Hi Rob,
On Wednesday 12 September 2012 22:49:47 Rob Clark wrote:
> From: Rob Clark <rob@xxxxxx>
>
> The 'atomic' mechanism allows for multiple properties to be updated,
> checked, and commited atomically. This will be the basis of atomic-
> modeset and nuclear-pageflip.
>
> The basic flow is:
>
> state = dev->atomic_begin();
> for (... one or more ...)
> obj->set_property(obj, state, prop, value);
> if (dev->atomic_check(state))
> dev->atomic_commit(state, event);
> dev->atomic_end(state);
>
> The split of check and commit steps is to allow for ioctls with a
> test-only flag (which would skip the commit step).
>
> The atomic functions are mandatory, as they will end up getting
> called from enough places that it is easier not to have to bother
> with if-null checks everywhere.
>
> TODO:
> + add some stub atomic functions that can be used by drivers
> until they are updated to support atomic operations natively
> + roll-back previous property values if check/commit fails, so
> userspace doesn't see incorrect values.
I have to confess that I have trouble understanding how the various pieces fit
together. The call stacks are quite deep, and pointers to objects are passed
around in a way to makes it difficult to understand what objects are accessed
without going through the whole stack. Reviewing your proposal would be easier
with proper documentation, including a functional overview of the atomic
properties architecture. Renaming some methods would also be worth it:
drm_connector_property_set_value() and drm_mode_connector_set_obj_prop() are
confusing, and I would need pretty long to get used to them without having to
look at the kerneldoc all the time.
Speaking of kerneldoc, there's none :-) Library functions need to be
documented, especially with such a complex code flow.
Before your patches the code currently called the drivers set_property methods
to apply the state to the hardware, and then, if those calls were successful,
called drm_object_property_set_value() to store the property values
permanently.
Your patches modify that behaviour and changes the meaning of set_property.
The method now just updates the new state object without touching the
hardware. However, you still call drm_object_property_set_value() which stores
the new property value in propvals (struct drm_object_property_values).
Rolling back the values is a possible solution. As the mode_config.mutex is
taken around all accesses to propvals, no other thread will be able to access
incorrect values before they're rolled back. However, I wonder whether we
couldn't come up with a more simple solution.
First of all, do we really need dynamic states ? All accesses to properties
are serialized using a single common mutex. We could just have two static
states (current and new) instead of allocating the state at runtime.
Then, do we really need to parse the properties and compute the state values
so early ? We're storing the properties values in two separate locations, in
the propvals structure as "raw" unprocessed values, and also in the state
structures as processed values. Is that really necessary ? Wouldn't it be
simpler to first validate all the new properties and then compute the state
values at commit time ?
I can't really pinpoint the exact reason, but I feel like this is all getting
a bit too messy for my taste. That might be partly caused by me being familiar
with the V4L2 control framework, which solves some of the same issues (such as
modifying several controls atomically) in a (in my opinion) cleaner way. The
problem at hand in DRM might very well be more complex though.
Could you please include more documentation in the next version of this RFC ?
I'd like text documentation that explains the design principles and how the
pieces fit together (including code flows) (in plain text or DocBook, it
doesn't matter much at this point), and kerneldoc for the exported functions.
> ---
> drivers/gpu/drm/drm_crtc.c | 126 +++++++++++++++++++++++++----------------
> include/drm/drmP.h | 52 ++++++++++++++++++
> include/drm/drm_crtc.h | 8 +--
> 3 files changed, 135 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 7552675..3a087cf 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -3227,12 +3227,11 @@ int drm_mode_connector_property_set_ioctl(struct
> drm_device *dev, return drm_mode_obj_set_property_ioctl(dev, &obj_set_prop,
> file_priv); }
>
> -static int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
> - struct drm_property *property,
> +static int drm_mode_connector_set_obj_prop(struct drm_connector *connector,
