[PATCH 27/28] drm: Document drm_encoder/crtc_helper_funcs

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

Mostly this is about all the callbacks used to modesets by both legacy
CRTC helpers and atomic helpers and I figured it doesn't make all that
much sense to split this up.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
include/drm/drm_modeset_helper_vtables.h | 447 +++++++++++++++++++++++++++----
1 file changed, 400 insertions(+), 47 deletions(-)

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 22cc51b278fb..d776ef6dd00e 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -46,58 +46,236 @@ enum mode_set_atomic;

/**
* struct drm_crtc_helper_funcs - helper operations for CRTCs
- * @dpms: set power state
- * @prepare: prepare the CRTC, called before @mode_set
- * @commit: commit changes to CRTC, called after @mode_set
- * @mode_fixup: try to fixup proposed mode for this CRTC
- * @mode_set: set this mode
- * @mode_set_nofb: set mode only (no scanout buffer attached)
- * @mode_set_base: update the scanout buffer
- * @mode_set_base_atomic: non-blocking mode set (used for kgdb support)
- * @load_lut: load color palette
- * @disable: disable CRTC when no longer in use
- * @enable: enable CRTC
*
- * The helper operations are called by the mid-layer CRTC helper.
- *
- * Note that with atomic helpers @dpms, @prepare and @commit hooks are
- * deprecated. Used @enable and @disable instead exclusively.
- *
- * With legacy crtc helpers there's a big semantic difference between @disable
- * and the other hooks: @disable also needs to release any resources acquired in
- * @mode_set (like shared PLLs).
+ * These hooks are used by the legacy CRTC helpers, the transitional plane
+ * helpers and the new atomic modesetting helpers.
*/
struct drm_crtc_helper_funcs {
- /*
- * Control power levels on the CRTC. If the mode passed in is
- * unsupported, the provider must use the next lowest power level.
+ /**
+ * @dpms:
+ *
+ * Callback to control power levels on the CRTC. If the mode passed in
+ * is unsupported, the provider must use the next lowest power level.
+ * This is used by the legacy CRTC helpers to implement DPMS
+ * functionality in drm_helper_connector_dpms().
+ *
+ * This callback is also used to disable a CRTC by calling it with
+ * DRM_MODE_DPMS_OFF if the @disable hook isn't used.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for enabling and disabling a CRTC to
+ * facilitate transitions to atomic, but it is deprecated. Instead
+ * @enable and @disable should be used.
*/
void (*dpms)(struct drm_crtc *crtc, int mode);
+
+ /**
+ * @prepare:
+ *
+ * This callback should prepare the CRTC for a subsequent modeset, which
+ * in practice means the driver should disable the CRTC if it is
+ * running. Most drivers ended up implementing this by calling their
+ * @dpms hook with DRM_MODE_DPMS_OFF.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for disabling a CRTC to facilitate
+ * transitions to atomic, but it is deprecated. Instead @disable should
+ * be used.
+ */
void (*prepare)(struct drm_crtc *crtc);
+
+ /**
+ * @commit:
+ *
+ * This callback should commit the new mode on the CRTC after a modeset,
+ * which in practice means the driver should enable the CRTC. Most
+ * drivers ended up implementing this by calling their @dpms hook with
+ * DRM_MODE_DPMS_ON.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for enabling a CRTC to facilitate
+ * transitions to atomic, but it is deprecated. Instead @enable should
+ * be used.
+ */
void (*commit)(struct drm_crtc *crtc);

