drm/i915: WARN in case we're enabling the pipe and it's enabled

... and QUIRK_PIPEA_FORCE is not present.

I initially thought that case was impossible and just added a WARN on
it, but then I was told this case is possible due to
QUIRK_PIPEA_FORCE. So let's add a WARN that serves two purposes:
  - tell us in case we have done something wrong;
  - document the only case where we expect this.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b040bd4..43b4281 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1793,8 +1793,11 @@ static void intel_enable_pipe(struct intel_crtc *crtc)
 
        reg = PIPECONF(cpu_transcoder);
        val = I915_READ(reg);
-       if (val & PIPECONF_ENABLE)
+       if (val & PIPECONF_ENABLE) {
+               WARN_ON(!(pipe == PIPE_A &&
+                         dev_priv->quirks & QUIRK_PIPEA_FORCE));
                return;
+       }
 
        I915_WRITE(reg, val | PIPECONF_ENABLE);
        POSTING_READ(reg);