> + void *state, struct drm_property *property,
> uint64_t value)
> {
> int ret = -EINVAL;
> - struct drm_connector *connector = obj_to_connector(obj);
>
> /* Do DPMS ourselves */
> if (property == connector->dev->mode_config.dpms_property) {
> @@ -3240,7 +3239,7 @@ static int drm_mode_connector_set_obj_prop(struct
> drm_mode_object *obj, (*connector->funcs->dpms)(connector, (int)value);
> ret = 0;
> } else if (connector->funcs->set_property)
> - ret = connector->funcs->set_property(connector, property, value);
> + ret = connector->funcs->set_property(connector, state, property,
value);
>
> /* store the property value if successful */
> if (!ret)
> @@ -3248,36 +3247,87 @@ static int drm_mode_connector_set_obj_prop(struct
> drm_mode_object *obj, return ret;
> }
>
> -static int drm_mode_crtc_set_obj_prop(struct drm_mode_object *obj,
> - struct drm_property *property,
> +static int drm_mode_crtc_set_obj_prop(struct drm_crtc *crtc,
> + void *state, struct drm_property *property,
> uint64_t value)
> {
> int ret = -EINVAL;
> - struct drm_crtc *crtc = obj_to_crtc(obj);
>
> if (crtc->funcs->set_property)
> - ret = crtc->funcs->set_property(crtc, property, value);
> + ret = crtc->funcs->set_property(crtc, state, property, value);
> if (!ret)
> - drm_object_property_set_value(obj, property, value);
> + drm_object_property_set_value(&crtc->base, property, value);
>
> return ret;
> }
>
> -static int drm_mode_plane_set_obj_prop(struct drm_mode_object *obj,
> - struct drm_property *property,
> +static int drm_mode_plane_set_obj_prop(struct drm_plane *plane,
> + void *state, struct drm_property *property,
> uint64_t value)
> {
> int ret = -EINVAL;
> - struct drm_plane *plane = obj_to_plane(obj);
>
> if (plane->funcs->set_property)
> - ret = plane->funcs->set_property(plane, property, value);
> + ret = plane->funcs->set_property(plane, state, property, value);
> if (!ret)
> - drm_object_property_set_value(obj, property, value);
> + drm_object_property_set_value(&plane->base, property, value);
>
> return ret;
> }
>
> +static int drm_mode_set_obj_prop(struct drm_device *dev,
> + struct drm_mode_object *obj, void *state,
> + struct drm_property *property, uint64_t value)
> +{
> + if (drm_property_change_is_valid(property, value)) {
> + switch (obj->type) {
> + case DRM_MODE_OBJECT_CONNECTOR:
> + return drm_mode_connector_set_obj_prop(obj_to_connector(obj),
> + state, property, value);
> + case DRM_MODE_OBJECT_CRTC:
> + return drm_mode_crtc_set_obj_prop(obj_to_crtc(obj),
> + state, property, value);
> + case DRM_MODE_OBJECT_PLANE:
> + return drm_mode_plane_set_obj_prop(obj_to_plane(obj),
> + state, property, value);
> + }
> + }
> +
> + return -EINVAL;
> +}
> +
> +/* call with mode_config mutex held */
> +static int drm_mode_set_obj_prop_id(struct drm_device *dev, void *state,
> + uint32_t obj_id, uint32_t obj_type,
> + uint32_t prop_id, uint64_t value)
> +{
> + struct drm_mode_object *arg_obj;
> + struct drm_mode_object *prop_obj;
> + struct drm_property *property;
> + int i;
> +
> + arg_obj = drm_mode_object_find(dev, obj_id, obj_type);
> + if (!arg_obj)
> + return -EINVAL;
> + if (!arg_obj->properties)
> + return -EINVAL;
> +
> + for (i = 0; i < arg_obj->properties->count; i++)
> + if (arg_obj->properties->ids[i] == prop_id)
> + break;
> +
> + if (i == arg_obj->properties->count)
> + return -EINVAL;
> +
> + prop_obj = drm_mode_object_find(dev, prop_id,
> + DRM_MODE_OBJECT_PROPERTY);
> + if (!prop_obj)
> + return -EINVAL;
> + property = obj_to_property(prop_obj);
> +
> + return drm_mode_set_obj_prop(dev, arg_obj, state, property, value);
> +}
> +
> int drm_mode_obj_get_properties_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_priv)
> {
> @@ -3338,53 +3388,35 @@ int drm_mode_obj_set_property_ioctl(struct
> drm_device *dev, void *data, struct drm_file *file_priv)
> {
> struct drm_mode_obj_set_property *arg = data;
> - struct drm_mode_object *arg_obj;
> - struct drm_mode_object *prop_obj;
> - struct drm_property *property;
> + void *state = NULL;
> int ret = -EINVAL;
> - int i;
>
> if (!drm_core_check_feature(dev, DRIVER_MODESET))
> return -EINVAL;
>
> mutex_lock(&dev->mode_config.mutex);
>
> - arg_obj = drm_mode_object_find(dev, arg->obj_id, arg->obj_type);
> - if (!arg_obj)
> - goto out;
> - if (!arg_obj->properties)
> - goto out;
> -
> - for (i = 0; i < arg_obj->properties->count; i++)
> - if (arg_obj->properties->ids[i] == arg->prop_id)
> - break;
> + state = dev->driver->atomic_begin(dev, NULL);
> + if (IS_ERR(state)) {
> + ret = PTR_ERR(state);
> + goto out_unlock;
> + }
>