- /* Provider can fixup or change mode timings before modeset occurs */
+ /**
+ * @mode_fixup:
+ *
+ * This callback is used to validate a mode. The paramater mode is the
+ * display mode that userspace requested, adjusted_mode is the mode the
+ * encoders need to be fed with. Note that this is the inverse semantics
+ * of the meaning for the &drm_encoder and &drm_bridge
+ * ->mode_fixup() functions. If the CRTC cannot support the requested
+ * conversion from mode to adjusted_mode it should reject the modeset.
+ *
+ * This function is used by both legacy CRTC helpers and atomic helpers.
+ * With atomic helpers it is optional.
+ *
+ * NOTE:
+ *
+ * This function is called in the check phase of atomic modesets, which
+ * can be aborted for any reason (including on userspace's request to
+ * just check whether a configuration would be possible). Atomic drivers
+ * MUST NOT touch any persistent state (hardware or software) or data
+ * structures except the passed in adjusted_mode parameter.
+ *
+ * This is in contrast to the legacy CRTC helpers where this was
+ * allowed.
+ *
+ * Atomic drivers which need to inspect and adjust more state should
+ * instead use the @atomic_check callback.
+ *
+ * RETURNS:
+ *
+ * True if an acceptable configuration is possible, false if the modeset
+ * operation should be rejected.
+ */
bool (*mode_fixup)(struct drm_crtc *crtc,
const struct drm_display_mode *mode,
struct drm_display_mode *adjusted_mode);
- /* Actually set the mode */
+
+ /**
+ * @mode_set:
+ *
+ * This callback is used by the legacy CRTC helpers to set a new mode,
+ * position and framebuffer. Since it ties the primary plane to every
+ * mode change it is incompatible with universal plane support. And
+ * since it can't update other planes it's incompatible with atomic
+ * modeset support.
+ *
+ * This callback is only used by CRTC helpers and deprecated.
+ *
+ * RETURNS:
+ *
+ * 0 on success or a negative error code on failure.
+ */
int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
struct drm_display_mode *adjusted_mode, int x, int y,
struct drm_framebuffer *old_fb);
- /* Actually set the mode for atomic helpers, optional */
+
+ /**
+ * @mode_set_nofb:
+ *
+ * This callback is used to update the display mode of a CRTC without
+ * changing anything of the primary plane configuration. This fits the
+ * requirement of atomic and hence is used by the atomic helpers. It is
+ * also used by the transitional plane helpers to implement a
+ * @mode_set hook in drm_helper_crtc_mode_set().
+ *
+ * Note that the display pipe is completely off when this function is
+ * called. Atomic drivers which need hardware to be running before they
+ * program the new display mode (e.g. because they implement runtime PM)
+ * should not use this hook. This is because the helper library calls
+ * this hook only once per mode change and not every time the display
+ * pipeline is suspended using either DPMS or the new "ACTIVE" property.
+ * Which means register values set in this callback might get reset when
+ * the CRTC is suspended, but not restored. Such drivers should instead
+ * move all their CRTC setup into the @enable callback.
+ *
+ * This callback is optional.
+ */
void (*mode_set_nofb)(struct drm_crtc *crtc);

- /* Move the crtc on the current fb to the given position *optional* */
+ /**
+ * @mode_set_base:
+ *
+ * This callback is used by the legacy CRTC helpers to set a new
+ * framebuffer and scanout position. It is optional and used as an
+ * optimized fast-path instead of a full mode set operation with all the
+ * resulting flickering. Since it can't update other planes it's
+ * incompatible with atomic modeset support.
+ *
+ * This callback is only used by the CRTC helpers and deprecated.
+ *
+ * RETURNS:
+ *
+ * 0 on success or a negative error code on failure.
+ */
int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
struct drm_framebuffer *old_fb);
+
+ /**
+ * @mode_set_base_atomic:
+ *
+ * This callback is used by the fbdev helpers to set a new framebuffer
+ * and scanout without sleeping, i.e. from an atomic calling context. It
+ * is only used to implement kgdb support.
+ *
+ * This callback is optional and only needed for kgdb support in the fbdev
+ * helpers.
+ *
+ * RETURNS:
+ *
+ * 0 on success or a negative error code on failure.
+ */
int (*mode_set_base_atomic)(struct drm_crtc *crtc,
struct drm_framebuffer *fb, int x, int y,
enum mode_set_atomic);

