linux-kernel - Re: Xilinx: hwicap driver comments

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Message-ID: <47AB88AF.7090403@gmail.com>
Date:	Thu, 07 Feb 2008 23:39:43 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Stephen Neuendorffer <stephen.neuendorffer@...inx.com>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Xilinx: hwicap driver comments

On 02/07/2008 11:31 PM, Stephen Neuendorffer wrote:
>> Few comments I have:
>> - release f_op retval is silently ignored, I guess you will get your
> device into
>> undefined state when the first function fails (esp. when you interrupt
> the sem)
> 
> Hmm..  hadn't realized that.  I'm open to suggestions on how to do this
> better.  The real reason why the synchronization is there is to make
> sure that only one client is using the device at a time, using the
> is_open flag.

just mutex_lock(); that need not be interrupted.

>> - semaphores are deprecated
>> - class_device_create is deprecated
> 
> What is preferred?

device_create(); and pass the struct device as a parent when you are at it. 
Otherwise it will be in /sys/*/virtual/* I suppose.

>> - don't understand this:
>>                  memcpy(kbuf, drvdata->read_buffer, bytes_remaining);
>>                  drvdata->read_buffer_in_use = bytes_remaining;
>>                  free_page((unsigned long)kbuf);
> 
> The physical device only generates/accepts complete words, the intention
> is to account for the possibility that a read does not read complete
> words, and to fulfill the read whenever possible.
> It's arguable that read() and write() should not accept or return
> partial words, I suppose

OK, but why are you copying anything to buffer which you free 2 lines below?
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