RE: [PATCHv2] drm/i915/dp: Guarantee a minimum HBlank time

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 22 Oct 2024, "Murthy, Arun R" <arun.r.murthy@intel.com> wrote:
>> -----Original Message-----
>> From: Jani Nikula <jani.nikula@linux.intel.com>
>> Sent: Tuesday, October 22, 2024 1:04 PM
>> To: Murthy, Arun R <arun.r.murthy@intel.com>; intel-xe@lists.freedesktop.org;
>> intel-gfx@lists.freedesktop.org
>> Cc: Murthy, Arun R <arun.r.murthy@intel.com>
>> Subject: Re: [PATCHv2] drm/i915/dp: Guarantee a minimum HBlank time
>> 
>> On Tue, 01 Oct 2024, Arun R Murthy <arun.r.murthy@intel.com> wrote:
>> > Mandate a minimum Hblank symbol cycle count between BS and BE in
>> > 8b/10b MST and 12b/132b mode.
>> 
>> Should be 128b.
>> 
> Done
>
>> What are BS and BE? I'm not asking specifically for *me*. The commit message
>> needs to have more clarity.
>> 
> ok
>> > Spec: DP2.1a
>> >
>> > v2: Affine calculation/updation of min HBlank to dp_mst (Jani)
>> >
>> > Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
>> > ---
>> >  .../drm/i915/display/intel_display_types.h    |  2 ++
>> >  drivers/gpu/drm/i915/display/intel_dp_mst.c   | 30 +++++++++++++++++++
>> >  drivers/gpu/drm/i915/i915_reg.h               |  4 +++
>> >  3 files changed, 36 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
>> > b/drivers/gpu/drm/i915/display/intel_display_types.h
>> > index 17fc21f6ae36..5f151ad9b878 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
>> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
>> > @@ -1770,6 +1770,8 @@ struct intel_dp {
>> >
>> >  	u8 alpm_dpcd;
>> >
>> > +	u32 min_hblank;
>> > +
>> 
>> Why would this be in intel_dp?
>> 
> This feature is part of DP2.1 hence adding in intel_dp struct.
>
>> >  	struct {
>> >  		unsigned long mask;
>> >  	} quirks;
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> > b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> > index 4765bda154c1..45c8be7cd7b3 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> > @@ -156,6 +156,30 @@ static int intel_dp_mst_calc_pbn(int pixel_clock, int
>> bpp_x16, int bw_overhead)
>> >  	return DIV_ROUND_UP(effective_data_rate * 64, 54 * 1000);  }
>> >
>> > +static void intel_dp_mst_compute_min_hblank(struct intel_crtc_state
>> *crtc_state,
>> > +					    struct intel_connector
>> *intel_connector,
>> > +					    int bpp_x16)
>> > +{
>> > +	struct intel_encoder *intel_encoder = intel_connector->encoder;
>> > +	struct intel_dp_mst_encoder *intel_mst = enc_to_mst(intel_encoder);
>> > +	struct intel_dp *intel_dp = &intel_mst->primary->dp;
>> > +	struct intel_display *intel_display = to_intel_display(intel_encoder);
>> > +	const struct drm_display_mode *adjusted_mode =
>> > +					&crtc_state->hw.adjusted_mode;
>> > +	u32 symbol_size = intel_dp_is_uhbr(crtc_state) ? 32 : 8;
>> > +	u32 hblank;
>> > +
>> > +	if (DISPLAY_VER(intel_display) < 20)
>> > +		return;
>> > +
>> > +	/* Calculate min Hblank Link Layer Symbol Cycle Count for 8b/10b MST
>> & 128b/132b */
>> > +	hblank = DIV_ROUND_UP((DIV_ROUND_UP(adjusted_mode->htotal -
>> adjusted_mode->hdisplay, 4) * bpp_x16), symbol_size);
>> > +	if (intel_dp_is_uhbr(crtc_state))
>> > +		intel_dp->min_hblank = hblank > 5 ? hblank : 5;
>> > +	else
>> > +		intel_dp->min_hblank = hblank > 3 ? hblank : 3;
>> 
>> Compute config must not mess with permanent data.
>> 
> Tend to change on mode change. Hence added this in modeset config. This is MST only feature hence added in mst_compute_config.

The point is, compute config must not mess with persistent data, such as
struct intel_dp, so maybe the data should not be part of persistent data
but rather crtc state, with state readout and checks etc.

BR,
Jani.


>
> Thanks and Regards,
> Arun R Murthy
> --------------------
>
>> This should be in crtc state with readout and state checker etc.
>> 
>> BR,
>> Jani.
>> 
>> > +}
>> > +
>> >  static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder
>> *encoder,
>> >  						struct intel_crtc_state
>> *crtc_state,
>> >  						int max_bpp,
>> > @@ -228,6 +252,8 @@ static int
>> intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
>> >  					 link_bpp_x16,
>> >  					 &crtc_state->dp_m_n);
>> >
>> > +		intel_dp_mst_compute_min_hblank(crtc_state, connector,
>> > +link_bpp_x16);
>> > +
>> >  		/*
>> >  		 * The TU size programmed to the HW determines which slots
>> in
>> >  		 * an MTP frame are used for this stream, which needs to
>> match @@
>> > -1274,6 +1300,10 @@ static void intel_mst_enable_dp(struct
>> intel_atomic_state *state,
>> >  			       TRANS_DP2_VFREQ_PIXEL_CLOCK(crtc_clock_hz &
>> 0xffffff));
>> >  	}
>> >
>> > +	if (DISPLAY_VER(dev_priv) >= 20)
>> > +		intel_de_write(dev_priv, DP_MIN_HBLANK_CTL(dev_priv,
>> trans),
>> > +			       intel_dp->min_hblank);
>> > +
>> >  	enable_bs_jitter_was(pipe_config);
>> >
>> >  	intel_ddi_enable_transcoder_func(encoder, pipe_config); diff --git
>> > a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> > index 7396fc630e29..b321d136e1b0 100644
>> > --- a/drivers/gpu/drm/i915/i915_reg.h
>> > +++ b/drivers/gpu/drm/i915/i915_reg.h
>> > @@ -1138,6 +1138,10 @@
>> >  #define _TRANS_MULT_B		0x6102c
>> >  #define TRANS_MULT(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans),
>> _TRANS_MULT_A)
>> >
>> > +#define _DP_MIN_HBLANK_CTL_A	0x600ac
>> > +#define _DP_MIN_HBLANK_CTL_B	0x610ac
>> > +#define DP_MIN_HBLANK_CTL(dev_priv, trans)
>> 	_MMIO_TRANS2(dev_priv, (trans), _DP_MIN_HBLANK_CTL_A)
>> > +
>> >  /* VGA port control */
>> >  #define ADPA			_MMIO(0x61100)
>> >  #define PCH_ADPA                _MMIO(0xe1100)
>> 
>> --
>> Jani Nikula, Intel

-- 
Jani Nikula, Intel