> - if (i == arg_obj->properties->count)
> + ret = drm_mode_set_obj_prop_id(dev, state,
> + arg->obj_id, arg->obj_type,
> + arg->prop_id, arg->value);
> + if (ret)
> goto out;
>
> - prop_obj = drm_mode_object_find(dev, arg->prop_id,
> - DRM_MODE_OBJECT_PROPERTY);
> - if (!prop_obj)
> - goto out;
> - property = obj_to_property(prop_obj);
> -
> - if (!drm_property_change_is_valid(property, arg->value))
> + ret = dev->driver->atomic_check(dev, state);
> + if (ret)
> goto out;
>
> - switch (arg_obj->type) {
> - case DRM_MODE_OBJECT_CONNECTOR:
> - ret = drm_mode_connector_set_obj_prop(arg_obj, property,
> - arg->value);
> - break;
> - case DRM_MODE_OBJECT_CRTC:
> - ret = drm_mode_crtc_set_obj_prop(arg_obj, property, arg->value);
> - break;
> - case DRM_MODE_OBJECT_PLANE:
> - ret = drm_mode_plane_set_obj_prop(arg_obj, property, arg->value);
> - break;
> - }
> + ret = dev->driver->atomic_commit(dev, state, NULL);
>
> out:
> + dev->driver->atomic_end(dev, state);
> +out_unlock:
> mutex_unlock(&dev->mode_config.mutex);
> return ret;
> }
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index d6b67bb..f719c4d 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -933,6 +933,58 @@ struct drm_driver {
> struct drm_device *dev,
> uint32_t handle);
>
> + /*
> + * Atomic functions:
> + */
> +
> + /**
> + * Begin a sequence of atomic property sets. Returns a driver
> + * private state object that is passed back into the various
> + * object's set_property() fxns, and into the remainder of the
> + * atomic funcs. The state object should accumulate the changes
> + * from one o more set_property()'s. At the end, the state can
> + * be checked, and optionally committed.
> + *
> + * \param dev dev DRM device handle.
> + * \param crtc for asynchronous page-flip operations, the crtc
> + * that is being updated. (The driver should return -EBUSY if
> + * a page-flip is still pending.) Otherwise, NULL.
> + * \returns a driver private state object, which is passed
> + * back in to the various other atomic fxns
> + */
> + void *(*atomic_begin)(struct drm_device *dev, struct drm_crtc *crtc);
> +
> + /**
> + * Check the state object to see if the requested state is
> + * physically possible.
> + *
> + * \param dev dev DRM device handle.
> + * \param state the driver private state object
> + */
> + int (*atomic_check)(struct drm_device *dev, void *state);
> +
> + /**
> + * Commit the state. This will only be called if atomic_check()
> + * succeeds.
> + *
> + * \param dev dev DRM device handle.
> + * \param state the driver private state object
> + * \param event for asynchronous page-flip operations, the
> + * userspace has requested an event to be sent when the
> + * page-flip completes, or NULL. Will always be NULL for
> + * non-page-flip operations
> + */
> + int (*atomic_commit)(struct drm_device *dev, void *state,
> + struct drm_pending_vblank_event *event);
> +
> + /**
> + * Release resources associated with the state object.
> + *
> + * \param dev dev DRM device handle.
> + * \param state the driver private state object
> + */
> + void (*atomic_end)(struct drm_device *dev, void *state);
> +
> /* Driver private ops for this object */
> const struct vm_operations_struct *gem_vm_ops;
>
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 1422b36..a609190 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -357,7 +357,7 @@ struct drm_crtc_funcs {
> struct drm_framebuffer *fb,
> struct drm_pending_vblank_event *event);
>
> - int (*set_property)(struct drm_crtc *crtc,
> + int (*set_property)(struct drm_crtc *crtc, void *state,
> struct drm_property *property, uint64_t val);
> };
>
> @@ -455,8 +455,8 @@ struct drm_connector_funcs {
> enum drm_connector_status (*detect)(struct drm_connector *connector,
> bool force);
> int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
> uint32_t max_height); - int (*set_property)(struct drm_connector
> *connector, struct drm_property *property, - uint64_t val);
> + int (*set_property)(struct drm_connector *connector, void *state,
> + struct drm_property *property, uint64_t val);
> void (*destroy)(struct drm_connector *connector);
> void (*force)(struct drm_connector *connector);
> };
> @@ -627,7 +627,7 @@ struct drm_plane_funcs {
> int (*disable_plane)(struct drm_plane *plane);
> void (*destroy)(struct drm_plane *plane);
>
> - int (*set_property)(struct drm_plane *plane,
> + int (*set_property)(struct drm_plane *plane, void *state,
> struct drm_property *property, uint64_t val);
> };
--
Regards,
Laurent Pinchart
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