- /* reload the current crtc LUT */
+ /**
+ * @load_lut:
+ *
+ * Load a LUT prepared with the @gamma_set functions from
+ * &drm_fb_helper_funcs.
+ *
+ * This callback is optional and is only used by the fbdev emulation
+ * helpers.
+ *
+ * FIXME:
+ *
+ * This callback is functionally redundant with the core gamma table
+ * support and simply exists because the fbdev hasn't yet been
+ * refactored to use the core gamma table interfaces.
+ */
void (*load_lut)(struct drm_crtc *crtc);

+ /**
+ * @disable:
+ *
+ * This callback should be used to disable the CRTC. With the atomic
+ * drivers it is called after all encoders connected to this CRTC have
+ * been shut off already using their own ->disable hook. If that
+ * sequence is too simple drivers can just add their own hooks and call
+ * it from this CRTC callback here by looping over all encoders
+ * connected to it using for_each_encoder_on_crtc().
+ *
+ * This hook is used both by legacy CRTC helpers and atomic helpers.
+ * Atomic drivers don't need to implement it if there's no need to
+ * disable anything at the CRTC level. To ensure that runtime PM
+ * handling (using either DPMS or the new "ACTIVE" property) works
+ * @disable must be the inversve of @enable for atomic drivers.
+ *
+ * NOTE:
+ *
+ * With legacy CRTC helpers there's a big semantic difference between
+ * @disable other hooks (like @prepare or @dpms) used to shut down a
+ * CRTC: @disable is only called when also logically disabling the
+ * display pipeline and needs to release any resources acquired in
+ * @mode_set (like shared PLLs, or again release pinned framebuffers).
+ *
+ * Therefore @disable must be the inverse of @mode_set plus @commit for
+ * drivers still using legacy CRTC helpers, which is different from the
+ * rules under atomic.
+ */
void (*disable)(struct drm_crtc *crtc);
+
+ /**
+ * @enable:
+ *
+ * This callback should be used to enable the CRTC. With the atomic
+ * drivers it is called before all encoders connected to this CRTC are
+ * enabled through the encoder's own ->enable hook. If that sequence is
+ * too simple drivers can just add their own hooks and call it from this
+ * CRTC callback here by looping over all encoders connected to it using
+ * for_each_encoder_on_crtc().
+ *
+ * This hook is used only by atomic helpers, for symmetry with @disable.
+ * Atomic drivers don't need to implement it if there's no need to
+ * enable anything at the CRTC level. To ensure that runtime PM handling
+ * (using either DPMS or the new "ACTIVE" property) works
+ * @enable must be the inversve of @disable for atomic drivers.
+ */
void (*enable)(struct drm_crtc *crtc);

/**
@@ -206,46 +384,221 @@ static inline void drm_crtc_helper_add(struct drm_crtc *crtc,

/**
* struct drm_encoder_helper_funcs - helper operations for encoders
- * @dpms: set power state
- * @mode_fixup: try to fixup proposed mode for this connector
- * @prepare: part of the disable sequence, called before the CRTC modeset
- * @commit: called after the CRTC modeset
- * @mode_set: set this mode, optional for atomic helpers
- * @get_crtc: return CRTC that the encoder is currently attached to
- * @detect: connection status detection
- * @disable: disable encoder when not in use (overrides DPMS off)
- * @enable: enable encoder
- * @atomic_check: check for validity of an atomic update
- *
- * The helper operations are called by the mid-layer CRTC helper.
*
- * Note that with atomic helpers @dpms, @prepare and @commit hooks are
- * deprecated. Used @enable and @disable instead exclusively.
- *
- * With legacy crtc helpers there's a big semantic difference between @disable
- * and the other hooks: @disable also needs to release any resources acquired in
- * @mode_set (like shared PLLs).
+ * These hooks are used by the legacy CRTC helpers, the transitional plane
+ * helpers and the new atomic modesetting helpers.
*/
struct drm_encoder_helper_funcs {
+ /**
+ * @dpms:
+ *
+ * Callback to control power levels on the encoder. If the mode passed in
+ * is unsupported, the provider must use the next lowest power level.
+ * This is used by the legacy encoder helpers to implement DPMS
+ * functionality in drm_helper_connector_dpms().
+ *
+ * This callback is also used to disable a encoder by calling it with
+ * DRM_MODE_DPMS_OFF if the @disable hook isn't used.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for enabling and disabling a encoder to
+ * facilitate transitions to atomic, but it is deprecated. Instead
+ * @enable and @disable should be used.
+ */
void (*dpms)(struct drm_encoder *encoder, int mode);

