drm/i915: FIFO watermark calculation fixes

I discovered several bugs in the FIFO code that was recently applied.
Some of them fell into the "how did this ever work" category, since in
some cases we were using the wrong FIFO size values, and the
calculations ended up being way off.

This patch fixes all the bugs I found, and works well on my GM45, 915GM
and 855GM test machines; but as usual with these sorts of patches
broader testing is definitely requested (in particular this patch
affects 830, 845 and 865 for which I don't have test hardware).

Overall, the patch clarifies the watermark calculation function by
adding some comments and debug info, and making the variable names a
bit clearer.  The "get FIFO size" portion of the code has also been
corrected, so we should be able to properly detect the FIFO allocations
for each pipe, for use in the watermark calculation.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -1618,7 +1618,7 @@
 #define I830_FIFO_LINE_SIZE	32
 #define I945_FIFO_SIZE		127 /* 945 & 965 */
 #define I915_FIFO_SIZE		95
-#define I855GM_FIFO_SIZE	255
+#define I855GM_FIFO_SIZE	127 /* In cachelines */
 #define I830_FIFO_SIZE		95
 #define I915_MAX_WM		0x3f
 

drivers/gpu/drm/i915/intel_display.c

@@ -1623,44 +1623,67 @@ static struct intel_watermark_params igd_cursor_hplloff_wm = {
 	IGD_FIFO_LINE_SIZE
 };
 static struct intel_watermark_params i945_wm_info = {
-	I915_FIFO_LINE_SIZE,
+	I945_FIFO_SIZE,
 	I915_MAX_WM,
 	1,
-	0,
-	IGD_FIFO_LINE_SIZE
+	2,
+	I915_FIFO_LINE_SIZE
 };
 static struct intel_watermark_params i915_wm_info = {
-	I945_FIFO_SIZE,
+	I915_FIFO_SIZE,
 	I915_MAX_WM,
 	1,
-	0,
+	2,
 	I915_FIFO_LINE_SIZE
 };
 static struct intel_watermark_params i855_wm_info = {
 	I855GM_FIFO_SIZE,
 	I915_MAX_WM,
 	1,
-	0,
+	2,
 	I830_FIFO_LINE_SIZE
 };
 static struct intel_watermark_params i830_wm_info = {
 	I830_FIFO_SIZE,
 	I915_MAX_WM,
 	1,
-	0,
+	2,
 	I830_FIFO_LINE_SIZE
 };
 
+/**
+ * intel_calculate_wm - calculate watermark level
+ * @clock_in_khz: pixel clock
+ * @wm: chip FIFO params
+ * @pixel_size: display pixel size
+ * @latency_ns: memory latency for the platform
+ *
+ * Calculate the watermark level (the level at which the display plane will
+ * start fetching from memory again).  Each chip has a different display
+ * FIFO size and allocation, so the caller needs to figure that out and pass
+ * in the correct intel_watermark_params structure.
+ *
+ * As the pixel clock runs, the FIFO will be drained at a rate that depends
+ * on the pixel size.  When it reaches the watermark level, it'll start
+ * fetching FIFO line sized based chunks from memory until the FIFO fills
+ * past the watermark point.  If the FIFO drains completely, a FIFO underrun
+ * will occur, and a display engine hang could result.
+ */
 static unsigned long intel_calculate_wm(unsigned long clock_in_khz,
 					struct intel_watermark_params *wm,
 					int pixel_size,
 					unsigned long latency_ns)
 {
-	unsigned long bytes_required, wm_size;
+	unsigned long entries_required, wm_size;
+
+	entries_required = (clock_in_khz * pixel_size * latency_ns) / 1000000;
+	entries_required /= wm->cacheline_size;
+
+	DRM_DEBUG("FIFO entries required for mode: %d\n", entries_required);
 
-	bytes_required = (clock_in_khz * pixel_size * latency_ns) / 1000000;
-	bytes_required /= wm->cacheline_size;
-	wm_size = wm->fifo_size - bytes_required - wm->guard_size;
+	wm_size = wm->fifo_size - (entries_required + wm->guard_size);
+
+	DRM_DEBUG("FIFO watermark level: %d\n", wm_size);
 
 	if (wm_size > wm->max_wm)
 		wm_size = wm->max_wm;
@@ -1799,8 +1822,37 @@ static void igd_enable_cxsr(struct drm_device *dev, unsigned long clock,
 	return;
 }
 
