Running an rv790 I haven't used s-vid TV for a while so am a month late noticing it had regressed on d-r-t.

Booting old kernels and then using git reset I found the guilty commit to be -

commit 5b1714d386a2f0c0d270e3abe1ac39ad1b0ba010
Author: Alex Deucher <alexdeucher@gmail.com>
Date:   Tue Aug 3 19:59:20 2010 -0400

    drm/radeon/kms: enable underscan option for digital connectors

As it won't revert from d-r-t head I took a closer look and thought this bit to be suspicious -

@@ -1176,10 +1170,8 @@ int atombios_crtc_mode_set(struct drm_crtc *crtc,
        atombios_crtc_set_pll(crtc, adjusted_mode);
        atombios_enable_ss(crtc);
 
-       if (ASIC_IS_DCE4(rdev))
+       if (ASIC_IS_AVIVO(rdev))
                atombios_set_crtc_dtd_timing(crtc, adjusted_mode);
-       else if (ASIC_IS_AVIVO(rdev))
-               atombios_crtc_set_timing(crtc, adjusted_mode);
        else {
                atombios_crtc_set_timing(crtc, adjusted_mode);
                if (radeon_crtc->crtc_id == 0)


So I edited by hand to swap back the atombios_crtc_set_timing for AVIVO and the other one for the rest -

diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c
index 577239a..40ca121 100644
--- a/drivers/gpu/drm/radeon/atombios_crtc.c
+++ b/drivers/gpu/drm/radeon/atombios_crtc.c
@@ -1208,9 +1208,9 @@ int atombios_crtc_mode_set(struct drm_crtc *crtc,
        atombios_enable_ss(crtc);
 
        if (ASIC_IS_AVIVO(rdev))
-               atombios_set_crtc_dtd_timing(crtc, adjusted_mode);
-       else {
                atombios_crtc_set_timing(crtc, adjusted_mode);
+       else {
+               atombios_set_crtc_dtd_timing(crtc, adjusted_mode);
                if (radeon_crtc->crtc_id == 0)
                        atombios_set_crtc_dtd_timing(crtc, adjusted_mode);
                radeon_legacy_atom_fixup(crtc);


and now have working TV again. I also tested turning on underscan on my DVI monitor and it still works.