Re: [PATCH 1/3] drm/i915/ddi: add helper to compute DDI clock frequency

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

On Tue, 11 Aug 2026, Suraj Kandpal <suraj.kandpal@intel.com> wrote:
> Add intel_ddi_link_symbol_clock() to return the DDI clock frequency for
> a given port clock:
>   DP 8b/10b : rate / 10

rate

>   DP 128b/132b (UHBR) : rate / 32

(10/32) * rate

>   HDMI FRL  : rate / 18

(10/18) * rate

>   HDMI TMDS : rate

>
> The DP case reuses intel_dp_link_symbol_clock().
> This will help in upcoming commits to decide value to be written
> in DDI_CLK_VALFREQ.
>
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 11 +++++++++++
>  drivers/gpu/drm/i915/display/intel_ddi.h |  1 +
>  2 files changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index bf5788c5bbd3..dd9064592ec9 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -1529,6 +1529,17 @@ int intel_ddi_level(struct intel_encoder *encoder,
>  	return level;
>  }
>  
> +int intel_ddi_link_symbol_clock(struct intel_encoder *encoder, int clock)
> +{
> +	if (intel_encoder_is_dp(encoder))
> +		return intel_dp_link_symbol_clock(clock);
> +
> +	if (intel_hdmi_is_frl(clock))
> +		return DIV_ROUND_CLOSEST(clock * 10, 18);
> +
> +	return clock;
> +}
> +
>  static void
>  hsw_set_signal_levels(struct intel_encoder *encoder,
>  		      const struct intel_crtc_state *crtc_state)
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.h b/drivers/gpu/drm/i915/display/intel_ddi.h
> index 580ecb09b8b6..239d5a403f91 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.h
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.h
> @@ -81,6 +81,7 @@ void intel_ddi_sanitize_encoder_pll_mapping(struct intel_encoder *encoder);
>  int intel_ddi_level(struct intel_encoder *encoder,
>  		    const struct intel_crtc_state *crtc_state,
>  		    int lane);
> +int intel_ddi_link_symbol_clock(struct intel_encoder *encoder, int clock);
>  void intel_ddi_update_active_dpll(struct intel_atomic_state *state,
>  				  struct intel_encoder *encoder,
>  				  struct intel_crtc *crtc);

-- 
Jani Nikula, Intel