Re: [Intel-gfx] [PATCH] drm/i915/dsi: let HW maintain HS-TRAIL and CLK_POST

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Sep 01, 2023 at 05:51:00PM +0800, William Tseng wrote:
> This change is to adjust TEOT timing and TCLK-POST timing so DSI
> signaling can meet CTS specification.
> 
> For clock lane, the measured TEOT may be changed from 142.64 ns to
> 107.36 ns, which is less than (105 ns+12*UI) and is conformed to
> mipi D-PHY v1.2 CTS v1.0.
> 
> As to TCLK-POST, it may be changed from 133.44 ns to 178.72 ns, which
> is greater than (60 ns+52*UI) and is conformed to the CTS standard.
> 
> The computed UI is around 1.47 ns.
> 
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
> Cc: Suraj Kandpal <suraj.kandpal@intel.com>
> Cc: Lee Shawn C <shawn.c.lee@intel.com>
> Signed-off-by: William Tseng <william.tseng@intel.com>
> ---
>  drivers/gpu/drm/i915/display/icl_dsi.c | 31 ++++----------------------
>  1 file changed, 4 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
> index ad6488e9c2b2..4a13f467ca46 100644
> --- a/drivers/gpu/drm/i915/display/icl_dsi.c
> +++ b/drivers/gpu/drm/i915/display/icl_dsi.c
> @@ -1819,10 +1819,10 @@ static void icl_dphy_param_init(struct intel_dsi *intel_dsi)
>  	struct intel_connector *connector = intel_dsi->attached_connector;
>  	struct mipi_config *mipi_config = connector->panel.vbt.dsi.config;
>  	u32 tlpx_ns;
> -	u32 prepare_cnt, exit_zero_cnt, clk_zero_cnt, trail_cnt;
> -	u32 ths_prepare_ns, tclk_trail_ns;
> +	u32 prepare_cnt, exit_zero_cnt, clk_zero_cnt;
> +	u32 ths_prepare_ns;
>  	u32 hs_zero_cnt;
> -	u32 tclk_pre_cnt, tclk_post_cnt;
> +	u32 tclk_pre_cnt;
>  
>  	tlpx_ns = intel_dsi_tlpx_ns(intel_dsi);
>  
> @@ -1853,14 +1853,6 @@ static void icl_dphy_param_init(struct intel_dsi *intel_dsi)
>  		clk_zero_cnt = ICL_CLK_ZERO_CNT_MAX;
>  	}
>  
> -	/* trail cnt in escape clocks*/
> -	trail_cnt = DIV_ROUND_UP(tclk_trail_ns, tlpx_ns);
> -	if (trail_cnt > ICL_TRAIL_CNT_MAX) {
> -		drm_dbg_kms(&dev_priv->drm, "trail_cnt out of range (%d)\n",
> -			    trail_cnt);
> -		trail_cnt = ICL_TRAIL_CNT_MAX;
> -	}
> -
>  	/* tclk pre count in escape clocks */
>  	tclk_pre_cnt = DIV_ROUND_UP(mipi_config->tclk_pre, tlpx_ns);
>  	if (tclk_pre_cnt > ICL_TCLK_PRE_CNT_MAX) {
> @@ -1869,15 +1861,6 @@ static void icl_dphy_param_init(struct intel_dsi *intel_dsi)
>  		tclk_pre_cnt = ICL_TCLK_PRE_CNT_MAX;
>  	}
>  
> -	/* tclk post count in escape clocks */
> -	tclk_post_cnt = DIV_ROUND_UP(mipi_config->tclk_post, tlpx_ns);
> -	if (tclk_post_cnt > ICL_TCLK_POST_CNT_MAX) {
> -		drm_dbg_kms(&dev_priv->drm,
> -			    "tclk_post_cnt out of range (%d)\n",
> -			    tclk_post_cnt);
> -		tclk_post_cnt = ICL_TCLK_POST_CNT_MAX;
> -	}
> -
>  	/* hs zero cnt in escape clocks */
>  	hs_zero_cnt = DIV_ROUND_UP(mipi_config->ths_prepare_hszero -
>  				   ths_prepare_ns, tlpx_ns);
> @@ -1902,19 +1885,13 @@ static void icl_dphy_param_init(struct intel_dsi *intel_dsi)
>  			       CLK_ZERO_OVERRIDE |
>  			       CLK_ZERO(clk_zero_cnt) |
>  			       CLK_PRE_OVERRIDE |
> -			       CLK_PRE(tclk_pre_cnt) |
> -			       CLK_POST_OVERRIDE |
> -			       CLK_POST(tclk_post_cnt) |
> -			       CLK_TRAIL_OVERRIDE |
> -			       CLK_TRAIL(trail_cnt));
> +			       CLK_PRE(tclk_pre_cnt));

Windows seems set these overrides:

icl clk DPHY:  PREPARE,ZERO
icl clk DSI:   PREPARE,ZERO
icl data DPHY: PREPARE,ZERO,EXIT
icl data DSI:  PREPARE,ZERO,EXIT

tgl clk DPHY:  PREPARE,ZERO (?)
tgl clk DSI:   PREPARE,ZERO,POST (?)
tgl data DPHY: PREPARE,ZERO,EXIT
tgl data DSI:  PREPARE,ZERO,EXIT

adl clk DPHY:  PREPARE,ZERO (?)      (also PRE for 2.0-2.5 GHz data rate)
adl clk DSI:   PREPARE,ZERO,POST (?) (also PRE for 2.0-2.5 GHz data rate)
adl data DPHY: PREPARE,ZERO,EXIT
adl data DSI : PREPARE,ZERO,EXIT

Didn't see any justification for the weird mismatch between 
DSI vs. DPHY POST override on tgl+.

Anyways, looks like removing TRAIL is not particularly controversial
since Windows also never overrides it. So probably you should split that
up into a separate patch. 

>  
>  	/* data lanes dphy timings */
>  	intel_dsi->dphy_data_lane_reg = (HS_PREPARE_OVERRIDE |
>  					 HS_PREPARE(prepare_cnt) |
>  					 HS_ZERO_OVERRIDE |
>  					 HS_ZERO(hs_zero_cnt) |
> -					 HS_TRAIL_OVERRIDE |
> -					 HS_TRAIL(trail_cnt) |
>  					 HS_EXIT_OVERRIDE |
>  					 HS_EXIT(exit_zero_cnt));
>  
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel