[Intel-gfx] [PATCH v2 6/6] drm/i915/dp_mst: Ensure the DPCD ACT sent flag is cleared before waiting for it

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude at redhat.com>

Thanks for all the subtle fixes for broken MST displays, these are always my
favorite to find :)

On Wed, 2020-06-17 at 00:11 +0300, Imre Deak wrote:
> Atm, we clear the ACT sent flag in the sink's DPCD before updating the
> sink's payload table, along clearing the payload table updated flag.
> The sink is supposed to set this flag once it detects that the source
> has completed the ACT sequence (after detecting the 4 required ACT MTPH
> symbols sent by the source). As opposed to this 2 DELL monitors I have
> set the flag already along the payload table updated flag, which is not
> quite correct.
> 
> To be sure that the sink has detected the ACT MTPH symbols before
> continuing enabling the encoder, clear the ACT sent flag before enabling
> or disabling the transcoder VC payload allocation (which is what starts
> the ACT sequence).
> 
> v2 (Ville):
> - Use the correct bit to clear the flags.
> - Add code comment explaining the clearing semantics of the ACT handled
>   flag.
> 
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: dri-devel at lists.freedesktop.org
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c       | 38 +++++++++++++++++++--
>  drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 ++
>  include/drm/drm_dp_mst_helper.h             |  2 ++
>  3 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index b2f5a84b4cfb..1f5d14128c1a 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4377,6 +4377,41 @@ void drm_dp_mst_deallocate_vcpi(struct
> drm_dp_mst_topology_mgr *mgr,
>  }
>  EXPORT_SYMBOL(drm_dp_mst_deallocate_vcpi);
>  
> +/**
> + * drm_dp_clear_payload_status() - Clears the payload table status flags
> + * @mgr: manager to use
> + *
> + * Clears the payload table ACT handled and table updated flags in the MST
> hub's
> + * DPCD. This function must be called before updating the payload table or
> + * starting the ACT sequence and waiting for the corresponding flags to get
> + * set by the hub.
> + *
> + * Returns:
> + * 0 if the flags got cleared successfully, otherwise a negative error
> code.
> + */
> +int drm_dp_clear_payload_status(struct drm_dp_mst_topology_mgr *mgr)
> +{
> +	int ret;
> +
> +	/*
> +	 * Note that the following is based on the DP Standard stating that
> +	 * writing the DP_PAYLOAD_TABLE_UPDATED bit alone will clear both the
> +	 * DP_PAYLOAD_TABLE_UPDATED and the DP_PAYLOAD_ACT_HANDLED flags. This
> +	 * seems to be also the only way to clear DP_PAYLOAD_ACT_HANDLED.
> +	 */
> +	ret = drm_dp_dpcd_writeb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS,
> +				 DP_PAYLOAD_TABLE_UPDATED);
> +	if (ret < 0) {
> +		DRM_DEBUG_DRIVER("Can't clear the ACT handled/table updated
> flags (%d)\n",
> +				 ret);
> +		return ret;
> +	}
> +	WARN_ON(ret != 1);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_clear_payload_status);
> +
>  static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
>  				     int id, struct drm_dp_payload *payload)
>  {
> @@ -4384,8 +4419,7 @@ static int drm_dp_dpcd_write_payload(struct
> drm_dp_mst_topology_mgr *mgr,
>  	int ret;
>  	int retries = 0;
>  
> -	drm_dp_dpcd_writeb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS,
> -			   DP_PAYLOAD_TABLE_UPDATED);
> +	drm_dp_clear_payload_status(mgr);
>  
>  	payload_alloc[0] = id;
>  	payload_alloc[1] = payload->start_slot;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 9308b5920780..3c4b0fb10d8b 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -323,6 +323,8 @@ static void clear_act_sent(struct intel_dp *intel_dp)
>  
>  	intel_de_write(i915, intel_dp->regs.dp_tp_status,
>  		       DP_TP_STATUS_ACT_SENT);
> +
> +	drm_dp_clear_payload_status(&intel_dp->mst_mgr);
>  }
>  
>  static void wait_for_act_sent(struct intel_dp *intel_dp)
> diff --git a/include/drm/drm_dp_mst_helper.h
> b/include/drm/drm_dp_mst_helper.h
> index 8b9eb4db3381..2facb87624bf 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -763,6 +763,8 @@ int drm_dp_find_vcpi_slots(struct
> drm_dp_mst_topology_mgr *mgr,
>  			   int pbn);
>  
>  
> +int drm_dp_clear_payload_status(struct drm_dp_mst_topology_mgr *mgr);
> +
>  int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr);
>  
>  
-- 
Cheers,
	Lyude Paul (she/her)
	Associate Software Engineer at Red Hat