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 12:00:34 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Mike Frysinger <vapier.adi@...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 Fri, Dec 11, 2009 at 10:17 AM, Mike Frysinger <vapier.adi@...il.com> wrote:
> 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

Wolfgang/David, are you ok with that too? If so, I will send a -v4
patch using bfin_read/write, with all fix according to your other
comments.

> -mike
>
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