linux-kernel - Re: [PATCH] fbmem: Fix fb_read, fb

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Message-Id: <20100921161950.b7f45273.akpm@linux-foundation.org>
Date:	Tue, 21 Sep 2010 16:19:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	James Hogan <james@...anarts.com>
Cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Dave Airlie <airlied@...hat.com>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	James Simmons <jsimmons@...radead.org>
Subject: Re: [PATCH] fbmem: Fix fb_read, fb_write unaligned accesses.

On Sat, 18 Sep 2010 01:23:47 +0100
James Hogan <james@...anarts.com> wrote:

> Apologies for corrupted patch. I'll try again.
> Comments? I'd also appreciate if somebody familiar with sbus on sparc
> could check this patch is sane since I know virtually nothing about sbus
> and am not in a position to compile for sparc, let alone test on it:
> 
> fb_{read,write} access the framebuffer using lots of fb_{read,write}l's
> but don't check that the file position is aligned which can cause
> problems on some architectures which do not support unaligned accesses.

What are these "problems"?

I'd have thought they would be fairly fatal, in which case this is a
high-priority patch.  But I'd also have thought that the problems would
have been noted before now.

So I assume that you're doing something which nobody has done before.

Confused.  Help?

> Since the operations are essentially memcpy_{from,to}io, new
> fb_memcpy_{from,to}fb macros have been defined and these are used
> instead.
> 
> For Sparc, fb_{read,write} macros use sbus_{read,write}, so this defines
> new sbus_memcpy_{from,to}io functions the same as memcpy_{from,to}io but
> using sbus_{read,write}b instead of {read,write}b.
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