drm_calc_vbltimestamp_from_scanoutpos: Precise vblank timestamp helper

SYNOPSIS

int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device * dev, int crtc, int * max_error, struct timeval * vblank_time, unsigned flags, const struct drm_crtc * refcrtc, const struct drm_display_mode * mode);

ARGUMENTS

dev

DRM device

crtc

Which CRTC's vblank timestamp to retrieve

max_error

Desired maximum allowable error in timestamps (nanosecs) On return contains true maximum error of timestamp

vblank_time

Pointer to struct timeval which should receive the timestamp

flags

Flags to pass to driver: 0 = Default, DRM_CALLED_FROM_VBLIRQ = If function is called from vbl IRQ handler

refcrtc

CRTC which defines scanout timing

mode

mode which defines the scanout timings

DESCRIPTION

Implements calculation of exact vblank timestamps from given drm_display_mode timings and current video scanout position of a CRTC. This can be called from within get_vblank_timestamp implementation of a kms driver to implement the actual timestamping.

Should return timestamps conforming to the OML_sync_control OpenML extension specification. The timestamp corresponds to the end of the vblank interval, aka start of scanout of topmost-leftmost display pixel in the following video frame.

Requires support for optional dev->driver->get_scanout_position in kms driver, plus a bit of setup code to provide a drm_display_mode that corresponds to the true scanout timing.

The current implementation only handles standard video modes. It returns as no operation if a doublescan or interlaced video mode is active. Higher level code is expected to handle this.

RETURNS

Negative value on error, failure or if not supported in current

VIDEO MODE

-EINVAL - Invalid CRTC. -EAGAIN - Temporary unavailable, e.g., called before initial modeset. -ENOTSUPP - Function not supported in current display mode. -EIO - Failed, e.g., due to failed scanout position query.

Returns or'ed positive status flags on success:

DRM_VBLANKTIME_SCANOUTPOS_METHOD - Signal this method used for timestamping. DRM_VBLANKTIME_INVBL - Timestamp taken while scanout was in vblank interval.

AUTHORS

Jesse Barnes <[email protected]>

Intel Corporation,

Initial version

Laurent Pinchart <[email protected]>

Ideas on board SPRL,

Driver internals

Daniel Vetter <[email protected]>