[PATCH v4] drm/i915/dsi: let HW maintain the HS-TRAIL timing

[Jani Nikula]

On Tue, 11 Mar 2025, William Tseng <william.tseng at intel.com> wrote:
> This change is to avoid over-specification of the TEOT timing
> parameter, which is derived from software in current design.
>
> Supposed that THS-TRAIL and THS-EXIT have the minimum values,
> i.e., 60 and 100 in ns. If SW is overriding the HW default,
> the TEOT value becomes 150 ns, approximately calculated by
> the following formula.
>
>   DIV_ROUND_UP(60/50)*50 + DIV_ROUND_UP(100/50))*50/2, where 50
>   is LP Escape Clock time in ns.
>
> The TEOT value 150 ns is larger than the maximum value,
> around 136 ns if UI is 1.8ns, (105 ns + 12*UI, defined by MIPI
> DPHY specification).
>
> However, the TEOT value will meet the specification if THS-TRAIL
> is set to the HW default, instead of software overriding.
>
> The timing change is made for both data lane and clock lane.
>
> v1: initial version.
> v2: change clock lane dphy timings.
> v3: remove calculation of trail cnt.
> v4: rebase.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13891
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Vandita Kulkarni <vandita.kulkarni at intel.com>
> Cc: Lee Shawn C <shawn.c.lee at intel.com>
> Cc: Cooper Chiou <cooper.chiou at intel.com>
> Signed-off-by: William Tseng <william.tseng at intel.com>
> Acked-by: Vandita Kulkarni <vandita.kulkarni at intel.com>

Pushed to drm-intel-next. Thanks for the patch, and sorry for the delay.

BR,
Jani.

> ---
>  drivers/gpu/drm/i915/display/icl_dsi.c | 19 +++----------------
>  1 file changed, 3 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
> index 82bf6c654de2..6cf9c9275031 100644
> --- a/drivers/gpu/drm/i915/display/icl_dsi.c
> +++ b/drivers/gpu/drm/i915/display/icl_dsi.c
> @@ -1846,14 +1846,13 @@ 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;
>  
>  	tlpx_ns = intel_dsi_tlpx_ns(intel_dsi);
>  
> -	tclk_trail_ns = max(mipi_config->tclk_trail, mipi_config->ths_trail);
>  	ths_prepare_ns = max(mipi_config->ths_prepare,
>  			     mipi_config->tclk_prepare);
>  
> @@ -1880,14 +1879,6 @@ 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(display->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) {
> @@ -1920,17 +1911,13 @@ 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_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