[PATCH 21/28] drm: Kerneldoc for drm_mode_config_funcs

Daniel Vetter
2015-12-04T08:46:40Z

The meat here is definitely the detailed specs for what atomic_check
and atomic_commit are supposed to do.

And another candidate for a core vfunc that should be in a helper really
(output_poll_changed this time around).

v2: Feedback from Eric on irc:
- spelling fixes.
- spec what async should do
- copy the event related paragraphs from page_flip and adjust
- make it clear that a successful async commit is not allowed to leave
the pipe dead or disabled.

v3: Use FIXME comments to annotate functions that we should move to
some helpers.

Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
include/drm/drm_crtc.h | 241 +++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 233 insertions(+), 8 deletions(-)

diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 551484fb55e5..37cff64a26ef 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1715,31 +1715,256 @@ struct drm_mode_set {

/**
* struct drm_mode_config_funcs - basic driver provided mode setting functions
- * @fb_create: create a new framebuffer object
- * @output_poll_changed: function to handle output configuration changes
- * @atomic_check: check whether a given atomic state update is possible
- * @atomic_commit: commit an atomic state update previously verified with
- * atomic_check()
- * @atomic_state_alloc: allocate a new atomic state
- * @atomic_state_clear: clear the atomic state
- * @atomic_state_free: free the atomic state
*
* Some global (i.e. not per-CRTC, connector, etc) mode setting functions that
* involve drivers.
*/
struct drm_mode_config_funcs {
+ /**
+ * @fb_create:
+ *
+ * Create a new framebuffer object. The core does basic checks on the
+ * requested metadata, but most of that is left to the driver. See
+ * struct &drm_mode_fb_cmd2 for details.
+ *
+ * RETURNS:
+ *
+ * A new framebuffer with an initial refernce count of 1 or a negative
+ * error code encoded with ERR_PTR().
+ */
struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
struct drm_file *file_priv,
const struct drm_mode_fb_cmd2 *mode_cmd);
+
+ /**
+ * @output_poll_changed:
+ *
+ * Callback used by helpers to inform the driver of output configuration
+ * changes.
+ *
+ * Drivers implementing fbdev emulation with the helpers can call
+ * drm_fb_helper_hotplug_changed from this hook to inform the fbdev
+ * helper of output changes.
+ *
+ * FIXME:
+ *
+ * Except that there's no vtable for device-level helper callbacks
+ * there's no reason this is a core function.
+ */
void (*output_poll_changed)(struct drm_device *dev);

