SYNOPSIS

struct drm_encoder_helper_funcs {
void (* dpms) (struct drm_encoder *encoder, int mode);
bool (* mode_fixup) (struct drm_encoder *encoder,const struct drm_display_mode *mode,struct drm_display_mode *adjusted_mode);
void (* prepare) (struct drm_encoder *encoder);
void (* commit) (struct drm_encoder *encoder);
void (* mode_set) (struct drm_encoder *encoder,struct drm_display_mode *mode,struct drm_display_mode *adjusted_mode);
struct drm_crtc *(* get_crtc) (struct drm_encoder *encoder);
enum drm_connector_status (* detect) (struct drm_encoder *encoder,struct drm_connector *connector);
void (* disable) (struct drm_encoder *encoder);
void (* enable) (struct drm_encoder *encoder);
int (* atomic_check) (struct drm_encoder *encoder,struct drm_crtc_state *crtc_state,struct drm_connector_state *conn_state);
};

MEMBERS

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 an 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 an encoder to facilitate transitions to atomic, but it is deprecated. Instead enable and disable should be used.

mode_fixup

This callback is used to validate and adjust a mode. The parameter 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. This hook 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.

Also beware that neither core nor helpers filter modes before passing them to the driver: While the list of modes that is advertised to userspace is filtered using the connector's ->mode_valid callback, neither the core nor the helpers do any filtering on modes passed in from userspace when setting a mode. It is therefore possible for userspace to pass in a mode that was previously filtered out using ->mode_valid or add a custom mode that wasn't probed from EDID or similar to begin with. Even though this is an advanced feature and rarely used nowadays, some users rely on being able to specify modes manually so drivers must be prepared to deal with it. Specifically this means that all drivers need not only validate modes in ->mode_valid but also in ->mode_fixup to make sure invalid modes passed in from userspace are rejected.

RETURNS:

True if an acceptable configuration is possible, false if the modeset operation should be rejected.

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 an encoder to facilitate transitions to atomic, but it is deprecated. Instead disable should be used.

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 an encoder to facilitate transitions to atomic, but it is deprecated. Instead enable should be used.

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.

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.

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.

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 inverse of enable for atomic drivers.

NOTE:

With legacy CRTC helpers there's a big semantic difference between disable and 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.

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 inverse of disable for atomic drivers.

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 supported, -ENOMEM on memory allocation failure and -EDEADLK if an attempt to obtain another state object ran into a drm_modeset_lock deadlock.

DESCRIPTION

These hooks are used by the legacy CRTC helpers, the transitional plane helpers and the new atomic modesetting helpers.

AUTHORS

Jesse Barnes <[email protected]>
Intel Corporation,         
        

Initial version

Laurent Pinchart <[email protected]>
Ideas on board SPRL,         
        

Driver internals

Daniel Vetter <[email protected]>
Intel Corporation,         
        

Contributions all over the place

Lukas Wunner <[email protected]>

vga_switcheroo documentation

COPYRIGHT