+ /**
+ * @mode_fixup:
+ *
+ * This callback is used to validate and adjust a mode. The paramater
+ * mode is the display mode that should be fed to the next element in
+ * the display chain, either the final &drm_connector or a &drm_bridge.
+ * The parameter adjusted_mode is the input mode the encoder requires. It
+ * can be modified by this callback and does not need to match mode.
+ *
+ * This function is used by both legacy CRTC helpers and atomic helpers.
+ * With atomic helpers it is optional.
+ *
+ * NOTE:
+ *
+ * This function is called in the check phase of atomic modesets, which
+ * can be aborted for any reason (including on userspace's request to
+ * just check whether a configuration would be possible). Atomic drivers
+ * MUST NOT touch any persistent state (hardware or software) or data
+ * structures except the passed in adjusted_mode parameter.
+ *
+ * This is in contrast to the legacy CRTC helpers where this was
+ * allowed.
+ *
+ * Atomic drivers which need to inspect and adjust more state should
+ * instead use the @atomic_check callback.
+ *
+ * RETURNS:
+ *
+ * True if an acceptable configuration is possible, false if the modeset
+ * operation should be rejected.
+ */
bool (*mode_fixup)(struct drm_encoder *encoder,
const struct drm_display_mode *mode,
struct drm_display_mode *adjusted_mode);
+
+ /**
+ * @prepare:
+ *
+ * This callback should prepare the encoder for a subsequent modeset,
+ * which in practice means the driver should disable the encoder if it
+ * is running. Most drivers ended up implementing this by calling their
+ * @dpms hook with DRM_MODE_DPMS_OFF.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for disabling a encoder to facilitate
+ * transitions to atomic, but it is deprecated. Instead @disable should
+ * be used.
+ */
void (*prepare)(struct drm_encoder *encoder);
+
+ /**
+ * @commit:
+ *
+ * This callback should commit the new mode on the encoder after a modeset,
+ * which in practice means the driver should enable the encoder. Most
+ * drivers ended up implementing this by calling their @dpms hook with
+ * DRM_MODE_DPMS_ON.
+ *
+ * This callback is used by the legacy CRTC helpers. Atomic helpers
+ * also support using this hook for enabling a encoder to facilitate
+ * transitions to atomic, but it is deprecated. Instead @enable should
+ * be used.
+ */
void (*commit)(struct drm_encoder *encoder);
+
+ /**
+ * @mode_set:
+ *
+ * This callback is used to update the display mode of an encoder.
+ *
+ * Note that the display pipe is completely off when this function is
+ * called. Drivers which need hardware to be running before they program
+ * the new display mode (because they implement runtime PM) should not
+ * use this hook, because the helper library calls it only once and not
+ * every time the display pipeline is suspend using either DPMS or the
+ * new "ACTIVE" property. Such drivers should instead move all their
+ * encoder setup into the ->enable() callback.
+ *
+ * This callback is used both by the legacy CRTC helpers and the atomic
+ * modeset helpers. It is optional in the atomic helpers.
+ */
void (*mode_set)(struct drm_encoder *encoder,
struct drm_display_mode *mode,
struct drm_display_mode *adjusted_mode);
+
+ /**
+ * @get_crtc:
+ *
+ * This callback is used by the legacy CRTC helpers to work around
+ * deficiencies in its own book-keeping.
+ *
+ * Do not use, use atomic helpers instead, which get the book keeping
+ * right.
+ *
+ * FIXME:
+ *
+ * Currently only nouveau is using this, and as soon as nouveau is
+ * atomic we can ditch this hook.
+ */
struct drm_crtc *(*get_crtc)(struct drm_encoder *encoder);
- /* detect for DAC style encoders */
+
+ /**
+ * @detect:
+ *
+ * This callback can be used by drivers who want to do detection on the
+ * encoder object instead of in connector functions.
+ *
+ * It is not used by any helper and therefore has purely driver-specific
+ * semantics. New drivers shouldn't use this and instead just implement
+ * their own private callbacks.
+ *
+ * FIXME:
+ *
+ * This should just be converted into a pile of driver vfuncs.
+ * Currently radeon, amdgpu and nouveau are using it.
+ */
enum drm_connector_status (*detect)(struct drm_encoder *encoder,
struct drm_connector *connector);
+
+ /**
+ * @disable:
+ *
+ * This callback should be used to disable the encoder. With the atomic
+ * drivers it is called before this encoder's CRTC has been shut off
+ * using the CRTC's own ->disable hook. If that sequence is too simple
+ * drivers can just add their own driver private encoder hooks and call
+ * them from CRTC's callback by looping over all encoders connected to
+ * it using for_each_encoder_on_crtc().
+ *
+ * This hook is used both by legacy CRTC helpers and atomic helpers.
+ * Atomic drivers don't need to implement it if there's no need to
+ * disable anything at the encoder level. To ensure that runtime PM
+ * handling (using either DPMS or the new "ACTIVE" property) works
+ * @disable must be the inversve of @enable for atomic drivers.
+ *
+ * NOTE:
+ *
+ * With legacy CRTC helpers there's a big semantic difference between
+ * @disable other hooks (like @prepare or @dpms) used to shut down a
+ * encoder: @disable is only called when also logically disabling the
+ * display pipeline and needs to release any resources acquired in
+ * @mode_set (like shared PLLs, or again release pinned framebuffers).
+ *
+ * Therefore @disable must be the inverse of @mode_set plus @commit for
+ * drivers still using legacy CRTC helpers, which is different from the
+ * rules under atomic.
+ */
void (*disable)(struct drm_encoder *encoder);

