drm/i915/display: Set TRANS_DDI_MODE_SELECT to default value when clearing DDI select

TGL is suffering of timeouts and fifo underruns when disabling
transcoder in MST mode, this is fixed by set TRANS_DDI_MODE_SELECT to
0(HDMI mode) when clearing DDI select.

Although BSpec disable sequence don't require this step, it is a
harmless change and it is also done by Windows driver.
Anyhow HW team was notified about that but it can take some time to
documentation to be updated.

A case that always lead to those issues is:
- do a modeset enabling pipe A and pipe B in the same MST stream
leaving A as master
- disable pipe A, promote B as master doing a full modeset in A
- enable pipe A, changing the master transcoder back to A(doing a
full modeset in B)
- Pow: underruns and timeouts

The transcoders involved will only work again when complete disabled
and their power wells turned off causing a reset in their registers.

v2: Setting TRANS_DDI_MODE_SELECT to default when clearing DDI select
not anymore when disabling TRANS_DDI, both work but this one looks
more safe. (Ville comment)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200203225549.152301-1-jose.souza@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
index 1ab638e..4c5f32e 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_ddi.c
+++ b/drivers/gpu/drm/i915/display/intel_ddi.c
@@ -1988,10 +1988,12 @@ void intel_ddi_disable_transcoder_func(const struct intel_crtc_state *crtc_state
        val &= ~TRANS_DDI_FUNC_ENABLE;
 
        if (INTEL_GEN(dev_priv) >= 12) {
-               if (!intel_dp_mst_is_master_trans(crtc_state))
-                       val &= ~TGL_TRANS_DDI_PORT_MASK;
+               if (!intel_dp_mst_is_master_trans(crtc_state)) {
+                       val &= ~(TGL_TRANS_DDI_PORT_MASK |
+                                TRANS_DDI_MODE_SELECT_MASK);
+               }
        } else {
-               val &= ~TRANS_DDI_PORT_MASK;
+               val &= ~(TRANS_DDI_PORT_MASK | TRANS_DDI_MODE_SELECT_MASK);
        }
        intel_de_write(dev_priv, TRANS_DDI_FUNC_CTL(cpu_transcoder), val);
 
@@ -3728,7 +3730,8 @@ static void intel_ddi_post_disable_dp(struct intel_encoder *encoder,
 
                        val = intel_de_read(dev_priv,
                                            TRANS_DDI_FUNC_CTL(cpu_transcoder));
-                       val &= ~TGL_TRANS_DDI_PORT_MASK;
+                       val &= ~(TGL_TRANS_DDI_PORT_MASK |
+                                TRANS_DDI_MODE_SELECT_MASK);
                        intel_de_write(dev_priv,
                                       TRANS_DDI_FUNC_CTL(cpu_transcoder),
                                       val);