[PATCH] Fix broken initialization when SCDC is supported but not implemented

[Giuseppe Ranieri]

This patch fix the missing scdc implementation on scdc enabled card behaviour 
init call and add debug message on error:

 - FIX: when the scdc implementation is missing the call of 
nvkm_uoutp_mthd_hdmi don't return anymore an error code but emit a OUTP_DBG log 
message and continue the initialization process

 - ADD: an NV_ERROR message where  error code is return by the nvif_outp_hdmi 
call in nv50_hdmi_enable method

Solve problem with (scdc enabled) card that don´t had scdc implementation in 
nouveau driver.

Signed-off-by: Giuseppe Ranieri <giuse...@ranieri.dev>
---

diff '--color=auto' -ur a/drivers/gpu/drm/nouveau/dispnv50/disp.c 
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c   2025-11-30 23:42:10.000000000 
+0100
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c   2026-01-17 01:27:34.150245394 
+0100
@@ -819,9 +819,11 @@
        ret = nvif_outp_hdmi(&nv_encoder->outp, nv_crtc->index, true, 
max_ac_packet, rekey,
                             mode->clock, hdmi->scdc.supported, 
hdmi->scdc.scrambling.supported,
                             hdmi->scdc.scrambling.low_rates);
-       if (ret)
+       if (ret < 0) {
+               NV_ERROR(drm, "Failure to set HDMI: %d\n", ret);
                return;
-
+       }
+       
        /* AVI InfoFrame. */
        args->version = 0;
        args->head = nv_crtc->index;
diff '--color=auto' -ur a/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c 
b/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c
--- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c  2025-11-30 
23:42:10.000000000 +0100
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/uoutp.c  2026-01-17 
01:20:03.670240977 +0100
@@ -253,8 +253,7 @@
 
        if (!ior->func->hdmi ||
            args->v0.max_ac_packet > 0x1f ||
-           args->v0.rekey > 0x7f ||
-           (args->v0.scdc && !ior->func->hdmi->scdc))
+           args->v0.rekey > 0x7f)
                return -EINVAL;
 
        if (!args->v0.enable) {
@@ -266,6 +265,11 @@
 
        ior->func->hdmi->ctrl(ior, args->v0.head, args->v0.enable,
                              args->v0.max_ac_packet, args->v0.rekey);
+       
+       if (args->v0.scdc && !ior->func->hdmi->scdc)
+               OUTP_DBG(outp, "SCDC enabled: %d, ior->func->hdmi->scdc not 
implemented (ior): %p", 
+                                     args->v0.scdc, ior);
+
        if (ior->func->hdmi->scdc)
                ior->func->hdmi->scdc(ior, args->v0.khz, args->v0.scdc, 
args->v0.scdc_scrambling,
                                      args->v0.scdc_low_rates);