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

[Archit Taneja]

On 02/22/2017 05:31 AM, Pandiyan, Dhinakaran wrote:
> 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));

That would be nice to have.

In the comment: "It does not grab any locks as the caller is expected to
care of any required locking.", you could maybe be a bit more specific
and rephrase it as "the caller needs to grab the &drm_modeset_lock
responsible for protecting the private object state"

Thanks,
Archit

>
>
> -DK
>

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