linux-kernel - RE: [PATCH] radeon: Do not directly dereference pointers to BIOS area.

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Message-ID: <A3397C8B8B789E45844E7EC5DEAD89D06361CFD2@satlexdag05.amd.com>
Date:	Fri, 20 Mar 2015 17:39:02 +0000
From:	"Deucher, Alexander" <Alexander.Deucher@....com>
To:	David Miller <davem@...emloft.net>,
	"Koenig, Christian" <Christian.Koenig@....com>
CC:	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] radeon: Do not directly dereference pointers to BIOS
 area.

> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Friday, March 20, 2015 1:24 PM
> To: Koenig, Christian
> Cc: Deucher, Alexander; dri-devel@...ts.freedesktop.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH] radeon: Do not directly dereference pointers to BIOS
> area.
> 
> From: Christian König <christian.koenig@....com>
> Date: Fri, 20 Mar 2015 10:38:32 +0100
> 
> > On 19.03.2015 17:29, David Miller wrote:
> >> From: Christian König <christian.koenig@....com>
> >> Date: Thu, 19 Mar 2015 09:50:58 +0100
> >>
> >>> In general I would say yes, but for this particular hardware it's a
> >>> bit questionable to do so.
> >>>
> >>> For radeon hardware to work correctly the CPU access to the PCIE BARs
> >>> should work even without using the specialized IO macros/functions,
> >>> otherwise mapping VRAM CPU accessible isn't really possible.
> >>>
> >>> What's the background of the change? Some problems on a certain CPU
> >>> platform? or just general cleanups?
> >> It's an _iomem_ pointer, it's not a virtual address.
> >>
> >> Therefore it is illegal to dereference the pointer.
> >>
> >> The value is opaque and has values that only make sense when used
> >> with the readb() et al. interfaces.
> >>
> >> This code is relying upon the fact that on x86 it happens to be
> >> a virtual address, but this won't work on many other architectures.
> >
> > In this case I'm perfectly fine with it and the patch is Reviewed-by:
> > Christian König <christian.koenig@....com>
> >
> > Just wanted to make sure that you're not trying to get Radeon working
> > on a platform which will never really support the necessary hardware
> > features.
> 
> I would like this to get merged via the Radeon DRM maintainer, thanks.

Already added to my tree.  Thanks!

Alex
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