linux-kernel - Re: [PATCH 2/2] New driver: Xillybus generic interface for FPGA (programmable logic)

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Message-id: <50BB8F43.4010208@gmail.com>
Date:	Sun, 02 Dec 2012 19:26:27 +0200
From:	Eli Billauer <eli.billauer@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH 2/2] New driver: Xillybus generic interface for FPGA
 (programmable logic)

On 11/30/2012 06:32 PM, Greg KH wrote:
>>>> >  >>+static struct class *xillybus_class;
>>>>          
>>> >  >Why not just use the misc interface instead of your own class?
>>>        
>> >  When Xillybus is used, the whole system's mission is usually around
>> >  it (e.g. it's a computer doing data acquisition through the Xillybus
>> >  pipes). So giving it a high profile makes sense, I believe. Besides,
>> >  a dozen of device files are not rare.
>>      
> It is no problem to create dozens of misc devices.  It makes your driver
> smaller, contain less code that I have to audit and you have to ensure
> you got right, and it removes another user of 'struct class' which we
> are trying to get rid of anyway.  So please, move to use a misc device.
>
>    

It has just occurred to me that DYNAMIC_MINORS is 64 
(drivers/char/misc.c), so I guess that limits the number of misc devices 
that can be generated, at least with dynamically allocated minors. I 
previously mentioned "a dozen" as the number of devices, but I've 
already run tests with 100+ devices, and I can also think of a sane 
application for that.


So if I understood the situation correctly, it looks like using misc 
devices will create a limitation which will be reached sooner or later.

Any suggestion what to do?

Thanks in advance,

     Eli


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