Nouveau - Nov 2019 - [PATCH] RFC: drm/nouveau: Make BAR1 support optional

From: Thierry Reding <treding at nvidia.com>

The purpose of BAR1 is primarily to make memory accesses coherent.
However, some GPUs do not have BAR1 functionality. For example, the
GV11B found on the Xavier SoC is DMA coherent and therefore doesn't
need BAR1.

Implement a variant of FIFO channels that work without a mapping of
instance memory through BAR1.

XXX ensure memory barriers are in place for writes

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
Hi Ben,

I'm sending this a bit out of context (it's part of the larger series to
enable basic GV11B support) because I wanted to get some early feedback
from you on this.

For a bit of background: GV11B as it turns out doesn't really have BAR1
anymore. The SoC has a coherency fabric which means that basically the
GPU's system memory accesses are already coherent and hence we no longer
need to go via BAR1 to ensure that. Functionally the same can be done by
just writing to the memory via the CPU's virtual mapping.

So this patch implement basically a second variant of the FIFO channel
which, instead of taking a physical address and then ioremapping that,
takes a struct nvkm_memory object. This seems to work, though since I'm
not really doing much yet (firmware loading fails, etc.) I wouldn't call
this "done" just yet.

In fact there are a few things that I'm not happy about. For example I
think we'll eventually need to have barriers to ensure that the CPU
write buffers are flushed, etc. It also seems like most users of the
FIFO channel object will just go and map its buffer once and then only
access it via the virtual mapping only, without going through the
->rd32()/->wr32() callbacks nor unmapping via ->unmap(). That means we
effectively don't have a good point where we could emit the memory
barriers.

I see two possibilities here: 1) make all accesses go through the
accessors or 2) guard each series of accesses with a pair of nvkm_map()
and nvkm_done() calls. Both of those would mean that all code paths need
to be carefully audited.

One other thing I'm wondering is if it's okay to put all of this into
the gk104_fifo implementation. I think the result of parameterizing on
device->bar is pretty neat. Also, it seems like most of the rest of the
code would have to be duplicated, or a lot of the gk104_*() function
exported to a new implementation. So I'm not sure that it's really worth
it.

Thierry

 .../drm/nouveau/include/nvkm/engine/fifo.h    |   7 +-
 .../gpu/drm/nouveau/nvkm/engine/fifo/chan.c   | 157 ++++++++++++++++--
 .../gpu/drm/nouveau/nvkm/engine/fifo/chan.h   |   6 +
 .../gpu/drm/nouveau/nvkm/engine/fifo/gk104.c  |  29 +++-
 4 files changed, 180 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
b/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
index 4bd6e1e7c413..c0fb545efb2b 100644
--- a/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
+++ b/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
@@ -25,7 +25,12 @@ struct nvkm_fifo_chan {
 	struct nvkm_gpuobj *inst;
 	struct nvkm_gpuobj *push;
 	struct nvkm_vmm *vmm;
-	void __iomem *user;
+
+	union {
+		struct nvkm_memory *mem;
+		void __iomem *user;
+	};
+
 	u64 addr;
 	u32 size;
 
diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
index d83485385934..f47bc96bbb6d 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
@@ -310,7 +310,7 @@ nvkm_fifo_chan_init(struct nvkm_object *object)
 }
 
 static void *
-nvkm_fifo_chan_dtor(struct nvkm_object *object)
+__nvkm_fifo_chan_dtor(struct nvkm_object *object)
 {
 	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
 	struct nvkm_fifo *fifo = chan->fifo;
@@ -324,9 +324,6 @@ nvkm_fifo_chan_dtor(struct nvkm_object *object)
 	}
 	spin_unlock_irqrestore(&fifo->lock, flags);
 
-	if (chan->user)
-		iounmap(chan->user);
-
 	if (chan->vmm) {
 		nvkm_vmm_part(chan->vmm, chan->inst->memory);
 		nvkm_vmm_unref(&chan->vmm);
@@ -337,6 +334,17 @@ nvkm_fifo_chan_dtor(struct nvkm_object *object)
 	return data;
 }
 
+static void *
+nvkm_fifo_chan_dtor(struct nvkm_object *object)
+{
+	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
+
+	if (chan->user)
+		iounmap(chan->user);
+
+	return __nvkm_fifo_chan_dtor(object);
+}
+
 static const struct nvkm_object_func
 nvkm_fifo_chan_func = {
 	.dtor = nvkm_fifo_chan_dtor,
@@ -349,12 +357,98 @@ nvkm_fifo_chan_func = {
 	.sclass = nvkm_fifo_chan_child_get,
 };
 
