[PATCH] drm/amdgpu: Don't default to DC support for Kaveri and older

[Harry Wentland <harry.wentland-5C7GfCeVMHo@public.gmane.org>]

We've had a number of users report failures to detect and light up
display with DC with LVDS and VGA. These connector types are not
currently supported with DC. I'd like to add support but unfortunately
don't have a system with LVDS or VGA available.

In order not to cause regressions we should probably fallback to the
non-DC driver for ASICs that support VGA and LVDS.

These ASICs are:
 * Hawaii
 * Bonaire
 * Kabini
 * Kaveri

ASIC support can always be force enabled with amdgpu.dc=1

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 887f7c9e84e0..66d8b96a04ac 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -2144,6 +2144,14 @@ bool amdgpu_device_asic_has_dc_support(enum amd_asic_type asic_type)
 	case CHIP_HAWAII:
 	case CHIP_KAVERI:
 	case CHIP_KABINI:
+		/*
+		 * We have systems in the wild with these ASICs that require
+		 * LVDS and VGA support which is not supported with DC.
+		 *
+		 * Fallback to the non-DC driver here by default so as not to
+		 * cause regressions.
+		 */
+		return amdgpu_dc > 0;
 	case CHIP_MULLINS:
 	case CHIP_CARRIZO:
 	case CHIP_STONEY:
-- 
2.17.0

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