intel: Make the option to control VSync and PageFlip explict

Too often our implementation of vsync or pageflip is buggy, or for some
other reason it is desired by the user to disable those code paths. Make
it possible once again by restoring the Options for the user to control.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

man/intel.man

@@ -196,13 +196,31 @@ i.e. perform synchronous rendering.
 Default: Disabled
 .TP
 .TP
+.BI "Option \*qVSync\*q \*q" boolean \*q
+This option controls the use of commands to synchronise rendering with the
+vertical refresh of the display. Some rendering commands have the option
+to be performed in a "tear-free" fashion by stalling the GPU to wait for
+the display to be outside of the region to be updated. This slows down all
+rendering, and historically has been the source of many GPU hangs.
+.IP
+Default: enabled.
+.TP
+.BI "Option \*qPageFlip\*q \*q" boolean \*q
+This option controls the use of commands to flip the scanout address on a
+VBlank. This is used by glXSwapBuffers to efficiently perform the back-to-front
+exchange at the end of a frame without incurring the penalty of a copy, or
+stalling the render pipeline (the flip is performed asynchronrously to the
+render command stream by the display engine). However, it has historically
+been the source of many GPU hangs.
+.IP
+Default: enabled.
+.TP
 .BI "Option \*qSwapbuffersWait\*q \*q" boolean \*q
 This option controls the behavior of glXSwapBuffers and glXCopySubBufferMESA
 calls by GL applications.  If enabled, the calls will avoid tearing by making
 sure the display scanline is outside of the area to be copied before the copy
 occurs.  If disabled, no scanline synchronization is performed, meaning tearing
-will likely occur.  Note that when enabled, this option can adversely affect
-the framerate of applications that render frames at less than refresh rate.
+will likely occur.
 .IP
 Default: enabled.
 .TP

src/intel_options.c

@@ -13,6 +13,8 @@ const OptionInfoRec intel_options[] = {
 	{OPTION_VIDEO_KEY,	"VideoKey",	OPTV_INTEGER,	{0},	0},
 	{OPTION_TILING_2D,	"Tiling",	OPTV_BOOLEAN,	{0},	1},
 	{OPTION_TILING_FB,	"LinearFramebuffer",	OPTV_BOOLEAN,	{0},	0},
+	{OPTION_VSYNC, "VSync", OPTV_BOOLEAN,	{0},	1},
+	{OPTION_PAGEFLIP, "PageFlip", OPTV_BOOLEAN,	{0},	1},
 	{OPTION_SWAPBUFFERS_WAIT, "SwapbuffersWait", OPTV_BOOLEAN,	{0},	1},
 	{OPTION_TRIPLE_BUFFER,	"TripleBuffer", OPTV_BOOLEAN,	{0},	1},
 	{OPTION_PREFER_OVERLAY, "XvPreferOverlay", OPTV_BOOLEAN, {0}, 0},

src/intel_options.h

@@ -19,6 +19,8 @@ enum intel_options {
 	OPTION_COLOR_KEY,
 	OPTION_TILING_2D,
 	OPTION_TILING_FB,
+	OPTION_VSYNC,
+	OPTION_PAGEFLIP,
 	OPTION_SWAPBUFFERS_WAIT,
 	OPTION_TRIPLE_BUFFER,
 	OPTION_PREFER_OVERLAY,

src/sna/sna.h

@@ -226,7 +226,8 @@ struct sna {
 	unsigned flags;
 #define SNA_NO_WAIT		0x1
 #define SNA_NO_FLIP		0x2
-#define SNA_TRIPLE_BUFFER	0x4
+#define SNA_NO_VSYNC		0x4
+#define SNA_TRIPLE_BUFFER	0x8
 #define SNA_TEAR_FREE		0x10
 #define SNA_FORCE_SHADOW	0x20
 #define SNA_FLUSH_GTT		0x40

src/sna/sna_display.c

@@ -3627,6 +3627,9 @@ sna_wait_for_scanline(struct sna *sna,
 	assert(to_sna_crtc(crtc)->bo != NULL);
 	assert(pixmap == sna->front);
 
