linux-kernel - Re: [PATCH 0/2] Change order of linkage in kernel makefiles for amdkfd

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Date:	Mon, 22 Dec 2014 12:56:14 +0100
From:	Christian König <christian.koenig@....com>
To:	Oded Gabbay <oded.gabbay@....com>, David Airlie <airlied@...ux.ie>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
CC:	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
	<iommu@...ts.linux-foundation.org>, Joerg Roedel <joro@...tes.org>,
	"Jerome Glisse" <j.glisse@...il.com>,
	John Bridgman <John.Bridgman@....com>,
	Alexander Deucher <Alexander.Deucher@....com>,
	Dana Elifaz <Dana.Elifaz@....com>,
	Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH 0/2] Change order of linkage in kernel makefiles for amdkfd

For this series: Reviewed-by: Christian König <christian.koenig@....com>

Am 22.12.2014 um 12:07 schrieb Oded Gabbay:
> This small patch-set, was created to solve the bug described at
> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
> trying use amdkfd driver on Kaveri). It replaces the previous patch-set called
> [PATCH 0/3] Use workqueue for device init in amdkfd
> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html)
>
> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
> inside the kernel (not as modules). In that case, the correct loading
> order, as determined by the exported symbol used by each driver, is
> not enforced anymore and the kernel loads them based on who was linked
> first. That makes radeon load first, amdkfd second and amd_iommu_v2
> third.
>
> Because the initialization of a device in amdkfd is initiated by radeon,
> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
> initialized, then in the case mentioned above, this initalization fails
> and there is a kernel panic as some pointers are not initialized but
> used nontheless.
>
> To solve this bug, this patch-set moves iommu/ before gpu/ in drivers/Makefile
> and also moves amdkfd/ before radeon/ in drivers/gpu/drm/Makefile.
>
> The rationale is that in general, AMD GPU devices are dependent on AMD IOMMU
> controller functionality to allow the GPU to access a process's virtual memory
> address space, without the need for pinning the memory. That's why it makes
> sense to initialize the iommu/ subsystem ahead of the gpu/ subsystem.
>
> 	Oded
>
> Oded Gabbay (2):
>    drivers: Move iommu/ before gpu/ in Makefile
>    drm: Put amdkfd before radeon in drm Makefile
>
>   drivers/Makefile         | 6 ++++--
>   drivers/gpu/drm/Makefile | 2 +-
>   2 files changed, 5 insertions(+), 3 deletions(-)
>

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