On Mon, 10 Jan 2022, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> On Fri, Dec 31, 2021 at 03:23:31PM +0200, Jani Nikula wrote:
>> On Wed, 12 Jul 2017, ville.syrjala@xxxxxxxxxxxxxxx wrote:
>> > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> >
>> > Make the atomic private object stuff less special by introducing proper
>> > base classes for the object and its state. Drivers can embed these in
>> > their own appropriate objects, after which these things will work
>> > exactly like the plane/crtc/connector states during atomic operations.
>> >
>> > v2: Reorder to not depend on drm_dynarray (Daniel)
>> >
>> > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
>> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
>> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> #v1
>> > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>>
>> Stumbled upon an old commit
>>
>> commit a4370c777406c2810e37fafd166ccddecdb2a60c
>> Author: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> Date: Wed Jul 12 18:51:02 2017 +0300
>>
>> drm/atomic: Make private objs proper objects
>>
>> which is this patch.
>>
>> > @@ -3050,8 +3043,7 @@ struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_a
>> > struct drm_device *dev = mgr->dev;
>> >
>> > WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>> > - return drm_atomic_get_private_obj_state(state, mgr,
>> > - &mst_state_funcs);
>> > + return to_dp_mst_topology_state(drm_atomic_get_private_obj_state(state, &mgr->base));
>> > }
>> > EXPORT_SYMBOL(drm_atomic_get_mst_topology_state);
>>
>> I don't think this combines well with...
>>
>> > diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
>> > index 177ab6f86855..d55abb75f29a 100644
>> > --- a/include/drm/drm_dp_mst_helper.h
>> > +++ b/include/drm/drm_dp_mst_helper.h
>> > @@ -404,12 +404,17 @@ struct drm_dp_payload {
>> > int vcpi;
>> > };
>> >
>> > +#define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base)
>>
>> ...this in case of error pointers that
>> drm_atomic_get_private_obj_state() may return.
>
> offsetof(base)==0 so should work in practice.
Returning zeros is fine, but error pointers are another matter.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
