On Thu, 02 Jan 2025, Imre Deak <imre.deak@xxxxxxxxx> wrote:
> On Thu, Dec 19, 2024 at 11:34:02PM +0200, Jani Nikula wrote:
>> We'll want to distinguish 128b/132b SST and MST modes at state
>> readout. There's a catch, though. From the hardware perspective,
>> 128b/132b SST and MST programming are pretty much the same. And we can't
>> really ask the sink at this point.
>>
>> If we have more than one transcoder in 128b/132b mode associated with
>> the port, we can safely assume it's MST. But for MST with only a single
>> stream enabled, we are pretty much out of luck. Let's fall back to
>> looking at the software state, i.e. intel_dp->is_mst. It should be fine
>> for the state checker, but for hardware takeover at probe, we'll have to
>> trust the GOP has only enabled SST.
>>
>> TODO: Not sure how this *or* our current code handles 128b/132b enabled
>> by GOP.
>>
>> Cc: Imre Deak <imre.deak@xxxxxxxxx>
>> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
>> ---
>> drivers/gpu/drm/i915/display/intel_ddi.c | 29 +++++++++++++++++++-----
>> 1 file changed, 23 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
>> index 7b739b9c5a06..04118f2eea94 100644
>> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
>> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
>> @@ -786,7 +786,7 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
>> intel_wakeref_t wakeref;
>> enum pipe p;
>> u32 tmp;
>> - u8 mst_pipe_mask;
>> + u8 mst_pipe_mask = 0, dp128b132b_pipe_mask = 0;
>>
>> *pipe_mask = 0;
>> *is_dp_mst = false;
>> @@ -823,7 +823,6 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
>> goto out;
>> }
>>
>> - mst_pipe_mask = 0;
>> for_each_pipe(dev_priv, p) {
>> enum transcoder cpu_transcoder = (enum transcoder)p;
>> u32 port_mask, ddi_select, ddi_mode;
>> @@ -852,9 +851,10 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
>>
>> ddi_mode = tmp & TRANS_DDI_MODE_SELECT_MASK;
>>
>> - if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST ||
>> - (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display)))
>> + if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST)
>> mst_pipe_mask |= BIT(p);
>> + else if (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display))
>> + dp128b132b_pipe_mask |= BIT(p);
>>
>> *pipe_mask |= BIT(p);
>> }
>> @@ -864,6 +864,23 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
>> "No pipe for [ENCODER:%d:%s] found\n",
>> encoder->base.base.id, encoder->base.name);
>>
>> + if (!mst_pipe_mask && dp128b132b_pipe_mask) {
>> + struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>> +
>
> 8b10b and 128b132b can't be mixed on one link, so the above could make
> this clear (and more robust) by
>
> if (dp128b132b_pipe_mask) {
> if (WARN(mst_pipe_mask))
> mst_pipe_mask = 0;
They can't be mixed, but doesn't mean the registers can't contain that
stuff!
The point is any goof-ups like that get caught in one place below...
> In any case the patch is correct, so either way:
>
> Reviewed-by: Imre Deak <imre.deak@xxxxxxxxx>
>
>> + /*
>> + * If we don't have 8b/10b MST, but have more than one
>> + * transcoder in 128b/132b mode, we know it must be 128b/132b
>> + * MST.
>> + *
>> + * Otherwise, we fall back to checking the current MST
>> + * state. It's not accurate for hardware takeover at probe, but
>> + * we don't expect MST to have been enabled at that point, and
>> + * can assume it's SST.
>> + */
>> + if (hweight8(dp128b132b_pipe_mask) > 1 || intel_dp->is_mst)
>> + mst_pipe_mask = dp128b132b_pipe_mask;
>> + }
>> +
>> if (!mst_pipe_mask && hweight8(*pipe_mask) > 1) {
>> drm_dbg_kms(&dev_priv->drm,
>> "Multiple pipes for [ENCODER:%d:%s] (pipe_mask %02x)\n",
>> @@ -874,9 +891,9 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
>>
>> if (mst_pipe_mask && mst_pipe_mask != *pipe_mask)
...here. If both mst_pipe_mask != 0 and dp128b132b_pipe_mask != 0, then
mst_pipe_mask != *pipe_mask.
BR,
Jani.
>> drm_dbg_kms(&dev_priv->drm,
>> - "Conflicting MST and non-MST state for [ENCODER:%d:%s] (pipe_mask %02x mst_pipe_mask %02x)\n",
>> + "Conflicting MST and non-MST state for [ENCODER:%d:%s] (pipe masks: all %02x, MST %02x, 128b/132b %02x)\n",
>> encoder->base.base.id, encoder->base.name,
>> - *pipe_mask, mst_pipe_mask);
>> + *pipe_mask, mst_pipe_mask, dp128b132b_pipe_mask);
>> else
>> *is_dp_mst = mst_pipe_mask;
>>
>> --
>> 2.39.5
>>
--
Jani Nikula, Intel
