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    SubjectRe: [PATCH 1/4] drm/atomic: integrate modeset lock with private objects
    On Wed, Feb 21, 2018 at 10:20:03AM -0500, Rob Clark wrote:
    > On Wed, Feb 21, 2018 at 10:07 AM, Ville Syrjälä
    > <ville.syrjala@linux.intel.com> wrote:
    > > On Wed, Feb 21, 2018 at 09:54:49AM -0500, Rob Clark wrote:
    > >> On Wed, Feb 21, 2018 at 9:49 AM, Ville Syrjälä
    > >> <ville.syrjala@linux.intel.com> wrote:
    > >> > On Wed, Feb 21, 2018 at 09:37:21AM -0500, Rob Clark wrote:
    > >> >> Follow the same pattern of locking as with other state objects. This
    > >> >> avoids boilerplate in the driver.
    > >> >
    > >> > I'm not sure we really want to do this. What if the driver wants a
    > >> > custom locking scheme for this state?
    > >>
    > >> That seems like something we want to discourage, ie. all the more
    > >> reason for this patch.
    > >>
    > >> There is no reason drivers could not split their global state into
    > >> multiple private objs's, each with their own lock, for more fine
    > >> grained locking. That is basically the only valid reason I can think
    > >> of for "custom locking".
    > >
    > > In i915 we have at least one case that would want something close to an
    > > rwlock. Any crtc lock is enough for read, need all of them for write.
    > > Though if we wanted to use private objs for that we might need to
    > > actually make the states refcounted as well, otherwise I can imagine
    > > we might land in some use-after-free issues once again.
    > >
    > > Maybe we could duplicate the state into per-crtc and global copies, but
    > > then we have to keep all of those in sync somehow which doesn't sound
    > > particularly pleasant.
    >
    > Or just keep your own driver lock for read, and use that plus the core
    > modeset lock for write?

    If we can't add the private obj to the state we can't really use it.

    >
    > BR,
    > -R
    >
    > >
    > >>
    > >> (And ofc drivers could add there own locks in addition to what is done
    > >> by core, but I'd rather look at that on a case by case basis, rather
    > >> than it being part of the boilerplate in each driver.)
    > >>
    > >> BR,
    > >> -R
    > >>
    > >> >>
    > >> >> Signed-off-by: Rob Clark <robdclark@gmail.com>
    > >> >> ---
    > >> >> drivers/gpu/drm/drm_atomic.c | 9 ++++++++-
    > >> >> include/drm/drm_atomic.h | 5 +++++
    > >> >> 2 files changed, 13 insertions(+), 1 deletion(-)
    > >> >>
    > >> >> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
    > >> >> index fc8c4da409ff..004e621ab307 100644
    > >> >> --- a/drivers/gpu/drm/drm_atomic.c
    > >> >> +++ b/drivers/gpu/drm/drm_atomic.c
    > >> >> @@ -1078,6 +1078,8 @@ drm_atomic_private_obj_init(struct drm_private_obj *obj,
    > >> >> {
    > >> >> memset(obj, 0, sizeof(*obj));
    > >> >>
    > >> >> + drm_modeset_lock_init(&obj->lock);
    > >> >> +
    > >> >> obj->state = state;
    > >> >> obj->funcs = funcs;
    > >> >> }
    > >> >> @@ -1093,6 +1095,7 @@ void
    > >> >> drm_atomic_private_obj_fini(struct drm_private_obj *obj)
    > >> >> {
    > >> >> obj->funcs->atomic_destroy_state(obj, obj->state);
    > >> >> + drm_modeset_lock_fini(&obj->lock);
    > >> >> }
    > >> >> EXPORT_SYMBOL(drm_atomic_private_obj_fini);
    > >> >>
    > >> >> @@ -1113,7 +1116,7 @@ struct drm_private_state *
    > >> >> drm_atomic_get_private_obj_state(struct drm_atomic_state *state,
    > >> >> struct drm_private_obj *obj)
    > >> >> {
    > >> >> - int index, num_objs, i;
    > >> >> + int index, num_objs, i, ret;
    > >> >> size_t size;
    > >> >> struct __drm_private_objs_state *arr;
    > >> >> struct drm_private_state *obj_state;
    > >> >> @@ -1122,6 +1125,10 @@ drm_atomic_get_private_obj_state(struct drm_atomic_state *state,
    > >> >> if (obj == state->private_objs[i].ptr)
    > >> >> return state->private_objs[i].state;
    > >> >>
    > >> >> + ret = drm_modeset_lock(&obj->lock, state->acquire_ctx);
    > >> >> + if (ret)
    > >> >> + return ERR_PTR(ret);
    > >> >> +
    > >> >> num_objs = state->num_private_objs + 1;
    > >> >> size = sizeof(*state->private_objs) * num_objs;
    > >> >> arr = krealloc(state->private_objs, size, GFP_KERNEL);
    > >> >> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
    > >> >> index 09076a625637..9ae53b73c9d2 100644
    > >> >> --- a/include/drm/drm_atomic.h
    > >> >> +++ b/include/drm/drm_atomic.h
    > >> >> @@ -218,6 +218,11 @@ struct drm_private_state_funcs {
    > >> >> * &drm_modeset_lock is required to duplicate and update this object's state.
    > >> >> */
    > >> >> struct drm_private_obj {
    > >> >> + /**
    > >> >> + * @lock: Modeset lock to protect the state object.
    > >> >> + */
    > >> >> + struct drm_modeset_lock lock;
    > >> >> +
    > >> >> /**
    > >> >> * @state: Current atomic state for this driver private object.
    > >> >> */
    > >> >> --
    > >> >> 2.14.3
    > >> >>
    > >> >> _______________________________________________
    > >> >> dri-devel mailing list
    > >> >> dri-devel@lists.freedesktop.org
    > >> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
    > >> >
    > >> > --
    > >> > Ville Syrjälä
    > >> > Intel OTC
    > >
    > > --
    > > Ville Syrjälä
    > > Intel OTC

    --
    Ville Syrjälä
    Intel OTC

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