linux-kernel - Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)

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Message-ID: <1360066756.4529.6.camel@pasglop>
Date:	Tue, 05 Feb 2013 23:19:16 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Michal Simek <monstr@...str.eu>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	linux-kernel@...r.kernel.org, grant.likely@...retlab.ca,
	alan@...rguk.ukuu.org.uk, geert@...ux-m68k.org,
	dahinds@...rs.sourceforge.net
Subject: Re: [PATCH] drivers/block/xsysace - replace
 in(out)_8/in(out)_be16/in(out)_le16 with generic iowrite(read)8/16(be)

On Tue, 2013-02-05 at 11:54 +0100, Michal Simek wrote:
> 
> xilinx ppc is big endian
> xilinx arm is little endian
> xilinx microblaze is little endian and big endian

You are talking about the core, why should the xsysace block driver be
synthesized with the same endianness as the core ? That's not terribly
useful, especially since reverse load/stores on ppc are essentially
free...

> It is just sharing the same IP across all platforms. Which is better
> than create new devices and new device drivers for it. It means that
> all of them are register compatible but require access with native
> platform endianness as I listed above.

Every attempt at doing "native platform endianness" has always been a
misguided attempt turning into a trainwreck (see OHCI USB).

Just pick one endian for the device and stick to it.

> It is not a problem to create runtime wrapper and even detect endian
> directly in the driver
> but the point if this is the proper design.
> Also ioread32 and ioread32be shouldn't be used on ARM because there
> are missing memory barriers.

Then fix them, they shouldn't be, it's a bug, it will break many other
drivers. They should be fully equivalent to readl.

Ben.


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