linux-kernel - Re: [RFT v2] iommu/amd: use subsys

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Date:	Fri, 27 May 2016 02:12:43 +0200
From:	"Luis R. Rodriguez" <mcgrof@...nel.org>
To:	Wan Zongshun <vw@...mu.org>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Oded Gabbay <oded.gabbay@...il.com>,
	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

On Tue, Apr 19, 2016 at 10:02:52AM +0800, Wan Zongshun wrote:
> 
> 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, it turns out this is not exactly enough, given as 
Joerg notes:

--
AMD-KFD on the other hand needs to be loaded before the                                                                                          
radeon driver (but this it not enforced by symbols), because otherwise                                                                                        
the radeon driver will not initialize the AMD-KFD driver. 
---

We have a theoretical race still possible between the kfd module
and the drm driver. I'll reply to Joerg's e-mail with more feedback.

  Luis