linux-kernel - Re: [linux-usb-devel] [RFC] HID bus design overview.

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Date:	Thu, 05 Apr 2007 14:47:19 +0800
From:	Li Yu <raise.sail@...il.com>
To:	Li Yu <raise.sail@...il.com>
CC:	Dmitry Torokhov <dtor@...ightbb.com>, yanghong@...ss.com.cn,
	linux-usb-devel <linux-usb-devel@...ts.sourceforge.net>,
	hongzhiyi@...ss.com.cn, Jiri Kosina <jkosina@...e.cz>,
	Marcel Holtmann <marcel@...tmann.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-usb-devel] [RFC] HID bus design overview.

Dmitry Torokhov wrote:
>>> +int hid_open(struct hid_device *hid)
>>> +{
>>> +	struct hid_transport *tl;
>>> +	int ret;
>>> +
>>> +	if (hid->driver->open)
>>> +		return hid->driver->open(hid);
>>> +	ret = 0;
>>> +	spin_lock(&hid_lock);
>>> +	tl =  hid_transports[hid->bus];
>>> +	if (tl->open)
>>> +		ret = tl->open(hid);
>>> +	spin_unlock(&hid_lock);
>>> +	return ret;
>>> +}
>>>     
>>>       
>> Spinlock is not the best choise here, I'd expect most ->open()
>> implementation wait on some IO.
>>
>>   
>>     
> Yes, I agree! Also, there have another code access hid_transports[]
> without spin it!
>
>   
I think I found out the resolve means for this: using the refcnt of
hid_transport->module,
so we can read access hid_transports[] safely without any lock protection.






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