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

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Message-ID: <CADnq5_M32TX-TwTR-1hJ1=BMezpNDS7BLMmGXxi6ohNRjRDUjg@mail.gmail.com>
Date:	Fri, 20 Mar 2015 09:50:13 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Christian König <christian.koenig@....com>
Cc:	David Miller <davem@...emloft.net>,
	"Deucher, Alexander" <alexander.deucher@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] radeon: Do not directly dereference pointers to BIOS area.

On Fri, Mar 20, 2015 at 5:38 AM, Christian König
<christian.koenig@....com> wrote:
> 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.
>

Applied to my tree.  Thanks!

Alex
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