Nouveau - Aug 2015 - [PATCH v2 17/22] drm/nouveau/timer: Fall back to kernel timer if GPU timer read failed

Unloading the nouveau module while the GPU is asleep (e.g. on dual GPU
laptops) leads to an infinite loop in nvkm_timer_wait_eq() because the
timer read out is 0xffffffffffffffff so the condition of the while loop
becomes -1 - (-1) < nsec and stays like that unless the GPU is woken up.

Use the kernel timer as fallback in this unlikely event. Synchronize the
kernel timer and GPU timer in nv04_timer_init() / gk20a_timer_init()
which should get called once on driver initialization and on every
resume.

Even with this fix applied, unloading the module takes a whopping
167 seconds. This could be reduced by changing the NV_WAIT_DEFAULT
timeout from the current (maybe excessive?) 2 seconds to 200 ms.

A WARN_ON is spewed out at nouveau_bo.c:398 after 81 seconds and
a null pointer dereference occurs in nouveau_cli_destroy(),
so there's more to fix here.

This patch might also be needed to properly handle a GPU connected
via Thunderbolt which is suddenly unplugged.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Paul Hordiienko <pvt.gord at gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno at bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]

Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c | 4 ++++
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c  | 9 +++++++++
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h  | 1 +
 3 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c
b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c
index 80e3806..28d27ff 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/gk20a.c
@@ -41,6 +41,10 @@ gk20a_timer_init(struct nvkm_object *object)
 	/* restore the time before suspend */
 	nv_wr32(priv, NV04_PTIMER_TIME_1, hi);
 	nv_wr32(priv, NV04_PTIMER_TIME_0, lo);
+
+	/* save kernel time as fallback */
+	priv->suspend_ktime = ktime_to_ns(ktime_get()) - priv->suspend_time;
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c
b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c
index 6b7facb..228749d 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.c
@@ -36,6 +36,11 @@ nv04_timer_read(struct nvkm_timer *ptimer)
 		lo = nv_rd32(priv, NV04_PTIMER_TIME_0);
 	} while (hi != nv_rd32(priv, NV04_PTIMER_TIME_1));
 
+	if (unlikely(hi == -1 && lo == -1)) {
+		nv_spam(priv, "read failed, falling back to kernel timer\n");
+		return ktime_to_ns(ktime_get()) - priv->suspend_ktime;
+	}
+
 	return ((u64)hi << 32 | lo);
 }
 
@@ -216,6 +221,10 @@ nv04_timer_init(struct nvkm_object *object)
 	nv_wr32(priv, NV04_PTIMER_INTR_EN_0, 0x00000000);
 	nv_wr32(priv, NV04_PTIMER_TIME_1, hi);
 	nv_wr32(priv, NV04_PTIMER_TIME_0, lo);
+
+	/* save kernel time as fallback */
+	priv->suspend_ktime = ktime_to_ns(ktime_get()) - priv->suspend_time;
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h
b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h
index 89996a9..1b83a0f 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/nv04.h
@@ -15,6 +15,7 @@ struct nv04_timer_priv {
 	struct list_head alarms;
 	spinlock_t lock;
 	u64 suspend_time;
+	u64 suspend_ktime;
 };
 
 int  nv04_timer_ctor(struct nvkm_object *, struct nvkm_object *,
-- 
1.8.5.2 (Apple Git-48)