+static void *
+nvkm_fifo_chan_mem_dtor(struct nvkm_object *object)
+{
+	return __nvkm_fifo_chan_dtor(object);
+}
+
+static int
+nvkm_fifo_chan_mem_map(struct nvkm_object *object, void *argv, u32 argc,
+		       enum nvkm_object_map *type, u64 *addr, u64 *size)
+{
+	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
+
+	pr_info("> %s(object=%px, argv=%px, argc=%u, type=%px, addr=%px,
size=%px)\n", __func__, object, argv, argc, type, addr, size);
+
+	*type = NVKM_OBJECT_MAP_VA;
+	*addr = (u64)nvkm_kmap(chan->mem);
+	*size = chan->size;
+
+	pr_info("  type: %d\n", *type);
+	pr_info("  addr: %016llx\n", *addr);
+	pr_info("  size: %016llx\n", *size);
+	pr_info("< %s()\n", __func__);
+	return 0;
+}
+
+static int
+nvkm_fifo_chan_mem_unmap(struct nvkm_object *object)
+{
+	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
+
+	pr_info("> %s(object=%px)\n", __func__, object);
+
+	nvkm_done(chan->mem);
+
+	pr_info("< %s()\n", __func__);
+	return 0;
+}
+
+static int
+nvkm_fifo_chan_mem_rd32(struct nvkm_object *object, u64 addr, u32 *data)
+{
+	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
+
+	pr_info("> %s(object=%px, addr=%016llx, data=%px)\n", __func__,
object, addr, data);
+
+	if (unlikely(addr + 4 > chan->size))
+		return -EINVAL;
+
+	*data = nvkm_ro32(chan->mem, addr);
+
+	pr_info("  data: %08x\n", *data);
+	pr_info("< %s()\n", __func__);
+	return 0;
+}
+
+static int
+nvkm_fifo_chan_mem_wr32(struct nvkm_object *object, u64 addr, u32 data)
+{
+	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
+
+	pr_info("> %s(object=%px, addr=%016llx, data=%08x)\n", __func__,
object, addr, data);
+
+	if (unlikely(addr + 4 > chan->size))
+		return -EINVAL;
+
+	nvkm_wo32(chan->mem, addr, data);
+
+	/* XXX add barrier */
+
+	pr_info("< %s()\n", __func__);
+	return 0;
+}
+
+static const struct nvkm_object_func
+nvkm_fifo_chan_mem_func = {
+	.dtor = nvkm_fifo_chan_mem_dtor,
+	.init = nvkm_fifo_chan_init,
+	.fini = nvkm_fifo_chan_fini,
+	.ntfy = nvkm_fifo_chan_ntfy,
+	.map = nvkm_fifo_chan_mem_map,
+	.unmap = nvkm_fifo_chan_mem_unmap,
+	.rd32 = nvkm_fifo_chan_mem_rd32,
+	.wr32 = nvkm_fifo_chan_mem_wr32,
+	.sclass = nvkm_fifo_chan_child_get,
+};
+
 int
-nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
-		    struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
-		    u64 hvmm, u64 push, u64 engines, int bar, u32 base,
-		    u32 user, const struct nvkm_oclass *oclass,
-		    struct nvkm_fifo_chan *chan)
+__nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
+		      struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
+		      u64 hvmm, u64 push, u64 engines,
+		      const struct nvkm_oclass *oclass,
+		      struct nvkm_fifo_chan *chan)
 {
 	struct nvkm_client *client = oclass->client;
 	struct nvkm_device *device = fifo->engine.subdev.device;
@@ -362,7 +456,6 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
 	unsigned long flags;
 	int ret;
 
-	nvkm_object_ctor(&nvkm_fifo_chan_func, oclass, &chan->object);
 	chan->func = func;
 	chan->fifo = fifo;
 	chan->engines = engines;
@@ -412,6 +505,26 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
 	__set_bit(chan->chid, fifo->mask);
 	spin_unlock_irqrestore(&fifo->lock, flags);
 
