7 +844,7 @@ static int uacce_create_chrdev(struct uacce *uacce)
  static void uacce_destroy_chrdev(struct uacce *uacce)
  {
         cdev_device_del(&uacce->cdev, &uacce->dev);
-       idr_remove(&uacce_idr, uacce->dev_id);
+       put_device(&uacce->dev);
  }

  static int uacce_dev_match(struct device *dev, void *data)
@@ -1042,8 +1051,6 @@ void uacce_unregister(struct uacce *uacce)
         uacce_destroy_chrdev(uacce);

         mutex_unlock(&uacce_mutex);
-
-       kfree(uacce);
  }


uacce_destroy_chrdev->put_device(&uacce->dev)->uacce_release->kfree(uacce).

And find there are many examples in driver/
$ grep -rn cdev_device_add drivers/
drivers/rtc/class.c:362:        err = cdev_device_add(&rtc->char_dev, 
&rtc->dev);
rivers/gpio/gpiolib.c:1181:    status = cdev_device_add(&gdev->chrdev, 
&gdev->dev);
drivers/soc/qcom/rmtfs_mem.c:223:       ret = 
cdev_device_add(&rmtfs_mem->cdev, &rmtfs_mem->dev);
drivers/input/joydev.c:989:     error = cdev_device_add(&joydev->cdev, 
&joydev->dev);
drivers/input/mousedev.c:907:   error = cdev_device_add(&mousedev->cdev, 
&mousedev->dev);
drivers/input/evdev.c:1419:     error = cdev_device_add(&evdev->cdev, 
&evdev->dev);

like drivers/input/evdev.c,
evdev is alloced with initialization of dev and cdev,
and evdev is freed in release ops evdev_free
struct evdev {
         struct device dev;
         struct cdev cdev;
         ~
};

Thanks