X-Servers before 1.12.0 don't have the DRI2SwapLimit()
API. On these, default to a swaplimit of 1 - double-buffering.
This patch implements support for swap limit of 2,
triple-buffering, on old x-servers via Francisco Jerez
previous hack:
Return DRI2SwapComplete() before the swap has completed,
so clients don't get blocked on the pending swap. This
allows for a "triple-buffering look-alike" behaviour, but
breaks the swap scheduling and timestamping defined
in the OML_sync_control spec, so applications which
rely on conformant behaviour will break with a swap
limit of 2 on pre 1.12.0 x-servers.
Signed-off-by: Mario Kleiner <mario.klei...@tuebingen.mpg.de>
---
man/nouveau.man | 6 +++++-
src/nouveau_dri2.c | 32 +++++++++++++++++++++++++++++---
src/nv_driver.c | 11 ++++++-----
3 files changed, 40 insertions(+), 9 deletions(-)
diff --git a/man/nouveau.man b/man/nouveau.man
index 59f6c1a..7c72907 100644
--- a/man/nouveau.man
+++ b/man/nouveau.man
@@ -101,7 +101,11 @@ a drawable before a client is blocked.
A value of 1 corresponds to double-buffering. A value of 2 corresponds
to triple-buffering. Higher values may allow higher framerate, but also
increase lag for interactive applications, e.g., games. Nouveau currently
-supports a maximum value of 2 on XOrg 1.12+ and a maximum of 1 on older
servers.
+reliably supports a maximum value of 2 on XOrg 1.12+. A maximum setting of 2
+on older x-servers is allowed, but it will break conformance with the
+OpenML OML_sync_control specification and will cause failure of software
+that relies on correct presentation timing behaviour as defined in that
+specification.
.br
Default: 2 for XOrg 1.12+, 1 for older servers.
.SH "SEE ALSO"
diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
index fdc5148..f0c7fec 100644
--- a/src/nouveau_dri2.c
+++ b/src/nouveau_dri2.c
@@ -255,6 +255,18 @@ nouveau_dri2_swap_limit_validate(DrawablePtr draw, int
swap_limit)
}
#endif
+/* Shall we intentionally violate the OML_sync_control spec to
+ * get some sort of triple-buffering behaviour on a pre 1.12.0
+ * x-server?
+ */
+static Bool violate_oml(DrawablePtr draw)
+{
+ ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
+ NVPtr pNv = NVPTR(scrn);
+
+ return (DRI2INFOREC_VERSION < 6) && (pNv->swap_limit > 1);
+}
+
static void
nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
unsigned int tv_sec, unsigned int tv_usec,
@@ -319,7 +331,9 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int
frame,
if (DRI2CanFlip(draw)) {
type = DRI2_FLIP_COMPLETE;
- ret = drmmode_page_flip(draw, src_pix, s,
ref_crtc_hw_id);
+ ret = drmmode_page_flip(draw, src_pix,
+ violate_oml(draw) ? NULL : s,
+ ref_crtc_hw_id);
if (!ret)
goto out;
}
@@ -330,7 +344,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int
frame,
DamageRegionProcessPending(draw);
/* If it is a page flip, finish it in the flip event handler. */
- if (type == DRI2_FLIP_COMPLETE)
+ if ((type == DRI2_FLIP_COMPLETE) && !violate_oml(draw))
return;
} else {
type = DRI2_BLIT_COMPLETE;
@@ -344,7 +358,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int
frame,
REGION_TRANSLATE(0, ®, -draw->x, -draw->y);
nouveau_dri2_copy_region(draw, ®, s->dst, s->src);
- if (can_sync_to_vblank(draw)) {
+ if (can_sync_to_vblank(draw) && !violate_oml(draw)) {
/* Request a vblank event one vblank from now, the most
* likely (optimistic?) time a direct framebuffer blit
* will complete or a desktop compositor will update its
@@ -361,6 +375,14 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int
frame,
}
}
+ /* Special triple-buffering hack for old pre 1.12.0 x-servers used? */
+ if (violate_oml(draw)) {
+ /* Signal to client that swap completion timestamps and counts
+ * are invalid - they violate the specification.
+ */
+ frame = tv_sec = tv_usec = 0;
+ }
+
/*
* Tell the X server buffers are already swapped even if they're
* not, to prevent it from blocking the client on the next
@@ -371,6 +393,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int
frame,
* It is still needed as a fallback for some copy swaps as
* we lack a method to detect true swap completion for
* DRI2_BLIT_COMPLETE.
+ *
+ * It is also used if triple-buffering is requested on
+ * old x-servers which don't support the DRI2SwapLimit()
+ * function.
*/
DRI2SwapComplete(s->client, draw, frame, tv_sec, tv_usec,
type, s->func, s->data);
diff --git a/src/nv_driver.c b/src/nv_driver.c
index 5def531..7512464 100644
--- a/src/nv_driver.c
+++ b/src/nv_driver.c
@@ -863,11 +863,12 @@ NVPreInit(ScrnInfoPtr pScrn, int flags)
reason = "";
from = X_CONFIG;
- if (DRI2INFOREC_VERSION < 6) {
- /* No swap limit api in server. Stick to server default
of 1. */
- pNv->swap_limit = 1;
- from = X_DEFAULT;
- reason = ": This X-Server only supports a swap limit of
1.";
+ if ((DRI2INFOREC_VERSION < 6) && (pNv->swap_limit > 1)) {
+ /* No swap limit api in server. A value > 1 requires use
+ * of problematic hacks.
+ */
+ from = X_WARNING;
+ reason = ": Caution: Use of this swap limit > 1
violates OML_sync_control spec on this X-Server!\n";
}
} else {
/* Driver default: Double buffering on old servers,
triple-buffering
--
1.7.5.4
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