+	return 0;
+}
+
+int
+nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
+		    struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
+		    u64 hvmm, u64 push, u64 engines, int bar, u32 base,
+		    u32 user, const struct nvkm_oclass *oclass,
+		    struct nvkm_fifo_chan *chan)
+{
+	struct nvkm_device *device = fifo->engine.subdev.device;
+	int ret;
+
+	nvkm_object_ctor(&nvkm_fifo_chan_func, oclass, &chan->object);
+
+	ret = __nvkm_fifo_chan_ctor(func, fifo, size, align, zero, hvmm, push,
+				    engines, oclass, chan);
+	if (ret)
+		return ret;
+
 	/* determine address of this channel's user registers */
 	chan->addr = device->func->resource_addr(device, bar) +
 		     base + user * chan->chid;
@@ -420,3 +533,27 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
 	nvkm_fifo_cevent(fifo);
 	return 0;
 }
+
+int nvkm_fifo_chan_mem_ctor(const struct nvkm_fifo_chan_func *func,
+			    struct nvkm_fifo *fifo, u32 size, u32 align,
+			    bool zero, u64 hvmm, u64 push, u64 engines,
+			    struct nvkm_memory *mem, u32 user,
+			    const struct nvkm_oclass *oclass,
+			    struct nvkm_fifo_chan *chan)
+{
+	int ret;
+
+	nvkm_object_ctor(&nvkm_fifo_chan_mem_func, oclass, &chan->object);
+
+	ret = __nvkm_fifo_chan_ctor(func, fifo, size, align, zero, hvmm, push,
+				    engines, oclass, chan);
+	if (ret)
+		return ret;
+
+	chan->mem = mem;
+	chan->addr = user * chan->chid;
+	chan->size = user;
+
+	nvkm_fifo_cevent(fifo);
+	return 0;
+}
diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
index 177e10562600..71f32b1ebba0 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
@@ -24,6 +24,12 @@ int nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *,
struct nvkm_fifo *,
 			u32 size, u32 align, bool zero, u64 vm, u64 push,
 			u64 engines, int bar, u32 base, u32 user,
 			const struct nvkm_oclass *, struct nvkm_fifo_chan *);
+int nvkm_fifo_chan_mem_ctor(const struct nvkm_fifo_chan_func *,
+			    struct nvkm_fifo *, u32 size, u32 align,
+			    bool zero, u64 vm, u64 push, u64 engines,
+			    struct nvkm_memory *mem, u32 user,
+			    const struct nvkm_oclass *,
+			    struct nvkm_fifo_chan *);
 
 struct nvkm_fifo_chan_oclass {
 	int (*ctor)(struct nvkm_fifo *, const struct nvkm_oclass *,
diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
index 81cbe1cc4804..5404a182eb0a 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
@@ -906,7 +906,6 @@ gk104_fifo_oneinit(struct nvkm_fifo *base)
 	struct gk104_fifo *fifo = gk104_fifo(base);
 	struct nvkm_subdev *subdev = &fifo->base.engine.subdev;
 	struct nvkm_device *device = subdev->device;
-	struct nvkm_vmm *bar = nvkm_bar_bar1_vmm(device);
 	int engn, runl, pbid, ret, i, j;
 	enum nvkm_devidx engidx;
 	u32 *map;
@@ -967,12 +966,19 @@ gk104_fifo_oneinit(struct nvkm_fifo *base)
 	if (ret)
 		return ret;
 
-	ret = nvkm_vmm_get(bar, 12, nvkm_memory_size(fifo->user.mem),
-			   &fifo->user.bar);
-	if (ret)
-		return ret;
+	if (device->bar) {
+		struct nvkm_vmm *bar = nvkm_bar_bar1_vmm(device);
+
+		ret = nvkm_vmm_get(bar, 12, nvkm_memory_size(fifo->user.mem),
+				   &fifo->user.bar);
+		if (ret)
+			return ret;
+
+		return nvkm_memory_map(fifo->user.mem, 0, bar, fifo->user.bar,
+				       NULL, 0);
+	}
 
-	return nvkm_memory_map(fifo->user.mem, 0, bar, fifo->user.bar, NULL, 0);
+	return 0;
 }
 
 static void
@@ -998,7 +1004,12 @@ gk104_fifo_init(struct nvkm_fifo *base)
 		nvkm_wr32(device, 0x04014c + (i * 0x2000), 0xffffffff); /* INTREN */
 	}
 