+ /**
+ * @enable:
+ *
+ * This callback should be used to enable the encoder. With the atomic
+ * drivers it is called after this encoder's CRTC has been enabled using
+ * the CRTC's own ->enable hook. If that sequence is too simple drivers
+ * can just add their own driver private encoder hooks and call them
+ * from CRTC's callback by looping over all encoders connected to it
+ * using for_each_encoder_on_crtc().
+ *
+ * This hook is used only by atomic helpers, for symmetry with @disable.
+ * Atomic drivers don't need to implement it if there's no need to
+ * enable anything at the encoder level. To ensure that runtime PM handling
+ * (using either DPMS or the new "ACTIVE" property) works
+ * @enable must be the inversve of @disable for atomic drivers.
+ */
void (*enable)(struct drm_encoder *encoder);

- /* atomic helpers */
+ /**
+ * @atomic_check:
+ *
+ * This callback is used to validate encoder state for atomic drivers.
+ * Since the encoder is the object connecting the CRTC and connector it
+ * gets passed both states, to be able to validate interactions and
+ * update the CRTC to match what the encoder needs for the requested
+ * connector.
+ *
+ * This function is used by the atomic helpers, but it is optional.
+ *
+ * NOTE:
+ *
+ * This function is called in the check phase of an atomic update. The
+ * driver is not allowed to change anything outside of the free-standing
+ * state objects passed-in or assembled in the overall &drm_atomic_state
+ * update tracking structure.
+ *
+ * RETURNS:
+ *
+ * 0 on success, -EINVAL if the state or the transition can't be
+ * support, -ENOMEM on memory allocation failure and -EDEADLK if an
+ * attempt to obtain another state object ran into a &drm_modeset_lock
+ * deadlock.
+ */
int (*atomic_check)(struct drm_encoder *encoder,
struct drm_crtc_state *crtc_state,
struct drm_connector_state *conn_state);
--
2.5.1