+	if (sna->flags & SNA_NO_VSYNC)
+		return false;
+
 	/*
 	 * Make sure we don't wait for a scanline that will
 	 * never occur

src/sna/sna_dri.c

@@ -303,7 +303,7 @@ sna_dri_create_buffer(DrawablePtr draw,
 	case DRI2BufferBackLeft:
 		if (draw->width  == sna->front->drawable.width &&
 		    draw->height == sna->front->drawable.height &&
-		    (sna->flags & SNA_NO_FLIP) == 0)
+		    (sna->flags & (SNA_NO_WAIT | SNA_NO_FLIP)) == 0)
 			flags |= CREATE_SCANOUT;
 	case DRI2BufferBackRight:
 	case DRI2BufferFrontRight:
@@ -1080,6 +1080,8 @@ can_flip(struct sna * sna,
 	WindowPtr win = (WindowPtr)draw;
 	PixmapPtr pixmap;
 
+	assert((sna->flags & SNA_NO_WAIT) == 0);
+
 	if (draw->type == DRAWABLE_PIXMAP)
 		return false;
 
@@ -1967,7 +1969,9 @@ sna_dri_schedule_swap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
 	assert(sna_pixmap_from_drawable(draw)->flush);
 
 	/* Drawable not displayed... just complete the swap */
-	pipe = sna_dri_get_pipe(draw);
+	pipe = -1;
+	if (sna->flags & SNA_NO_WAIT)
+		pipe = sna_dri_get_pipe(draw);
 	if (pipe == -1) {
 		DBG(("%s: off-screen, immediate update\n", __FUNCTION__));
 		goto blit;

src/sna/sna_driver.c

@@ -294,12 +294,20 @@ static void sna_selftest(void)
 	sna_damage_selftest();
 }
 
+static bool has_vsync(struct sna *sna)
+{
+	if (sna->flags & SNA_IS_HOSTED)
+		return false;
+
+	return true;
+}
+
 static bool has_pageflipping(struct sna *sna)
 {
 	drm_i915_getparam_t gp;
 	int v;
 
-	if (sna->flags & (SNA_IS_HOSTED | SNA_NO_WAIT))
+	if (sna->flags & SNA_IS_HOSTED)
 		return false;
 
 	v = 0;
@@ -508,13 +516,23 @@ static Bool sna_pre_init(ScrnInfoPtr scrn, int flags)
 
 	if (!xf86ReturnOptValBool(sna->Options, OPTION_SWAPBUFFERS_WAIT, TRUE))
 		sna->flags |= SNA_NO_WAIT;
-	if (xf86ReturnOptValBool(sna->Options, OPTION_TRIPLE_BUFFER, TRUE))
-		sna->flags |= SNA_TRIPLE_BUFFER;
-	if (has_pageflipping(sna)) {
-		if (xf86ReturnOptValBool(sna->Options, OPTION_TEAR_FREE, FALSE))
-			sna->flags |= SNA_TEAR_FREE;
-	} else
+
+	if (!has_vsync(sna) ||
+	    !xf86ReturnOptValBool(sna->Options, OPTION_VSYNC, TRUE))
+		sna->flags |= SNA_NO_VSYNC;
+
+	if (!has_pageflipping(sna) ||
+	    !xf86ReturnOptValBool(sna->Options, OPTION_PAGEFLIP, TRUE))
 		sna->flags |= SNA_NO_FLIP;
+
+	if ((sna->flags & (SNA_NO_VSYNC | SNA_NO_FLIP | SNA_NO_WAIT)) == 0 &&
+	    xf86ReturnOptValBool(sna->Options, OPTION_TRIPLE_BUFFER, TRUE))
+		sna->flags |= SNA_TRIPLE_BUFFER;
+
+	if ((sna->flags & (SNA_NO_VSYNC | SNA_NO_FLIP)) == 0 &&
+	    xf86ReturnOptValBool(sna->Options, OPTION_TEAR_FREE, FALSE))
+		sna->flags |= SNA_TEAR_FREE;
+
 	if (xf86ReturnOptValBool(sna->Options, OPTION_CRTC_PIXMAPS, FALSE))
 		sna->flags |= SNA_FORCE_SHADOW;