LPT is pch, so might run into the fdi bandwidth constraint (especially
since it has only 2 lanes). But right now we just force pipe_bpp back
to 24, resulting in a nice loop (which we bail out with a loud
WARN_ON). Fix this.

Cc: Chris Wilson <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
References: https://bugs.freedesktop.org/show_bug.cgi?id=93477
Signed-off-by: Daniel Vetter <[email protected]>
---
 drivers/gpu/drm/i915/intel_crt.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index a2a31fd01d1d..3fbb6fc66451 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -261,8 +261,14 @@ static bool intel_crt_compute_config(struct intel_encoder 
*encoder,
                pipe_config->has_pch_encoder = true;
 
        /* LPT FDI RX only supports 8bpc. */
-       if (HAS_PCH_LPT(dev))
+       if (HAS_PCH_LPT(dev)) {
+               if (pipe_config->bw_constrained && pipe_config->pipe_bpp < 24) {
+                       DRM_DEBUG_KMS("LPT only supports 24bpp\n");
+                       return false;
+               }
+
                pipe_config->pipe_bpp = 24;
+       }
 
        /* FDI must always be 2.7 GHz */
        if (HAS_DDI(dev))
-- 
2.8.1

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