[GM965] Why does this patch fix my Intel TVOut issue?

[Robert Lowery]

Hi Folks,

I've never been able to obtain reliable (ie non blank) TV output on my
AOpen MP965-DR (GM965 based) HTPC.  Spending some time investigating, I
have found the patch below works around the problem.

diff --git a/src/i830_tv.c b/src/i830_tv.c
index 6adb9f2..f442a4f 100644
--- a/src/i830_tv.c
+++ b/src/i830_tv.c
@@ -1297,7 +1297,7 @@ i830_tv_detect_type (xf86CrtcPtr    crtc,
                DAC_A_0_7_V |
                DAC_B_0_7_V |
                DAC_C_0_7_V);
-       OUTREG(TV_CTL, tv_ctl);
+       //OUTREG(TV_CTL, tv_ctl);
        OUTREG(TV_DAC, tv_dac);
        i830WaitForVblank(pScrn);
        tv_dac = INREG(TV_DAC);
@@ -1316,6 +1316,7 @@ i830_tv_detect_type (xf86CrtcPtr    crtc,
                       "Detected Composite TV connection\n");
        }
        type = TV_TYPE_COMPOSITE;
+       type = TV_TYPE_COMPONENT;
     } else if ((tv_dac & (TVDAC_A_SENSE|TVDAC_B_SENSE)) == TVDAC_A_SENSE) {
        if (pI830->debug_modes) {
            xf86DrvMsg(pScrn->scrnIndex, X_INFO,

Basically I have turned off the code that disables the encoder and puts it
into detection mode (stopping TV_CTL from being changed from TV_ENC_ENABLE
| TV_OVERSAMPLE_8X to TV_TEST_MODE_MONITOR_DETECT | TV_OVERSAMPLE_8X). 
Note the second part of the diff that forces TV_TYPE_COMPONENT is really
only required due to the detection mode being disabled, I believe the crux
of the issue is in restoration of TV_CTL.

I've also tried swapping the TV_DAC and TV_CTL restoration order and
setting TV_DAC to 0 before restoring TV_CTL, but neither resolve the
problem.  Is there something special that needs to be done when restoring
TV_CTL?

Suggestions welcome.

Thanks

-Rob