netdev - Re: [PATCH 2/14] nes: device structures and defines

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Message-ID: <46B9ECFD.1070700@garzik.org>
Date:	Wed, 08 Aug 2007 12:19:09 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	ggrundstrom@...effect.com, rdreier@...co.com,
	ewg@...ts.openfabrics.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/14] nes: device structures and defines

Andi Kleen wrote:
> Jeff Garzik <jeff@...zik.org> writes:
>>> +			val, reg_index, addr, addr+4); */
>>> +	writel(cpu_to_le32(reg_index), addr);
>>> +	writel(cpu_to_le32(val),(u8 *)addr + 4);
>> wrong -- endian conversion macros not needed with writel()
> 
> Are you sure?

Yes.

read[bwl] and write[bwl] are always defined in terms of the 
little-endian PCI bus.  This has been true since my first days in the 
kernel ages (decade+) ago, when we had a long discussion about it with 
regards to framebuffer drivers.

If you want to skip barriers and endian conversions, __raw_write[bwl]() 
exists.

The rare exceptions are a few embedded arches that implemented writel() 
for a non-PCI bus.  Those cases need to be renamed to mybus_writel(), 
but at least they do not interfere with mainstream drivers and APIs.

> I don't think that's true. e.g. powerpc writel 
> doesn't convert endian

Incorrect -- read the code.  PPC most certainly does convert endian.

Ten years ago Linus said something along the lines of "writel() means 
PCI means little endian.  period."  ;-)

	Jeff

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