drm/nv17-nv4x: Fix analog load detection false positive on rare occasions.

On some boards the residual current DAC outputs can draw when they're
disconnected can be high enough to give a false load detection
positive (I've only seen it in the S-video luma output of some cards,
but just to be sure). The output line capacitance is limited and
sampling twice should fix it reliably.

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nv04_dac.c b/drivers/gpu/drm/nouveau/nv04_dac.c
index ea3627041ecf..509c05015d50 100644
--- a/drivers/gpu/drm/nouveau/nv04_dac.c
+++ b/drivers/gpu/drm/nouveau/nv04_dac.c
@@ -291,6 +291,8 @@ uint32_t nv17_dac_sample_load(struct drm_encoder *encoder)
         msleep(5);
 
         sample = NVReadRAMDAC(dev, 0, NV_PRAMDAC_TEST_CONTROL + regoffset);
+        /* do it again just in case it's a residual current */
+        sample &= NVReadRAMDAC(dev, 0, NV_PRAMDAC_TEST_CONTROL + regoffset);
 
         temp = NVReadRAMDAC(dev, head, NV_PRAMDAC_TEST_CONTROL);
         NVWriteRAMDAC(dev, head, NV_PRAMDAC_TEST_CONTROL,