drm/nouveau/tmr: calibrate for ns timestamps on init

We previously assumed (incorrectly a lot of the time) that PTIMER would
be programmed at a frequency which'd give its 64-bit timestamps in
nanoseconds.

By programming PTIMER ourselves, we avoid this problem.
Reviewed-by: Martin Peres <martin.peres@ensi-bourges.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv04_timer.c

@@ -3,46 +3,102 @@
 #include "nouveau_drv.h"
 #include "nouveau_drm.h"
 
+static u32
+nv04_crystal_freq(struct drm_device *dev)
+{
+	struct drm_nouveau_private *dev_priv = dev->dev_private;
+	u32 extdev_boot0 = nv_rd32(dev, 0x101000);
+	int type;
+
+	type = !!(extdev_boot0 & 0x00000040);
+	if ((dev_priv->chipset >= 0x17 && dev_priv->chipset < 0x20) ||
+	    dev_priv->chipset >= 0x25)
+		type |= (extdev_boot0 & 0x00400000) ? 2 : 0;
+
+	switch (type) {
+	case 0: return 13500000;
+	case 1: return 14318180;
+	case 2: return 27000000;
+	case 3: return 25000000;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
 int
 nv04_timer_init(struct drm_device *dev)
 {
+	struct drm_nouveau_private *dev_priv = dev->dev_private;
+	u32 m, n, d;
+
 	nv_wr32(dev, NV04_PTIMER_INTR_EN_0, 0x00000000);
 	nv_wr32(dev, NV04_PTIMER_INTR_0, 0xFFFFFFFF);
 
-	/* Just use the pre-existing values when possible for now; these regs
-	 * are not written in nv (driver writer missed a /4 on the address), and
-	 * writing 8 and 3 to the correct regs breaks the timings on the LVDS
-	 * hardware sequencing microcode.
-	 * A correct solution (involving calculations with the GPU PLL) can
-	 * be done when kernel modesetting lands
-	 */
-	if (!nv_rd32(dev, NV04_PTIMER_NUMERATOR) ||
-				!nv_rd32(dev, NV04_PTIMER_DENOMINATOR)) {
-		nv_wr32(dev, NV04_PTIMER_NUMERATOR, 0x00000008);
-		nv_wr32(dev, NV04_PTIMER_DENOMINATOR, 0x00000003);
+	/* aim for 31.25MHz, which gives us nanosecond timestamps */
+	d = 1000000000 / 32;
+
+	/* determine base clock for timer source */
+	if (dev_priv->chipset < 0x40) {
+		n = dev_priv->engine.pm.clock_get(dev, PLL_CORE);
+	} else
+	if (dev_priv->chipset == 0x40) {
+		/*XXX: figure this out */
+		n = 0;
+	} else {
+		n = nv04_crystal_freq(dev);
+		m = 1;
+		while (n < (d * 2)) {
+			n += (n / m);
+			m++;
+		}
+
+		nv_wr32(dev, 0x009220, m - 1);
 	}
 
+	if (!n) {
+		NV_WARN(dev, "PTIMER: unknown input clock freq\n");
+		if (!nv_rd32(dev, NV04_PTIMER_NUMERATOR) ||
+		    !nv_rd32(dev, NV04_PTIMER_DENOMINATOR)) {
+			nv_wr32(dev, NV04_PTIMER_NUMERATOR, 1);
+			nv_wr32(dev, NV04_PTIMER_DENOMINATOR, 1);
+		}
+		return 0;
+	}
+
+	/* reduce ratio to acceptable values */
+	while (((n % 5) == 0) && ((d % 5) == 0)) {
+		n /= 5;
+		d /= 5;
+	}
+
+	while (((n % 2) == 0) && ((d % 2) == 0)) {
+		n /= 2;
+		d /= 2;
+	}
+
+	while (n > 0xffff || d > 0xffff) {
+		n >>= 1;
+		d >>= 1;
+	}
+
+	nv_wr32(dev, NV04_PTIMER_NUMERATOR, n);
+	nv_wr32(dev, NV04_PTIMER_DENOMINATOR, d);
 	return 0;
 }
 
-uint64_t
+u64
 nv04_timer_read(struct drm_device *dev)
 {
-	uint32_t low;
-	/* From kmmio dumps on nv28 this looks like how the blob does this.
-	 * It reads the high dword twice, before and after.
-	 * The only explanation seems to be that the 64-bit timer counter
-	 * advances between high and low dword reads and may corrupt the
-	 * result. Not confirmed.
-	 */
-	uint32_t high2 = nv_rd32(dev, NV04_PTIMER_TIME_1);
-	uint32_t high1;
+	u32 hi, lo;
+
 	do {
-		high1 = high2;
-		low = nv_rd32(dev, NV04_PTIMER_TIME_0);
-		high2 = nv_rd32(dev, NV04_PTIMER_TIME_1);
-	} while (high1 != high2);
-	return (((uint64_t)high2) << 32) | (uint64_t)low;
+		hi = nv_rd32(dev, NV04_PTIMER_TIME_1);
+		lo = nv_rd32(dev, NV04_PTIMER_TIME_0);
+	} while (hi != nv_rd32(dev, NV04_PTIMER_TIME_1));
+
+	return ((u64)hi << 32 | lo);
 }
 
 void