[Intel-gfx] [PATCH v3 4/8] drm: Add driver-private objects to atomic state

[Pandiyan, Dhinakaran]

On Fri, 2017-02-17 at 15:37 +0530, Archit Taneja wrote:
> 
> On 02/16/2017 05:43 AM, Pandiyan, Dhinakaran wrote:
> > On Wed, 2017-02-15 at 16:53 +0530, Archit Taneja wrote:
> >> Hi,
> >>
> >> On 02/09/2017 12:08 PM, Dhinakaran Pandiyan wrote:
> >>> It is necessary to track states for objects other than connector, crtc
> >>> and plane for atomic modesets. But adding objects like DP MST link
> >>> bandwidth to drm_atomic_state would mean that a non-core object will be
> >>> modified by the core helper functions for swapping and clearing
> >>> it's state. So, lets add void * objects and helper functions that operate
> >>> on void * types to keep these objects and states private to the core.
> >>> Drivers can then implement specific functions to swap and clear states.
> >>> The other advantage having just void * for these objects in
> >>> drm_atomic_state is that objects of different types can be managed in the
> >>> same state array.
> >>>
> >>> v2: Added docs and new iterator to filter private objects (Daniel)
> >>>
> >>> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >>> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> >>> ---
> >>>  drivers/gpu/drm/drm_atomic.c        | 68 +++++++++++++++++++++++++++
> >>>  drivers/gpu/drm/drm_atomic_helper.c |  5 ++
> >>>  include/drm/drm_atomic.h            | 91 +++++++++++++++++++++++++++++++++++++
> >>>  3 files changed, 164 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> >>> index a567310..1a9ffe8 100644
> >>> --- a/drivers/gpu/drm/drm_atomic.c
> >>> +++ b/drivers/gpu/drm/drm_atomic.c
> >>> @@ -57,6 +57,7 @@ void drm_atomic_state_default_release(struct drm_atomic_state *state)
> >>>  	kfree(state->connectors);
> >>>  	kfree(state->crtcs);
> >>>  	kfree(state->planes);
> >>> +	kfree(state->private_objs);
> >>>  }
> >>>  EXPORT_SYMBOL(drm_atomic_state_default_release);
> >>>
> >>> @@ -184,6 +185,20 @@ 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_private_objs; i++) {
> >>> +		void *private_obj = state->private_objs[i].obj;
> >>> +		void *obj_state = state->private_objs[i].obj_state;
> >>> +
> >>> +		if (!private_obj)
> >>> +			continue;
> >>> +
> >>> +		state->private_objs[i].funcs->destroy_state(obj_state);
> >>> +		state->private_objs[i].obj = NULL;
> >>> +		state->private_objs[i].obj_state = NULL;
> >>> +		state->private_objs[i].funcs = NULL;
> >>> +	}
> >>> +
> >>>  }
> >>>  EXPORT_SYMBOL(drm_atomic_state_default_clear);
> >>>
> >>> @@ -974,6 +989,59 @@ static void drm_atomic_plane_print_state(struct drm_printer *p,
> >>>  }
> >>>
> >>>  /**
> >>> + * drm_atomic_get_private_obj_state - get private object state
> >>> + * @state: global atomic state
> >>> + * @obj: private object to get the state for
> >>> + * @funcs: pointer to the struct of function pointers that identify the object
> >>> + * type
> >>> + *
> >>> + * This function returns the private object state for the given private object,
> >>> + * allocating the state if needed. It does not grab any locks as the caller is
> >>> + * expected to care of any required locking.
> >>> + *
> >>> + * RETURNS:
> >>> + *
> >>> + * Either the allocated state or the error code encoded into a pointer.
> >>> + */
> >>> +void *
> >>> +drm_atomic_get_private_obj_state(struct drm_atomic_state *state, void *obj,
> >>> +			      const struct drm_private_state_funcs *funcs)
> >>> +{
> >>> +	int index, num_objs, i;
> >>> +	size_t size;
> >>> +	struct __drm_private_objs_state *arr;
> >>> +
> >>> +	for (i = 0; i < state->num_private_objs; i++)
> >>> +		if (obj == state->private_objs[i].obj &&
> >>> +		    state->private_objs[i].obj_state)
> >>> +			return state->private_objs[i].obj_state;
> >>
> >> Comparing this func to drm_atomic_get_plane_state/drm_atomic_get_crtc_state, it
> >> doesn't seem to call drm_modeset_lock if the obj_state doesn't already exist. I
> >> don't understand the locking stuff toowell, I just noticed this difference when
> >> comparing this approach with what is done in the msm kms driver (where we
> >> have subclassed drm_atomic_state to msm_kms_state).
> >>
> >> Thanks,
> >> Archit
> >>
> >
> >
> > The caller is expected to take care of any required locking. The
> > driver-private objects are opaque from core's pov, so the core is not
> > aware of necessary locks for that object type.
> 
> I had a look at the rest of the series, and I couldn't easily understand
> whether the caller code protects the MST related driver private state. Is
> it expected to be protect via the drm_mode_config.connection_mutex lock?
> 
> Thanks,
> Archit
> 

That's right, the connection_mutex takes care of the locking for the MST
private state. I can add that as a comment to the caller's (MST helper)
kernel doc with a

WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)); 
 

-DK