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Date:	Sun, 28 Dec 2014 11:05:04 +0200
From:	Oded Gabbay <oded.gabbay@....com>
To:	Christian König <deathsimple@...afone.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Alex Deucher <alexdeucher@...il.com>
CC:	Dana Elifaz <Dana.Elifaz@....com>, <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>,
	Alexander Deucher <Alexander.Deucher@....com>,
	LKP ML <lkp@...org>
Subject: Re: [LKP] [PATCH] drm/radeon: Try to init amdkfd only if 64 bit kernel



On 12/25/2014 02:31 PM, Christian König wrote:
> Am 22.12.2014 um 20:18 schrieb Oded Gabbay:
>>
>> On 12/22/2014 09:00 PM, Andi Kleen wrote:
>>> On Mon, Dec 22, 2014 at 10:49:40AM -0800, Andi Kleen wrote:
>>>> On Mon, Dec 22, 2014 at 11:58:43AM -0500, Alex Deucher wrote:
>>>>> On Mon, Dec 22, 2014 at 6:11 AM, Oded Gabbay <oded.gabbay@....com> wrote:
>>>>>> amdkfd driver can be compiled only in 64-bit kernel. Therefore, there is no
>>>>>> point in trying to initialize amdkfd in 32-bit kernel.
>>>>>>
>>>>>> In addition, in case of specific configuration of 32-bit kernel, no
>>>>>> modules and
>>>>>> random kernel base, the symbol_request function doesn't work as expected - It
>>>>>> doesn't return NULL if the symbol doesn't exists. That makes the kernel
>>>>>> panic.
>>>>>> Therefore, the as amdkfd doesn't compile in 32-bit kernel, the best way is
>>>>>> just
>>>>>> to return false immediately.
>>>>>>
>>>>>> Signed-off-by: Oded Gabbay <oded.gabbay@....com>
>>>>> Reviewed-by: Alex Deucher <alexander.deucher@....com>
>>>> Sorry but the patch is just bogus. X-bit only code is usually
>>>> a very bad sign for the code. This is not windows programing after all.
>> Hi Andi,
>>
>> Strange, I have never programmed for Windows in my life (except maybe in a
>> few courses during my degree) :)
>>>> Even if you wanted to do a 64bit only driver -- which
>>>> you probably don't -- the standard way would be to exclude
>>>> it in Kconfig.
>> So amdkfd actually *only* supports 64bit user processes, because AMD's HSA
>> stack on Linux supports *only* 64bit user processes. So, yes, I definitely
>> want to do a 64bit only driver.
>> If you look at kfd_open(), it fails the open of /dev/kfd if the process is
>> 32bit.
>> In addition, in Kconfig of amdkfd, it is written:
>> "depends on DRM_RADEON && AMD_IOMMU_V2 && X86_64"
>>
>> The problem here is that there is code in radeon, which is a driver that can
>> compile in 32bit, which tries to load amdkfd. I didn't see a point in trying
>> to load a driver which can't be compiled in 32bit.
>
> Well in this case couldn't we make the code in radeon depend on whether or not
> the KFD driver is compiled in or not instead of checking the system architecture?
>
> Regards,
> Christian.
>
If we are going down that path, we need something like:

bool radeon_kfd_init(void)
{
#if defined(CONFIG_HSA_AMD_MODULE)
	current code (symbol request and call to symbol)
#elif defined(CONFIG_HSA_AMD)
	direct call to kgd2kfd_init
#else
	return false;
#endif
}

Now, the original concept of the symbol_request call was to prevent writing 
something like the above pseudo-code, but because symbol_request is not 
currently working in all cases, I think that this is a good band-aid as any.

	Oded



>>
>>>> Please root-cause why symbol_request doesn't work on 32bit
>>>> and fix it properly.
>> I didn't say it doesn't always work.
>> The actual thing that doesn't work is the define symbol_get and only in a
>> specific case of 32bit kernel AND CONFIG_MODULES is unset AND
>> CONFIG_RANDOMIZE_BASE is set.
>> The define in that case is:
>> #define symbol_get(x) ({ extern typeof(x) x __attribute__((weak)); &(x); })
>>
>> Why it doesn't work (doesn't return NULL when symbol doesn't exists) ?
>> I don't know, probably because of some elf/makefile/c language magic. I'm
>> not that big of an expert on those issues, and I wanted to provide a fix for
>> this problem during the -rc stages. If someone can help me solving the root
>> cause, I would be more than happy.
>>
>>     Oded
>>>> +rusty.
>>> And also with correct email.
>>>
>>> -Andi
>>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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