From: Arnd Bergmann <arnd@arndb.de>
To: Rob Clark <rob.clark@linaro.org>
Subject: Re: [PATCH] ARM: add get_user() support for 8 byte types
Date: Thu, 15 Nov 2012 14:39:41 +0000
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Cc: "Russell King - ARM Linux" <linux@arm.linux.org.uk>,
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        linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
        dri-devel@lists.freedesktop.org
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On Thursday 15 November 2012, Rob Clark wrote:
> > I still haven't heard a conclusive argument why we need to use get_user()
> > rather than copy_from_user() in the DRM code. Is this about a fast path
> > where you want to shave off a few cycles for each call, or does this
> > simplify the code structure, or something else?
> 
> well, it is mostly because it seemed like a good idea to first try to
> solve the root issue, rather than having to fix things up in each
> driver when someone from x86-world introduces a 64b get_user()..

As pointed out by hpa earlier, x86-32 doesn't have a 64b get_user
either. I don't think we have a lot of drivers that are used only
on 64-bit x86 and on 32-bit ARM but not on 32-bit x86.

> There are some other arch's that don't have 64b get_user(), but I
> don't think any that have any DRM drivers.  If 64b get_user() is
> really not intended to be supported by all archs, it is better to
> remove it from x86 and the other arch's that do currently support it,
> rather than making it possible to write drivers that are broken on
> some archs.

The majority of architectures we support have PCI and should be able
to build the regular (radeon, nouveau, MGA, VIA, ...) DRM drivers
AFAICT.

	Arnd
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