Re: [PATCH 4/6] drm/dp: Introduce DP MST topology manager state to track DP link bw

From: Daniel Vetter <daniel@ffwll.ch>
To: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 4/6] drm/dp: Introduce DP MST topology manager state to track DP link bw
Date: Wed, 4 Jan 2017 10:33:52 +0100	[thread overview]
Message-ID: <20170104093352.kwlzqyjp4ylam6x6@phenom.ffwll.local> (raw)
In-Reply-To: <1483477311-3511-5-git-send-email-dhinakaran.pandiyan@intel.com>

On Tue, Jan 03, 2017 at 01:01:49PM -0800, Dhinakaran Pandiyan wrote:
> Link bandwidth is shared between multiple display streams in DP MST
> configurations. The DP MST topology manager structure maintains the shared
> link bandwidth for a primary link directly connected to the GPU. For atomic
> modesetting drivers, checking if there is sufficient link bandwidth for a
> mode needs to be done during the atomic_check phase to avoid failed
> modesets. Let's encsapsulate the available link bw information in a state
> structure so that bw can be allocated and released atomically for each of
> the ports sharing the primary link.
> 
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

Overall issue with the patch is that dp helpers now have 2 places where
available_slots is stored: One for atomic drivers in ->state, and the
legacy one. I think it'd be good to rework the legacy codepaths (i.e.
drm_dp_find_vcpi_slots) to use mgr->state->avail_slots, and remove
mgr->avail_slots entirely.

Another design concern below, but in principle this looks like what we
need.
-Daniel