-const static int latency_ns = 5000; /* default for non-igd platforms */
+const static int latency_ns = 3000; /* default for non-igd platforms */
+
+static int intel_get_fifo_size(struct drm_device *dev, int plane)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	uint32_t dsparb = I915_READ(DSPARB);
+	int size;
+
+	if (IS_I9XX(dev)) {
+		if (plane == 0)
+			size = dsparb & 0x7f;
+		else
+			size = ((dsparb >> DSPARB_CSTART_SHIFT) & 0x7f) -
+				(dsparb & 0x7f);
+	} else if (IS_I85X(dev)) {
+		if (plane == 0)
+			size = dsparb & 0x1ff;
+		else
+			size = ((dsparb >> DSPARB_BEND_SHIFT) & 0x1ff) -
+				(dsparb & 0x1ff);
+		size >>= 1; /* Convert to cachelines */
+	} else {
+		size = dsparb & 0x7f;
+		size >>= 1; /* Convert to cachelines */
+	}
+
+	DRM_DEBUG("FIFO size - (0x%08x) %s: %d\n", dsparb, plane ? "B" : "A",
+		  size);
 
+	return size;
+}
 
 static void i965_update_wm(struct drm_device *dev)
 {
@@ -1817,101 +1869,87 @@ static void i9xx_update_wm(struct drm_device *dev, int planea_clock,
 			   int planeb_clock, int sr_hdisplay, int pixel_size)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	uint32_t fwater_lo = I915_READ(FW_BLC) & MM_FIFO_WATERMARK;
-	uint32_t fwater_hi = I915_READ(FW_BLC2) & LM_FIFO_WATERMARK;
-	int bsize, asize, cwm, bwm = 1, awm = 1, srwm = 1;
-	uint32_t dsparb = I915_READ(DSPARB);
-	int planea_entries, planeb_entries;
-	struct intel_watermark_params *wm_params;
+	uint32_t fwater_lo;
+	uint32_t fwater_hi;
+	int total_size, cacheline_size, cwm, srwm = 1;
+	int planea_wm, planeb_wm;
+	struct intel_watermark_params planea_params, planeb_params;
 	unsigned long line_time_us;
 	int sr_clock, sr_entries = 0;
 
+	/* Create copies of the base settings for each pipe */
 	if (IS_I965GM(dev) || IS_I945GM(dev))
-		wm_params = &i945_wm_info;
+		planea_params = planeb_params = i945_wm_info;
 	else if (IS_I9XX(dev))
-		wm_params = &i915_wm_info;
+		planea_params = planeb_params = i915_wm_info;
 	else
-		wm_params = &i855_wm_info;
-
-	planea_entries = intel_calculate_wm(planea_clock, wm_params,
-					    pixel_size, latency_ns);
-	planeb_entries = intel_calculate_wm(planeb_clock, wm_params,
-					    pixel_size, latency_ns);
+		planea_params = planeb_params = i855_wm_info;
 
-	DRM_DEBUG("FIFO entries - A: %d, B: %d\n", planea_entries,
-		  planeb_entries);
+	/* Grab a couple of global values before we overwrite them */
+	total_size = planea_params.fifo_size;
+	cacheline_size = planea_params.cacheline_size;
 
-	if (IS_I9XX(dev)) {
-		asize = dsparb & 0x7f;
-		bsize = (dsparb >> DSPARB_CSTART_SHIFT) & 0x7f;
-	} else {
-		asize = dsparb & 0x1ff;
-		bsize = (dsparb >> DSPARB_BEND_SHIFT) & 0x1ff;
-	}
-	DRM_DEBUG("FIFO size - A: %d, B: %d\n", asize, bsize);
+	/* Update per-plane FIFO sizes */
+	planea_params.fifo_size = intel_get_fifo_size(dev, 0);
+	planeb_params.fifo_size = intel_get_fifo_size(dev, 1);
 
-	/* Two extra entries for padding */
-	awm = asize - (planea_entries + 2);
-	bwm = bsize - (planeb_entries + 2);
-
-	/* Sanity check against potentially bad FIFO allocations */
-	if (awm <= 0) {
-		/* pipe is on but has too few FIFO entries */
-		if (planea_entries != 0)
-			DRM_DEBUG("plane A needs more FIFO entries\n");
-		awm = 1;
-	}
-	if (bwm <= 0) {
-		if (planeb_entries != 0)
-			DRM_DEBUG("plane B needs more FIFO entries\n");
-		bwm = 1;
-	}
+	planea_wm = intel_calculate_wm(planea_clock, &planea_params,
+				       pixel_size, latency_ns);
+	planeb_wm = intel_calculate_wm(planeb_clock, &planeb_params,
+				       pixel_size, latency_ns);
+	DRM_DEBUG("FIFO watermarks - A: %d, B: %d\n", planea_wm, planeb_wm);
 
