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compositor-drm: Add comment for newly added drm_waitvblank_pipe()

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Bryce Harrington 2015-06-30 13:25:46 -07:00
parent 2ab4f4e384
commit ada4f07bbb
1 changed files with 13 additions and 0 deletions
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13
src/compositor-drm.c
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@ -597,6 +597,19 @@ drm_output_set_gamma(struct weston_output *output_base,
weston_log("set gamma failed: %m\n");
}
/* Determine the type of vblank synchronization to use for the output.
*
* The pipe parameter indicates which CRTC is in use. Knowing this, we
* can determine which vblank sequence type to use for it. Traditional
* cards had only two CRTCs, with CRTC 0 using no special flags, and
* CRTC 1 using DRM_VBLANK_SECONDARY. The first bit of the pipe
* parameter indicates this.
*
* Bits 1-5 of the pipe parameter are 5 bit wide pipe number between
* 0-31. If this is non-zero it indicates we're dealing with a
* multi-gpu situation and we need to calculate the vblank sync
* using DRM_BLANK_HIGH_CRTC_MASK.
*/
static unsigned int drm_waitvblank_pipe(struct drm_output *output)
{
if (output->pipe > 1)