Re: [net-next-2.6 PATCH v2] can: SJA1000: generic OF platform bus driver

[David Miller <davem@davemloft.net>]

From: Arnd Bergmann <arnd@arndb.de>
Date: Tue, 26 May 2009 10:10:30 +0100

> On Monday 25 May 2009, Wolfgang Grandegger wrote:
>> > Right, that makes sense. However, most drivers use the field to store the
>> > physical address, not the iomap token. Maybe there should be a new field
>> > in struct sja1000_priv for the virtual address, but that would be a change
>> > to the base driver, not just to the OF portion.
>> 
>> Is that common practice? If yes, I will add a member to store the
>> virtual address to struct sja1000_priv.
> 
> I grepped through the network driver for usage of ->base_addr, and
> it's somewhat inconsistent. The majority of the users use it for
> a physical address, but there are also a few that use it for the
> __iomem token.
> 
> Casts between unsigned long and qualified (__iomem, __user, const, ...)
> pointers do not cause a warning, but can easily lead to bugs when
> another user casts to an unqualified pointer.

It's such a baroque thing, there is no reason to set it at all if you
ask me.  It's only use is to allow ISA and similar primitive bus
devices to have their I/O ports changed via ifconfig.