Re: [Intel-gfx] [PATCH 3/6] drm/i915: Leave intel_conn->mst_port set, use mst_port_gone instead

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Sep 18, 2018 at 07:06:19PM -0400, Lyude Paul wrote:
> Currently we set intel_connector->mst_port to NULL to signify that the
> MST port has been removed from the system so that we can prevent further
> action on the port such as connector probes, mode probing, etc.
> However, we're going to need access to intel_connector->mst_port in
> order to fixup ->best_encoder() so that it can always return the correct
> encoder for an MST port to prevent legacy DPMS prop changes from
> failing. This should be safe, so instead keep intel_connector->mst_port
> always set and instead add intel_connector->mst_port_gone in order to
> signify whether or not the connector has disappeared from the system.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: stable@vger.kernel.org

Hm, how exactly do legacy DPMS setprop blow up here? Or at least I can't
come up with a scenario that's specific to legacy props, atomic should be
equally affected. By the time we land in this code, the core code already
remapping it to be purely an atomic update.

Another thought: Should we handle at least some of this in the probe
helpers? I.e. once you unplugged a drm_connector, it always shows
disconnected and mode list is gone, instead of duplicating this over all
drivers. We could just check connector->registered.

Thanks, Daniel
> ---
>  drivers/gpu/drm/i915/intel_dp_mst.c | 14 +++++++-------
>  drivers/gpu/drm/i915/intel_drv.h    |  1 +
>  2 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 4ecd65375603..fcb9b87b9339 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -311,9 +311,8 @@ static int intel_dp_mst_get_ddc_modes(struct drm_connector *connector)
>  	struct edid *edid;
>  	int ret;
>  
> -	if (!intel_dp) {
> +	if (intel_connector->mst_port_gone)
>  		return intel_connector_update_modes(connector, NULL);
> -	}
>  
>  	edid = drm_dp_mst_get_edid(connector, &intel_dp->mst_mgr, intel_connector->port);
>  	ret = intel_connector_update_modes(connector, edid);
> @@ -328,9 +327,10 @@ intel_dp_mst_detect(struct drm_connector *connector, bool force)
>  	struct intel_connector *intel_connector = to_intel_connector(connector);
>  	struct intel_dp *intel_dp = intel_connector->mst_port;
>  
> -	if (!intel_dp)
> +	if (intel_connector->mst_port_gone)
>  		return connector_status_disconnected;
> -	return drm_dp_mst_detect_port(connector, &intel_dp->mst_mgr, intel_connector->port);
> +	return drm_dp_mst_detect_port(connector, &intel_dp->mst_mgr,
> +				      intel_connector->port);
>  }
>  
>  static void
> @@ -370,7 +370,7 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
>  	int bpp = 24; /* MST uses fixed bpp */
>  	int max_rate, mode_rate, max_lanes, max_link_clock;
>  
> -	if (!intel_dp)
> +	if (intel_connector->mst_port_gone)
>  		return MODE_ERROR;
>  
>  	if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
> @@ -402,7 +402,7 @@ static struct drm_encoder *intel_mst_atomic_best_encoder(struct drm_connector *c
>  	struct intel_dp *intel_dp = intel_connector->mst_port;
>  	struct intel_crtc *crtc = to_intel_crtc(state->crtc);
>  
> -	if (!intel_dp)
> +	if (intel_connector->mst_port_gone)
>  		return NULL;
>  	return &intel_dp->mst_encoders[crtc->pipe]->base.base;
>  }
> @@ -514,7 +514,7 @@ static void intel_dp_destroy_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
>  						   connector);
>  	/* prevent race with the check in ->detect */
>  	drm_modeset_lock(&connector->dev->mode_config.connection_mutex, NULL);
> -	intel_connector->mst_port = NULL;
> +	intel_connector->mst_port_gone = true;
>  	drm_modeset_unlock(&connector->dev->mode_config.connection_mutex);
>  
>  	drm_connector_put(connector);
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 8fc61e96754f..87ce772ae7f8 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -409,6 +409,7 @@ struct intel_connector {
>  	void *port; /* store this opaque as its illegal to dereference it */
>  
>  	struct intel_dp *mst_port;
> +	bool mst_port_gone;
>  
>  	/* Work struct to schedule a uevent on link train failure */
>  	struct work_struct modeset_retry_work;
> -- 
> 2.17.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch