netdev - Re: [Uclinux-dist-devel] [PATCH v3] add the driver for Analog Devices Blackfin on-chip CAN controllers

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Date:	Thu, 10 Dec 2009 21:17:36 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Barry Song <21cnbao@...il.com>
Cc:	David Miller <davem@...emloft.net>, wg@...ndegger.com, oe@...t.de,
	netdev@...r.kernel.org, socketcan-core@...ts.berlios.de,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [Uclinux-dist-devel] [PATCH v3] add the driver for Analog Devices 
	Blackfin on-chip CAN controllers

On Thu, Dec 10, 2009 at 21:05, Barry Song wrote:
> 2009/12/11 David Miller <davem@...emloft.net>:
>> From: Mike Frysinger <vapier.adi@...il.com>
>>> On Thu, Dec 10, 2009 at 05:48, Wolfgang Grandegger wrote:
>>>> Wolfgang Grandegger wrote:
>>>>> Mike Frysinger wrote:
>>>>>> On Thu, Dec 10, 2009 at 04:11, Wolfgang Grandegger wrote:
>>>>>>> Well, I'm still not a friend of the following inline functions,
>>>>>>> especially the *one-liners* which are called just *once*. With the usage
>>>>>>> of structs they seem even more useless.
>>>>>> seems like it would make more sense to not even use the read/write
>>>>>> functions either. �,A just declare the regs as volatile and assign/read
>>>>>> the struct directly.
>>>>>
>>>>> Two times no. Don't use volatile and proper accessor functions. See:
>>>>>
>>>>> http://lxr.linux.no/#linux+v2.6.32/Documentation/volatile-considered-harmful.txt
>>>>
>>>> I was just wondering if bfin_read/write16 would not be the proper
>>>> accessor functions. readw/writew seems to be implemented differently:
>>>>
>>>> http://lxr.linux.no/#linux+v2.6.32/arch/blackfin/include/asm/io.h#L44
>>>>
>>>> Puh, they do an cli,nop,nop,sync..sti for the access. This also nicely
>>>> shows why accessor functions should be used to access device registers.
>>>>
>>>> Well, just curious. I don't really know the blackfin arch.
>>>
>>> the common I/O functions need to account for issues surrounding the
>>> bus that has arbitrary devices memory mapped to it.  on-chip devices
>>> (like what we're talking about here) do not have these issues and so
>>> using the common functions is awful overhead.
>>
>> Then create special accessors (perhaps with the same names as the
>> existing ones, but with "__" prepended) that lack all of the
>> interrupt disabling, syncs, etc.
>>
>> Really it _is_ cleaner and makes your driver look a lot nicer.
>
> I think Mike has said the functions are bfin_read/bfin_write in
> blackfin arch since those CAN registers are located in memory mapped
> area but not async memory and have less overhead than common io
> functions? Is it acceptable to use those functions in this driver?

yes, bfin_{read,write} should be used
-mike
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