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

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

On Fri, 01 Sep 2023, William Tseng <william.tseng@intel.com> 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.

The question is, why does the VBT define all this stuff, and when should
it be used and when ignored?

Also, this won't build.

BR,
Jani.


>
> 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));
>  
>  	/* 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));

-- 
Jani Nikula, Intel Open Source Graphics Center