[PATCH xserver] xf86-video-modesetting: Fix ms_queue_vblank(flags = MS_QUEUE_RELATIVE)

[Alex Goins]

Adding Keith, as this is a regression that completely breaks PRIME Sync configs
at top of tree.

Thanks,
Alex

On Fri, 20 Oct 2017, Alex Goins wrote:

> Change 677c32bc refactored all usages of drmWaitVBlank() into a helper function,
> ms_queue_vblank().
> 
> ms_queue_vblank() takes in an MS_QUEUE_RELATIVE flag to indicate that the
> sequence number is relative rather than absolute, but still treats the actual
> sequence number as absolute, passing it through ms_crtc_msc_to_kernel_msc()
> unconditionally before calling drmWaitVBlank().
> 
> ms_crtc_msc_to_kernel_msc() works by subtracting a vblank offset from the
> provided sequence number, which only makes sense for absolute sequence numbers.
> In the case of PRIME Sync, drmmode_SharedPixmapPrsentOnVBlank() passes in 1,
> which results in a large negative vblank offset. After subtracting, we're left
> with a relative sequence number of 100,000+, i.e. wait for 100,000+ vblanks...
> 
> In the relative case we want to pass in the sequence number unmodified. Simply
> add a check to do this.
> 
> Signed-off-by: Alex Goins <agoins at nvidia.com>
> ---
>  hw/xfree86/drivers/modesetting/vblank.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/xfree86/drivers/modesetting/vblank.c b/hw/xfree86/drivers/modesetting/vblank.c
> index 31cf0bd..fe046e4 100644
> --- a/hw/xfree86/drivers/modesetting/vblank.c
> +++ b/hw/xfree86/drivers/modesetting/vblank.c
> @@ -219,7 +219,8 @@ ms_queue_vblank(xf86CrtcPtr crtc, ms_queue_flag flags,
>          if (flags & MS_QUEUE_NEXT_ON_MISS)
>              vbl.request.type |= DRM_VBLANK_NEXTONMISS;
>  
> -        vbl.request.sequence = ms_crtc_msc_to_kernel_msc(crtc, msc);
> +        vbl.request.sequence = (flags & MS_QUEUE_RELATIVE) ?
> +                                    msc : ms_crtc_msc_to_kernel_msc(crtc, msc);
>          vbl.request.signal = seq;
>          ret = drmWaitVBlank(ms->fd, &vbl);
>          if (ret == 0) {
> -- 
> 2.7.4
> 
> 

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