-	nvkm_wr32(device, 0x002254, 0x10000000 | fifo->user.bar->addr >>
12);
+	/* obsolete on GV100 and later */
+	if (fifo->user.bar) {
+		u32 value = 0x10000000 | fifo->user.bar->addr >> 12;
+
+		nvkm_wr32(device, 0x002254, value);
+	}
 
 	if (fifo->func->pbdma->init_timeout)
 		fifo->func->pbdma->init_timeout(fifo);
@@ -1014,7 +1025,9 @@ gk104_fifo_dtor(struct nvkm_fifo *base)
 	struct nvkm_device *device = fifo->base.engine.subdev.device;
 	int i;
 
-	nvkm_vmm_put(nvkm_bar_bar1_vmm(device), &fifo->user.bar);
+	if (fifo->user.bar)
+		nvkm_vmm_put(nvkm_bar_bar1_vmm(device), &fifo->user.bar);
+
 	nvkm_memory_unref(&fifo->user.mem);
 
 	for (i = 0; i < fifo->runlist_nr; i++) {
-- 
2.23.0

On Fri, Nov 08, 2019 at 05:02:07PM +0100, Thierry Reding
wrote:
> From: Thierry Reding <treding at nvidia.com>
> 
> The purpose of BAR1 is primarily to make memory accesses coherent.
> However, some GPUs do not have BAR1 functionality. For example, the
> GV11B found on the Xavier SoC is DMA coherent and therefore doesn't
> need BAR1.
> 
> Implement a variant of FIFO channels that work without a mapping of
> instance memory through BAR1.
> 
> XXX ensure memory barriers are in place for writes
> 
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
> Hi Ben,
> 
> I'm sending this a bit out of context (it's part of the larger
series to
> enable basic GV11B support) because I wanted to get some early feedback
> from you on this.
> 
> For a bit of background: GV11B as it turns out doesn't really have BAR1
> anymore. The SoC has a coherency fabric which means that basically the
> GPU's system memory accesses are already coherent and hence we no
longer
> need to go via BAR1 to ensure that. Functionally the same can be done by
> just writing to the memory via the CPU's virtual mapping.
> 
> So this patch implement basically a second variant of the FIFO channel
> which, instead of taking a physical address and then ioremapping that,
> takes a struct nvkm_memory object. This seems to work, though since I'm
> not really doing much yet (firmware loading fails, etc.) I wouldn't
call
> this "done" just yet.
> 
> In fact there are a few things that I'm not happy about. For example I
> think we'll eventually need to have barriers to ensure that the CPU
> write buffers are flushed, etc. It also seems like most users of the
> FIFO channel object will just go and map its buffer once and then only
> access it via the virtual mapping only, without going through the
> ->rd32()/->wr32() callbacks nor unmapping via ->unmap(). That
means we
> effectively don't have a good point where we could emit the memory
> barriers.
> 
> I see two possibilities here: 1) make all accesses go through the
> accessors or 2) guard each series of accesses with a pair of nvkm_map()
> and nvkm_done() calls. Both of those would mean that all code paths need
> to be carefully audited.
Actually it looks like this is already working if I return 0 as the
address from the ->unmap() callback. That seems to result in the
->wr32() and ->rd32() callbacks getting called instead of the callers
trying to directly dereference the address, which obviously they now
can't.

So this seems like it could give me exactly what I need to make this
work. Again, this seems to get me past probe, but I see only a single
write at this point, so that's not saying much.

