'\" t
.\"     Title: drm_vblank_pre_modeset
.\"    Author: 
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: May 2018
.\"    Manual: DRM Core
.\"    Source: Kernel Hackers Manual 3.16.56
.\"  Language: English
.\"
.TH "DRM_VBLANK_PRE_MODES" "9" "May 2018" "Kernel Hackers Manual 3\&.16\&" "DRM Core"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
drm_vblank_pre_modeset \- account for vblanks across mode sets
.SH "SYNOPSIS"
.HP \w'void\ drm_vblank_pre_modeset('u
.BI "void drm_vblank_pre_modeset(struct\ drm_device\ *\ " "dev" ", int\ " "crtc" ");"
.SH "ARGUMENTS"
.PP
\fIdev\fR
.RS 4
DRM device
.RE
.PP
\fIcrtc\fR
.RS 4
CRTC in question
.RE
.SH "DESCRIPTION"
.PP
Account for vblank events across mode setting events, which will likely reset the hardware frame counter\&.
.PP
This is done by grabbing a temporary vblank reference to ensure that the vblank interrupt keeps running across the modeset sequence\&. With this the software\-side vblank frame counting will ensure that there are no jumps or discontinuities\&.
.PP
Unfortunately this approach is racy and also doesn\*(Aqt work when the vblank interrupt stops running, e\&.g\&. across system suspend resume\&. It is therefore highly recommended that drivers use the newer
\fBdrm_vblank_off\fR
and
\fBdrm_vblank_on\fR
instead\&.
\fBdrm_vblank_pre_modeset\fR
only works correctly when using
\(lqcooked\(rq
software vblank frame counters and not relying on any hardware counters\&.
.PP
Drivers must call
\fBdrm_vblank_post_modeset\fR
when re\-enabling the same crtc again\&.
.SH "AUTHORS"
.PP
\fBJesse Barnes\fR <\&jesse.barnes@intel.com\&>
.br
Intel Corporation, 
	    
	  
.RS 4
Initial version
.RE
.PP
\fBLaurent Pinchart\fR <\&laurent.pinchart@ideasonboard.com\&>
.br
Ideas on board SPRL, 
	    
	  
.RS 4
Driver internals
.RE
.PP
\fBDaniel Vetter\fR <\&daniel.vetter@ffwll.ch\&>
.br
Intel Corporation, 
	    
	  
.RS 4
Contributions all over the place
.RE
.SH "COPYRIGHT"
.br