> ---
>  drivers/gpu/drm/drm_atomic.c          | 66 +++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_atomic_helper.c   | 10 ++++++
>  drivers/gpu/drm/drm_dp_mst_topology.c | 10 ++++++
>  include/drm/drm_atomic.h              | 13 +++++++
>  include/drm/drm_dp_mst_helper.h       | 13 +++++++
>  5 files changed, 112 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 681d5f9..b8e2cea 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -31,6 +31,7 @@
>  #include <drm/drm_mode.h>
>  #include <drm/drm_plane_helper.h>
>  #include <drm/drm_print.h>
> +#include <drm/drm_dp_mst_helper.h>
>  #include <linux/sync_file.h>
>  
>  #include "drm_crtc_internal.h"
> @@ -62,6 +63,7 @@ void drm_atomic_state_default_release(struct drm_atomic_state *state)
>  	kfree(state->connectors);
>  	kfree(state->crtcs);
>  	kfree(state->planes);
> +	kfree(state->dp_mst_topologies);
>  }
>  EXPORT_SYMBOL(drm_atomic_state_default_release);
>  
> @@ -189,6 +191,18 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
>  		state->planes[i].ptr = NULL;
>  		state->planes[i].state = NULL;
>  	}
> +
> +	for (i = 0; i < state->num_mst_topologies; i++) {
> +		struct drm_dp_mst_topology_mgr *mgr = state->dp_mst_topologies[i].ptr;
> +
> +		if (!mgr)
> +			continue;
> +
> +		kfree(state->dp_mst_topologies[i].state);
> +		state->dp_mst_topologies[i].ptr = NULL;
> +		state->dp_mst_topologies[i].state = NULL;
> +	}
> +
>  }
>  EXPORT_SYMBOL(drm_atomic_state_default_clear);
>  
> @@ -981,6 +995,58 @@ static void drm_atomic_plane_print_state(struct drm_printer *p,
>  		plane->funcs->atomic_print_state(p, state);
>  }
>  
> +struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
> +		struct drm_dp_mst_topology_mgr *mgr)
> +{
> +
> +	int ret, i;
> +	size_t new_size;
> +	struct __drm_dp_mst_topology_state *new_arr;
> +	struct drm_dp_mst_topology_state *new_mst_state;
> +	int num_topologies;
> +	struct drm_mode_config *config = &mgr->dev->mode_config;
> +
> +	WARN_ON(!state->acquire_ctx);
> +
> +	ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	for (i = 0; i < state->num_mst_topologies; i++) {
> +		if (mgr == state->dp_mst_topologies[i].ptr &&
> +		    state->dp_mst_topologies[i].state) {
> +			return state->dp_mst_topologies[i].state;
> +		}
> +	}
> +
> +	num_topologies = state->num_mst_topologies + 1;
> +	new_size = sizeof(*state->dp_mst_topologies) * num_topologies;
> +	new_arr = krealloc(state->dp_mst_topologies, new_size, GFP_KERNEL);
> +	if (!new_arr)
> +		return ERR_PTR(-ENOMEM);
> +
> +	state->dp_mst_topologies = new_arr;
> +	memset(&state->dp_mst_topologies[state->num_mst_topologies], 0,
> +		sizeof(*state->dp_mst_topologies));
> +
> +	new_mst_state = kmalloc(sizeof(*mgr->state), GFP_KERNEL);
> +	if (!new_mst_state)
> +		return ERR_PTR(-ENOMEM);
> +
> +	new_mst_state->avail_slots = mgr->state->avail_slots;
> +	state->dp_mst_topologies[state->num_mst_topologies].state = new_mst_state;
> +	state->dp_mst_topologies[state->num_mst_topologies].ptr = mgr;
> +	state->num_mst_topologies = num_topologies;
> +	new_mst_state->mgr = mgr;
> +	mgr->state->state = state;
> +
> +	DRM_DEBUG_ATOMIC("Added [MST Topology w/ base connector:%d] %p state to %p\n",
> +			 mgr->conn_base_id, new_mst_state, state);
> +
> +	return new_mst_state;
> +}
> +EXPORT_SYMBOL(drm_atomic_get_mst_topology_state);
> +
>  /**
>   * drm_atomic_get_connector_state - get connector state
>   * @state: global atomic state object
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 5e52244..1cd38b7 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -30,6 +30,7 @@
>  #include <drm/drm_plane_helper.h>
>  #include <drm/drm_crtc_helper.h>
>  #include <drm/drm_atomic_helper.h>
> +#include <drm/drm_dp_mst_helper.h>
>  #include <linux/dma-fence.h>
>  
>  #include "drm_crtc_internal.h"
> @@ -1992,6 +1993,15 @@ void drm_atomic_helper_swap_state(struct drm_atomic_state *state,
>  		connector->state->state = NULL;
>  	}
>  
> +	for (i = 0; i < state->num_mst_topologies; i++) {
> +		struct drm_dp_mst_topology_mgr *mgr;
> +
> +		mgr = state->dp_mst_topologies[i].ptr;
> +		mgr->state->state = state;
> +		swap(state->dp_mst_topologies[i].state, mgr->state);
> +		mgr->state->state = NULL;
> +	}

I'm not sure we want to tie the dp mst helpers that closely with the
atomic machinery, otoh it makes things a lot easier. My concern is that
drm_atomic_state is a core structure, whereas the dp_mst stuff is a
helper, which means we have a control inversion here compared to the
normal pattern.

