Date:	Tue, 19 Apr 2016 10:02:52 +0800
From:	Wan Zongshun <vw@...mu.org>
To:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Oded Gabbay <oded.gabbay@...il.com>
Cc:	Christian König <christian.koenig@....com>,
	iommu@...ts.linux-foundation.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Wan Zongshun <vincent.wan@....com>
Subject: Re: [RFT v2] iommu/amd: use subsys_initcall() on amdv2 iommu



-------- Original Message --------
> On Mon, Apr 18, 2016 at 10:02:24AM +0300, Oded Gabbay wrote:
>> On Mon, Apr 18, 2016 at 9:55 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
>>>
>>> On Apr 18, 2016 7:48 AM, "Oded Gabbay" <oded.gabbay@...il.com> wrote:
>>>>
>>>> On Wed, Apr 13, 2016 at 1:07 AM, Luis R. Rodriguez <mcgrof@...nel.org>
>>>> wrote:
>>>>> On Mon, Apr 11, 2016 at 03:52:43PM +0200, Christian König wrote:
>>>>>> Am 11.04.2016 um 15:39 schrieb Oded Gabbay:
>>>>>>> On Mon, Apr 11, 2016 at 4:28 PM, Christian König
>>>>>>> <christian.koenig@....com> wrote:
>>>>>>>> Am 09.04.2016 um 02:25 schrieb Luis R. Rodriguez:
>>>>>>>>> On Tue, Mar 29, 2016 at 10:41 AM, Luis R. Rodriguez
>>>>>>>>> <mcgrof@...nel.org> wrote:
>>>>>>>>>> We need to ensure amd iommu v2 initializes before
>>>>>>>>>> driver uses such as drivers/gpu/drm/amd/amdkfd/kfd_module.c,
>>>>>>>>>> to do this make its init routine a subsys_initcall() which
>>>>>>>>>> ensures its load init is called first than modules when
>>>>>>>>>> built-in.
>>>>>>>>>>
>>>>>>>>>> This reverts the old work around implemented through commit
>>>>>>>>>> 1bacc894c227fad8a7 ("drivers: Move iommu/ before gpu/ in
>>>>>>>>>> Makefile"),
>>>>>>>>>> instead of making the dependency implicit by linker order this
>>>>>>>>>> makes the ordering requirement explicit through proper kernel
>>>>>>>>>> APIs.
>>>>>>>>>>
>>>>>>>>>> Cc: Oded Gabbay <oded.gabbay@....com>
>>>>>>>>>> Cc: Christian König <christian.koenig@....com>
>>>>>>>>>> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
>>>>>>>>
>>>>>>>> Sorry for not responding earlier. Just coming back to all the stuff
>>>>>>>> on my TODO list.
>>>>>>>>
>>>>>>>> Patch is Acked-by: Christian König <christian.koenig@....com>
>>>>>>>
>>>>>>> Christian,
>>>>>>> Just wanted to be sure if you tested this patch-set or not.
>>>>>>
>>>>>> I did NOT tested it. If AMD IOMMU requires something which will now
>>>>>> initialize after the IOMMU module we will obviously run into trouble
>>>>>> again.
>>>>>>
>>>>>> I assumed that the creator of the patch did some testing.
>>>>>
>>>>> Nope, hence [RTF] Request For Testing.
>>>>>
>>>>>>> I don't think it should be merged without testing. If you already
>>>>>>> tested it than fine. If not, I think I can do it in the next week or
>>>>>>> so (just came back from PTO).
>>>>>>
>>>>>> Yeah, agree totally.
>>>>>
>>>>> Agreed, please let me know if someone is able to test and confirm
>>>>> this works. It should work.
>>>>>
>>>>>    Luis
>>>>
>>>> Hi,
>>>> So I finally got to test this patch and it's not working.
>>>> The reason is that AMD IOMMUv2 gets initialized *before* AMD IOMMUv1
>>>> driver !
>>>
>>> Thanks can you try using late_initcall() instead then?
>>>
>>>    Luis
>>
>> That will make it initialize *after* drm subsystem, which will cause
>> another bug.
>
> Hold up, I thought that we needed AMD IOMMUv2 to get initialized
> before AMD IOMMUv1 ? That's what the patch did. Can someone clarify
> the requirements then?

We must keep AMD IOMMUv2 to get initialized after AMD IOMMUv1， So your 
patch make the sequence reverse.

>
> I'll provide some review of the current state of affairs first, without the
> patch. AMD IOMMUv1 uses x86_init.iommu.iommu_init and that has its own init
> semantics. Specifically that gets called via pci_iommu_init() which is pegged
> on the init order via rootfs_initcall(pci_iommu_init);
>
> Then AMD IOMMUv2 uses module_init() and that when is built-in falls on to
> __initcall() which is device_initcall().

Exactly, it is amd iommu v1 v2 call sequence.
>
> The order is:
>
> #define pure_initcall(fn)               __define_initcall(fn, 0)
>
> #define core_initcall(fn)               __define_initcall(fn, 1)
> #define core_initcall_sync(fn)          __define_initcall(fn, 1s)
> #define postcore_initcall(fn)           __define_initcall(fn, 2)
> #define postcore_initcall_sync(fn)      __define_initcall(fn, 2s)
> #define arch_initcall(fn)               __define_initcall(fn, 3)
> #define arch_initcall_sync(fn)          __define_initcall(fn, 3s)
> #define subsys_initcall(fn)             __define_initcall(fn, 4)
> #define subsys_initcall_sync(fn)        __define_initcall(fn, 4s)
> #define fs_initcall(fn)                 __define_initcall(fn, 5)
> #define fs_initcall_sync(fn)            __define_initcall(fn, 5s)
> #define rootfs_initcall(fn)             __define_initcall(fn, rootfs)
> #define device_initcall(fn)             __define_initcall(fn, 6)
> #define device_initcall_sync(fn)        __define_initcall(fn, 6s)
> #define late_initcall(fn)               __define_initcall(fn, 7)
> #define late_initcall_sync(fn)          __define_initcall(fn, 7s)
>
> So technically rootfs_initcall() (v1 amd) should be being called
> first already, and after that AMD IOMMUv2 gets called next.
>
> You said that with my patch you saw AMD IOMMUv2 kick off first,
> that was intentional as I thought that's what you needed. Can
> someone please describe the requirements?
>
> Also what does drm use that you say has a conflict already? What
> drm code are we talking about exactly ?

You have to take carefully to arrange the calling sequence for iommuv1, 
iommuv2, kfd module, and drm like the following sequence : v1 ->v2->kfd, 
drm.

iommuv1 -- rootfs_initcall(fn)
IOMMUV2 -- device_initcall(fn)
kfd module -- late_initcall(fn)
drm -- late_initcall(fn)

Thanks!
Wan Zongshun.

>
>    Luis
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