+ /**
+ * @atomic_check:
+ *
+ * This is the only hook to validate an atomic modeset update. This
+ * function must reject any modeset and state changes which the hardware
+ * or driver doesn't support. This includes but is of course not limited
+ * to:
+ *
+ * - Checking that the modes, framebuffers, scaling and placement
+ * requirements and so on are within the limits of the hardware.
+ *
+ * - Checking that any hidden shared resources are not oversubscribed.
+ * This can be shared PLLs, shared lanes, overall memory bandwidth,
+ * display fifo space (where shared between planes or maybe even
+ * CRTCs).
+ *
+ * - Checking that virtualized resources exported to userspace are not
+ * oversubscribed. For various reasons it can make sense to expose
+ * more planes, crtcs or encoders than which are physically there. One
+ * example is dual-pipe operations (which generally should be hidden
+ * from userspace if when lockstepped in hardware, otherwise exposed),
+ * where a plane might need 1 hardware plane (if it's just on one
+ * pipe), 2 hardware planes (when it spans both pipes) or maybe even
+ * shared a hardware plane with a 2nd plane (if there's a compatible
+ * plane requested on the area handled by the other pipe).
+ *
+ * - Check that any transitional state is possible and that if
+ * requested, the update can indeed be done in the vblank period
+ * without temporarily disabling some functions.
+ *
+ * - Check any other constraints the driver or hardware might have.
+ *
+ * - This callback also needs to correctly fill out the &drm_crtc_state
+ * in this update to make sure that drm_atomic_crtc_needs_modeset()
+ * reflects the nature of the possible update and returns true if and
+ * only if the update cannot be applied without tearing within one
+ * vblank on that CRTC. The core uses that information to reject
+ * updates which require a full modeset (i.e. blanking the screen, or
+ * at least pausing updates for a substantial amount of time) if
+ * userspace has disallowed that in its request.
+ *
+ * - The driver also does not need to repeat basic input validation
+ * like done for the corresponding legacy entry points. The core does
+ * that before calling this hook.
+ *
+ * See the documentation of @atomic_commit for an exhaustive list of
+ * error conditions which are allowed to not be checked in this
+ * callback.
+ *
+ * See the documentation for struct &drm_atomic_state for how exactly
+ * an atomic modeset update is described.
+ *
+ * Drivers using the atomic helpers can implement this hook using
+ * drm_atomic_helper_check(), or one of the exported sub-functions of
+ * it.
+ *
+ * RETURNS:
+ *
+ * 0 on success or one of the below negative error codes:
+ *
+ * - -EINVAL, if any of the above constraints are violated.
+ *
+ * - -EDEADLK, when returned from an attempt to acquire an additional
+ * &drm_modeset_lock through drm_modeset_lock().
+ *
+ * - -ENOMEM, if allocating additional state sub-structures failed due
+ * to lack of memory.
+ *
+ * - -EINTR, -EAGAIN or -ERESTARTSYS, if the ioctl should be restarted.
+ * This can either be due to a pending signal, or because the driver
+ * needs to completely bail out to recover from an exceptional
+ * situation like a gpu hang. From a userspace point all errors are
+ * treated equally.
+ */
int (*atomic_check)(struct drm_device *dev,
struct drm_atomic_state *a);
+
+ /**
+ * @atomic_commit:
+ *
+ * This is the only hook to commit an atomic modeset update. The core
+ * guarantees that @atomic_check has been called successfully before
+ * calling this function, and that nothing has been changed in the
+ * interim.
+ *
+ * See the documentation for struct &drm_atomic_state for how exactly
+ * an atomic modeset update is described.
+ *
+ * Drivers using the atomic helpers can implement this hook using
+ * drm_atomic_helper_commit(), or one of the exported sub-functions of
+ * it.
+ *
+ * Asynchronous commits (as indicated with the async parameter) must
+ * do any preparatory work which might result in an unsuccessful commit
+ * in the context of this callback. The only exception is hardware
+ * errors resulting in -EIO. But even in that case the driver must
+ * ensure that the display pipe is at least running, to avoid
+ * compositors crashing when pageflips don't work. Anything else,
+ * specifically committing the update to the hardware, should be done
+ * without blocking the caller. For updates which do not require a
+ * modeset this must be guaranteed.
+ *
+ * The driver must wait for any pending rendering to the new
+ * framebuffers to complete before executing the flip. It should also
+ * wait for any pending rendering from other drivers if the underlying
+ * buffer is a shared dma-buf. Asynchronous commits must not wait for
+ * rendering in the context of this callback.
+ *
+ * An application can request to be notified when the atomic commit has
+ * completed. These events are per-CRTC and can be distinguished by the
+ * CRTC index supplied in &drm_event to userspace.
+ *
+ * The drm core will supply a struct &drm_event in the event
+ * member of each CRTC's &drm_crtc_state structure. This can be handled by the
+ * drm_crtc_send_vblank_event() function, which the driver should call on
+ * the provided event upon completion of the atomic commit. Note that if
+ * the driver supports vblank signalling and timestamping the vblank
+ * counters and timestamps must agree with the ones returned from page
+ * flip events. With the current vblank helper infrastructure this can
+ * be achieved by holding a vblank reference while the page flip is
+ * pending, acquired through drm_crtc_vblank_get() and released with
+ * drm_crtc_vblank_put(). Drivers are free to implement their own vblank
+ * counter and timestamp tracking though, e.g. if they have accurate
+ * timestamp registers in hardware.
+ *
+ * NOTE:
+ *
+ * Drivers are not allowed to shut down any display pipe successfully
+ * enabled through an atomic commit on their own. Doing so can result in
+ * compositors crashing if a page flip is suddenly reject because the
+ * pipe is off.
+ *
+ * RETURNS:
+ *
+ * 0 on success or one of the below negative error codes:
+ *
+ * - -EBUSY, if an asynchronous updated is requested and there is
+ * currently an earlier updated still pending. Drivers are allowed to
+ * support a queue of outstanding updates, but currently no driver
+ * supports that. Note that drivers must wait for preceding updates
+ * to complete if a synchronous update is requested, they are not
+ * allowed to fail the commit in that case.
+ *
+ * - -ENOMEM, if the driver failed to allocate memory. Specifically
+ * this can happen when trying to pin framebuffers, which must only
+ * be done when committing the state.
+ *
+ * - -ENOSPC, as a refinement of the more generic -ENOMEM to indicate
+ * that the driver has run out of vram, iommu space or similar gpu
+ * address space needed for framebuffer.
+ *
+ * - -EIO, if the hardware completely died.
+ *
+ * - -EINTR, -EAGAIN or -ERESTARTSYS, if the ioctl should be restarted.
+ * This can either be due to a pending signal, or because the driver
+ * needs to completely bail out to recover from an exceptional
+ * situation like a gpu hang. From a userspace point of view all errors are
+ * treated equally.
+ *
+ * This list is exhaustive. Specifically this hook is not allowed to
+ * return -EINVAL (any invalid requests should be caught in
+ * @atomic_check) or -EDEADLK (this function must not acquire
+ * additional modeset locks). The core will also reject any async
+ * atomic flips with -EINVAL already (for matching semantics in this
+ * case with legacy page flips).
+ */
int (*atomic_commit)(struct drm_device *dev,
struct drm_atomic_state *a,
bool async);
+
+ /**
+ * @atomic_state_alloc:
+ *
+ * This optional hook can be used by drivers who want to subclass struct
+ * &drm_atomic_state to be able to track their own driver-private global
+ * state easily. If this hook is implemented, drivers must also
+ * implement @atomic_state_clear and @atomic_state_free.
+ *
+ * RETURNS:
+ *
+ * A new &drm_atomic_state on success or NULL on failure.
+ */
struct drm_atomic_state *(*atomic_state_alloc)(struct drm_device *dev);
+
+ /**
+ * @atomic_state_clear:
+ *
+ * This hook must clear any driver private state duplicated into the
+ * passed-in &drm_atomic_state. This hook is called when the caller
+ * encountered a &drm_modeset_lock deadlock and needs to drop all
+ * already acquired locks as part of the deadlock avoidance dance
+ * implemented in drm_modeset_lock_backoff().
+ *
+ * Any duplicated state must be invalidated since a concurrent atomic
+ * update might change it, and the drm atomic interfaces always apply
+ * updates as relative changes to the current state.
+ *
+ * Drivers who implement this must call drm_atomic_state_default_clear()
+ * to clear common state.
+ */
void (*atomic_state_clear)(struct drm_atomic_state *state);
+
+ /**
+ * @atomic_state_free:
+ *
+ * This hook needs driver private resources and the &drm_atomic_state
+ * itself. Note that the core first calls drm_atomic_state_clear to
+ * avoid code duplicate between the clear and free hooks.
+ *
+ * Drivers who implement this must call drm_atomic_state_default_free()
+ * to release common resources.
+ */
void (*atomic_state_free)(struct drm_atomic_state *state);
};

--
2.5.1