 	/*
 	 * Overlay gets an aggressive default since video jitter is bad.
 	 */
 	cwm = 2;
 
-	/* Calc sr entries for one pipe configs */
+	/* Calc sr entries for one plane configs */
 	if (!planea_clock || !planeb_clock) {
+		/* self-refresh has much higher latency */
+		const static int sr_latency_ns = 6000;
+
 		sr_clock = planea_clock ? planea_clock : planeb_clock;
-		line_time_us = (sr_hdisplay * 1000) / sr_clock;
-		sr_entries = (((latency_ns / line_time_us) + 1) * pixel_size *
-			      sr_hdisplay) / 1000;
-		sr_entries = roundup(sr_entries / wm_params->cacheline_size, 1);
-		if (sr_entries < wm_params->fifo_size)
-			srwm = wm_params->fifo_size - sr_entries;
+		line_time_us = ((sr_hdisplay * 1000) / sr_clock);
+
+		/* Use ns/us then divide to preserve precision */
+		sr_entries = (((sr_latency_ns / line_time_us) + 1) *
+			      pixel_size * sr_hdisplay) / 1000;
+		sr_entries = roundup(sr_entries / cacheline_size, 1);
+		DRM_DEBUG("self-refresh entries: %d\n", sr_entries);
+		srwm = total_size - sr_entries;
+		if (srwm < 0)
+			srwm = 1;
 	}
 
 	DRM_DEBUG("Setting FIFO watermarks - A: %d, B: %d, C: %d, SR %d\n",
-		  awm, bwm, cwm, srwm);
+		  planea_wm, planeb_wm, cwm, srwm);
 
-	fwater_lo = fwater_lo | ((bwm & 0x3f) << 16) | (awm & 0x3f);
-	fwater_hi = fwater_hi | (cwm & 0x1f);
+	fwater_lo = ((planeb_wm & 0x3f) << 16) | (planea_wm & 0x3f);
+	fwater_hi = (cwm & 0x1f);
+
+	/* Set request length to 8 cachelines per fetch */
+	fwater_lo = fwater_lo | (1 << 24) | (1 << 8);
+	fwater_hi = fwater_hi | (1 << 8);
 
 	I915_WRITE(FW_BLC, fwater_lo);
 	I915_WRITE(FW_BLC2, fwater_hi);
 	if (IS_I9XX(dev))
-		I915_WRITE(FW_BLC_SELF, FW_BLC_SELF_EN | (srwm & 0x3f));
+		I915_WRITE(FW_BLC_SELF, (srwm & 0x3f));
 }
 
 static void i830_update_wm(struct drm_device *dev, int planea_clock,
 			   int pixel_size)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	uint32_t dsparb = I915_READ(DSPARB);
 	uint32_t fwater_lo = I915_READ(FW_BLC) & MM_FIFO_WATERMARK;
-	unsigned int asize, awm;
-	int planea_entries;
-
-	planea_entries = intel_calculate_wm(planea_clock, &i830_wm_info,
-					    pixel_size, latency_ns);
-
-	asize = dsparb & 0x7f;
+	int planea_wm;
 
-	awm = asize - planea_entries;
+	i830_wm_info.fifo_size = intel_get_fifo_size(dev, 0);
 
-	fwater_lo = fwater_lo | awm;
+	planea_wm = intel_calculate_wm(planea_clock, &i830_wm_info,
+				       pixel_size, latency_ns);
+	fwater_lo = fwater_lo | planea_wm;
 
 	I915_WRITE(FW_BLC, fwater_lo);
 }
@@ -1984,7 +2022,7 @@ static void intel_update_watermarks(struct drm_device *dev)
 	if (enabled <= 0)
 		return;
 
-	/* Single pipe configs can enable self refresh */
+	/* Single plane configs can enable self refresh */
 	if (enabled == 1 && IS_IGD(dev))
 		igd_enable_cxsr(dev, sr_clock, pixel_size);
 	else if (IS_IGD(dev))