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 05:58:58 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	"H.J. Oertel" <oe@...t.de>, netdev@...r.kernel.org,
	socketcan-core@...ts.berlios.de,
	uclinux-dist-devel@...ckfin.uclinux.org, davem@...emloft.net
Subject: Re: [Uclinux-dist-devel] [PATCH v3] add the driver for Analog Devices 
	Blackfin on-chip CAN controllers

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.  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.
-mike
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