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

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Date:	Fri, 11 Dec 2009 10:05:06 +0800
From:	Barry Song <21cnbao@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	vapier.adi@...il.com, 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

2009/12/11 David Miller <davem@...emloft.net>:
> From: Mike Frysinger <vapier.adi@...il.com>
> Date: Thu, 10 Dec 2009 05:58:58 -0500
>
>> 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?

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