[RFC 4/4] drm/i915/display/dp: On LT failure retry LT

[Jani Nikula]

On Tue, 06 Feb 2024, Arun R Murthy <arun.r.murthy at intel.com> wrote:
> On link training failure retry link training with a lesser link
> rate/lane count as specified in the DP spec.
>
> Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index ed7620e7f763..29d785a4b904 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -2502,6 +2502,7 @@ static void mtl_ddi_pre_enable_dp(struct intel_atomic_state *state,
>  				 crtc_state->port_clock,
>  				 crtc_state->lane_count);
>  
> +retry:
>  	/*
>  	 * We only configure what the register value will be here.  Actual
>  	 * enabling happens during link training farther down.
> @@ -2586,7 +2587,14 @@ static void mtl_ddi_pre_enable_dp(struct intel_atomic_state *state,
>  	 *     Pattern, wait for 5 idle patterns (DP_TP_STATUS Min_Idles_Sent)
>  	 *     (timeout after 800 us)
>  	 */
> -	intel_dp_start_link_train(intel_dp, crtc_state);
> +	if (!intel_dp_start_link_train(intel_dp, crtc_state)) {
> +		/* Link Training failed, retain */
> +		intel_dp->link_trained = false;
> +		intel_dp_stop_link_train(intel_dp, crtc_state);
> +		encoder->post_disable(state, encoder,
> +				   crtc_state, conn_state);
> +		goto retry;
> +	}

As said, the retry needs to go via userspace.

BR,
Jani.


>  
>  	/* 6.n Set DP_TP_CTL link training to Normal */
>  	if (!is_trans_port_sync_mode(crtc_state))

-- 
Jani Nikula, Intel