Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Dirk Gouders <dirk@gouders.net>
To:     Alex Deucher <alexander.deucher@amd.com>
Cc:     Christian =?utf-8?Q?K=C3=B6nig?= <christian.koenig@amd.com>,
        linux-kernel@vger.kernel.org
Cc:     amd-gfx@lists.freedesktop.org,
        Hawking Zhang <Hawking.Zhang@amd.com>,
        Evan Quan <evan.quan@amd.com>
Subject: BUG: amdgpu: NULL pointer dereference introduced in 5.9-rc1
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux)
Date:   Wed, 30 Sep 2020 22:13:23 +0200
Message-ID: <ghmu1758gs.fsf@gouders.net>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Commit c1cf79ca5ced46 (drm/amdgpu: use IP discovery table for renoir)
introduced a NULL pointer dereference when booting with
amdgpu.discovery=0.

For amdgpu.discovery=0 that commit effectively removed the call of
vega10_reg_base_init(adev), so I tested the correctness of the bisect
session by restoring that function call for amdgpu_discovery == 0 and with
that change, the NULL pointer dereference does not occur:

diff --git a/drivers/gpu/drm/amd/amdgpu/soc15.c b/drivers/gpu/drm/amd/amdgpu/soc15.c
index 84d811b6e48b..2e93c5e1e7e6 100644
--- a/drivers/gpu/drm/amd/amdgpu/soc15.c
+++ b/drivers/gpu/drm/amd/amdgpu/soc15.c
@@ -699,7 +699,8 @@ static void soc15_reg_base_init(struct amdgpu_device *adev)
                                         "fallback to legacy init method\n");
                                vega10_reg_base_init(adev);
                        }
-               }
+               } else
+                       vega10_reg_base_init(adev);
                break;
        case CHIP_VEGA20:
                vega20_reg_base_init(adev);

Dirk