> +
>  	for_each_crtc_in_state(state, crtc, crtc_state, i) {
>  		crtc->state->state = state;
>  		swap(state->crtcs[i].state, crtc->state);
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index d42a6c0..1be19e1 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2042,6 +2042,9 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
>  			goto out_unlock;
>  		}
>  
> +		/* max. time slots - one slot for MTP header */
> +		mgr->state->avail_slots = 63;
> +
>  		/* add initial branch device at LCT 1 */
>  		mstb = drm_dp_add_mst_branch_device(1, NULL);
>  		if (mstb == NULL) {
> @@ -2973,6 +2976,11 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
>  	mgr->proposed_vcpis = kcalloc(max_payloads, sizeof(struct drm_dp_vcpi *), GFP_KERNEL);
>  	if (!mgr->proposed_vcpis)
>  		return -ENOMEM;
> +	mgr->state = kzalloc(sizeof(*mgr->state), GFP_KERNEL);
> +	if (!mgr->state)
> +		return -ENOMEM;
> +	mgr->state->mgr = mgr;
> +
>  	set_bit(0, &mgr->payload_mask);
>  	if (test_calc_pbn_mode() < 0)
>  		DRM_ERROR("MST PBN self-test failed\n");
> @@ -2995,6 +3003,8 @@ void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
>  	kfree(mgr->proposed_vcpis);
>  	mgr->proposed_vcpis = NULL;
>  	mutex_unlock(&mgr->payload_lock);
> +	kfree(mgr->state);
> +	mgr->state = NULL;
>  	mgr->dev = NULL;
>  	mgr->aux = NULL;
>  }
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index fd2d971..7ac5ed6 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -153,6 +153,11 @@ struct __drm_connnectors_state {
>  	struct drm_connector_state *state;
>  };
>  
> +struct __drm_dp_mst_topology_state {
> +	struct drm_dp_mst_topology_mgr *ptr;
> +	struct drm_dp_mst_topology_state *state;

One way to fix that control inversion I mentioned above is to use void*
pionters here, and then have callbacks for atomic_destroy and swap_state
on top. A bit more shuffling, but we could then use that for other driver
private objects.

Other option is to stuff it into intel_atomic_state.

> +};
> +
>  /**
>   * struct drm_atomic_state - the global state object for atomic updates
>   * @ref: count of all references to this state (will not be freed until zero)
> @@ -164,6 +169,8 @@ struct __drm_connnectors_state {
>   * @crtcs: pointer to array of CRTC pointers
>   * @num_connector: size of the @connectors and @connector_states arrays
>   * @connectors: pointer to array of structures with per-connector data
> + * @num_mst_topologies: size of the @dp_mst_topologies array
> + * @dp_mst_topologies: pointer to array of structures with per-MST topology manager data
>   * @acquire_ctx: acquire context for this atomic modeset state update
>   */
>  struct drm_atomic_state {
> @@ -177,6 +184,8 @@ struct drm_atomic_state {
>  	struct __drm_crtcs_state *crtcs;
>  	int num_connector;
>  	struct __drm_connnectors_state *connectors;
> +	int num_mst_topologies;
> +	struct __drm_dp_mst_topology_state *dp_mst_topologies;
>  
>  	struct drm_modeset_acquire_ctx *acquire_ctx;
>  
> @@ -250,6 +259,10 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		struct drm_connector_state *state, struct drm_property *property,
>  		uint64_t val);
>  
> +struct drm_dp_mst_topology_state * __must_check
> +drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
> +				  struct drm_dp_mst_topology_mgr *mgr);
> +
>  /**
>   * drm_atomic_get_existing_crtc_state - get crtc state, if it exists
>   * @state: global atomic state object
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 98d3c73..0a9bf20 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -403,6 +403,12 @@ struct drm_dp_payload {
>  	int vcpi;
>  };
>  
> +struct drm_dp_mst_topology_state {
> +	int avail_slots;
> +	struct drm_atomic_state *state;
> +	struct drm_dp_mst_topology_mgr *mgr;
> +};
> +
>  /**
>   * struct drm_dp_mst_topology_mgr - DisplayPort MST manager
>   *
> @@ -481,6 +487,11 @@ struct drm_dp_mst_topology_mgr {
>  	int pbn_div;
>  
>  	/**
> +	 *  @state: MST topology manager state for atomic modesetting drivers
> +	 */
> +	struct drm_dp_mst_topology_state *state;
> +
> +	/**
>  	 * @qlock: protects @tx_msg_downq, the tx_slots in struct
>  	 * &drm_dp_mst_branch and txmsg->state once they are queued
>  	 */
> @@ -596,4 +607,6 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
>  
>  void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr);
>  int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
> +struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
> +					struct drm_dp_mst_topology_mgr *mgr);
>  #endif
> -- 
> 2.7.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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