Re: [PATCH 12/17] drm/i915/ddi: Configure/enable a port in DDI_BUF_CTL via read-modify-write

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

On Wed, 29 Jan 2025, Imre Deak <imre.deak@intel.com> wrote:
> From: Imre Deak <imre.deak@gmail.com>
>
> The various flags in DDI_BUF_CTL must be programmed at different places
> during a modeset. The expected value of the register at any moment is
> cached in the intel_dp::DP variable and the whole register is written
> using this variable. A simpler way would be not maintaining the cached
> value of the register at all and update only specific fields in the
> register via read-modify-write. Some places - like D2D link enabling or
> the port disabling - use RMW already.
>
> Based on the above update the register via RMW during the port
> configuration / enabling as well. After all the places updating
> DDI_BUF_CTL are changed - probably the voltage-swing/pre-emphasis level
> setting is the only one remaining - tracking the register value in
> intel_dp:DP could be removed.
>
> Signed-off-by: Imre Deak <imre.deak@gmail.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index ddb182550ad0f..64c42505f2ad6 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -359,6 +359,10 @@ static void intel_ddi_init_dp_buf_reg(struct intel_encoder *encoder,
>  
>  	if (IS_ALDERLAKE_P(i915) && intel_encoder_is_tc(encoder)) {
>  		intel_dp->DP |= ddi_buf_phy_link_rate(crtc_state->port_clock);
> +		/*
> +		 * TODO: remove the following once DDI_BUF_CTL is updated via
> +		 * an RMW everywhere.
> +		 */
>  		if (!intel_tc_port_in_tbt_alt_mode(dig_port))
>  			intel_dp->DP |= DDI_BUF_CTL_TC_PHY_OWNERSHIP;
>  	}
> @@ -370,6 +374,22 @@ static void intel_ddi_init_dp_buf_reg(struct intel_encoder *encoder,
>  	}
>  }
>  
> +static u32 intel_ddi_buf_ctl_config_mask(struct intel_encoder *encoder)
> +{
> +	struct intel_display *display = to_intel_display(encoder);
> +	u32 mask = DDI_BUF_PORT_REVERSAL | DDI_A_4_LANES |
> +		   DDI_PORT_WIDTH_MASK;

The caller only sets DDI_PORT_WIDTH() for display >= 14.

> +
> +	if (DISPLAY_VER(display) >= 14)
> +		mask |= DDI_BUF_PORT_DATA_MASK;

But doesn't touch this?

> +	if (display->platform.alderlake_p)
> +		mask |= DDI_BUF_PHY_LINK_RATE_MASK;

DDI_BUF_CTL_TC_PHY_OWNERSHIP?

> +	if (IS_DISPLAY_VER(display, 11, 13))
> +		mask |= DDI_BUF_LANE_STAGGER_DELAY_MASK;
> +
> +	return mask;
> +}

I don't know, this patch is incredibly hard to follow.

BR,
Jani.


> +
>  static int icl_calc_tbt_pll_link(struct drm_i915_private *dev_priv,
>  				 enum port port)
>  {
> @@ -3062,7 +3082,8 @@ static void intel_enable_ddi_buf(struct intel_encoder *encoder, u32 buf_ctl)
>  	struct intel_display *display = to_intel_display(encoder);
>  	enum port port = encoder->port;
>  
> -	intel_de_write(display, DDI_BUF_CTL(port), buf_ctl | DDI_BUF_CTL_ENABLE);
> +	intel_de_rmw(display, DDI_BUF_CTL(port),
> +		     intel_ddi_buf_ctl_config_mask(encoder), buf_ctl | DDI_BUF_CTL_ENABLE);
>  	intel_de_posting_read(display, DDI_BUF_CTL(port));
>  
>  	intel_wait_ddi_buf_active(encoder);

-- 
Jani Nikula, Intel