[REGRESSION][PATCH] drm/amd/display: Fix uninitialized variable which breaks full LTO

[Calvin Owens <calvin@wbinvd.org>]

Commit e1b385726f7f ("drm/amd/display: Add additional checks for PSP
footer size") introduced a use of an uninitialized stack variable
in dm_dmub_sw_init() (region_params.bss_data_size).

Interestingly, this seems to cause no issue on normal kernels. But when
full LTO is enabled, it causes the compiler to "optimize" out huge
swaths of amdgpu initialization code, and the driver is unusable:

    amdgpu 0000:03:00.0: [drm] Loading DMUB firmware via PSP: version=0x07002F00
    amdgpu 0000:03:00.0: sw_init of IP block <dm> failed 5
    amdgpu 0000:03:00.0: amdgpu_device_ip_init failed
    amdgpu 0000:03:00.0: Fatal error during GPU init

It surprises me that neither gcc nor clang emit a warning about this: I
only found it by bisecting the LTO breakage.

Fix by using the old value for region_params.bss_data_size in place of
the uninitialized reference, which makes amdgpu work with LTO again.

Fixes: e1b385726f7f ("drm/amd/display: Add additional checks for PSP footer size")
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index b3d6f2cd8ab6..e69e61163ae9 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -2554,7 +2554,7 @@ static int dm_dmub_sw_init(struct amdgpu_device *adev)
 	fw_meta_info_params.fw_inst_const = adev->dm.dmub_fw->data +
 					    le32_to_cpu(hdr->header.ucode_array_offset_bytes) +
 					    PSP_HEADER_BYTES_256;
-	fw_meta_info_params.fw_bss_data = region_params.bss_data_size ? adev->dm.dmub_fw->data +
+	fw_meta_info_params.fw_bss_data = le32_to_cpu(hdr->bss_data_bytes) ? adev->dm.dmub_fw->data +
 					  le32_to_cpu(hdr->header.ucode_array_offset_bytes) +
 					  le32_to_cpu(hdr->inst_const_bytes) : NULL;
 	fw_meta_info_params.custom_psp_footer_size = 0;
-- 
2.47.3