Thierry
> 
> One other thing I'm wondering is if it's okay to put all of this
into
> the gk104_fifo implementation. I think the result of parameterizing on
> device->bar is pretty neat. Also, it seems like most of the rest of the
> code would have to be duplicated, or a lot of the gk104_*() function
> exported to a new implementation. So I'm not sure that it's really
worth
> it.
> 
> Thierry
> 
>  .../drm/nouveau/include/nvkm/engine/fifo.h    |   7 +-
>  .../gpu/drm/nouveau/nvkm/engine/fifo/chan.c   | 157 ++++++++++++++++--
>  .../gpu/drm/nouveau/nvkm/engine/fifo/chan.h   |   6 +
>  .../gpu/drm/nouveau/nvkm/engine/fifo/gk104.c  |  29 +++-
>  4 files changed, 180 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
b/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
> index 4bd6e1e7c413..c0fb545efb2b 100644
> --- a/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
> +++ b/drivers/gpu/drm/nouveau/include/nvkm/engine/fifo.h
> @@ -25,7 +25,12 @@ struct nvkm_fifo_chan {
>  	struct nvkm_gpuobj *inst;
>  	struct nvkm_gpuobj *push;
>  	struct nvkm_vmm *vmm;
> -	void __iomem *user;
> +
> +	union {
> +		struct nvkm_memory *mem;
> +		void __iomem *user;
> +	};
> +
>  	u64 addr;
>  	u32 size;
>  
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
> index d83485385934..f47bc96bbb6d 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c
> @@ -310,7 +310,7 @@ nvkm_fifo_chan_init(struct nvkm_object *object)
>  }
>  
>  static void *
> -nvkm_fifo_chan_dtor(struct nvkm_object *object)
> +__nvkm_fifo_chan_dtor(struct nvkm_object *object)
>  {
>  	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
>  	struct nvkm_fifo *fifo = chan->fifo;
> @@ -324,9 +324,6 @@ nvkm_fifo_chan_dtor(struct nvkm_object *object)
>  	}
>  	spin_unlock_irqrestore(&fifo->lock, flags);
>  
> -	if (chan->user)
> -		iounmap(chan->user);
> -
>  	if (chan->vmm) {
>  		nvkm_vmm_part(chan->vmm, chan->inst->memory);
>  		nvkm_vmm_unref(&chan->vmm);
> @@ -337,6 +334,17 @@ nvkm_fifo_chan_dtor(struct nvkm_object *object)
>  	return data;
>  }
>  
> +static void *
> +nvkm_fifo_chan_dtor(struct nvkm_object *object)
> +{
> +	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
> +
> +	if (chan->user)
> +		iounmap(chan->user);
> +
> +	return __nvkm_fifo_chan_dtor(object);
> +}
> +
>  static const struct nvkm_object_func
>  nvkm_fifo_chan_func = {
>  	.dtor = nvkm_fifo_chan_dtor,
> @@ -349,12 +357,98 @@ nvkm_fifo_chan_func = {
>  	.sclass = nvkm_fifo_chan_child_get,
>  };
>  
> +static void *
> +nvkm_fifo_chan_mem_dtor(struct nvkm_object *object)
> +{
> +	return __nvkm_fifo_chan_dtor(object);
> +}
> +
> +static int
> +nvkm_fifo_chan_mem_map(struct nvkm_object *object, void *argv, u32 argc,
> +		       enum nvkm_object_map *type, u64 *addr, u64 *size)
> +{
> +	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
> +
> +	pr_info("> %s(object=%px, argv=%px, argc=%u, type=%px, addr=%px,
size=%px)\n", __func__, object, argv, argc, type, addr, size);
> +
> +	*type = NVKM_OBJECT_MAP_VA;
> +	*addr = (u64)nvkm_kmap(chan->mem);
> +	*size = chan->size;
> +
> +	pr_info("  type: %d\n", *type);
> +	pr_info("  addr: %016llx\n", *addr);
> +	pr_info("  size: %016llx\n", *size);
> +	pr_info("< %s()\n", __func__);
> +	return 0;
> +}
> +
> +static int
> +nvkm_fifo_chan_mem_unmap(struct nvkm_object *object)
> +{
> +	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
> +
> +	pr_info("> %s(object=%px)\n", __func__, object);
> +
> +	nvkm_done(chan->mem);
> +
> +	pr_info("< %s()\n", __func__);
> +	return 0;
> +}
> +
> +static int
> +nvkm_fifo_chan_mem_rd32(struct nvkm_object *object, u64 addr, u32 *data)
> +{
> +	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
> +
> +	pr_info("> %s(object=%px, addr=%016llx, data=%px)\n",
__func__, object, addr, data);
> +
> +	if (unlikely(addr + 4 > chan->size))
> +		return -EINVAL;
> +
> +	*data = nvkm_ro32(chan->mem, addr);
> +
> +	pr_info("  data: %08x\n", *data);
> +	pr_info("< %s()\n", __func__);
> +	return 0;
> +}
> +
> +static int
> +nvkm_fifo_chan_mem_wr32(struct nvkm_object *object, u64 addr, u32 data)
> +{
> +	struct nvkm_fifo_chan *chan = nvkm_fifo_chan(object);
> +
> +	pr_info("> %s(object=%px, addr=%016llx, data=%08x)\n",
__func__, object, addr, data);
> +
> +	if (unlikely(addr + 4 > chan->size))
> +		return -EINVAL;
> +
> +	nvkm_wo32(chan->mem, addr, data);
> +
> +	/* XXX add barrier */
> +
> +	pr_info("< %s()\n", __func__);
> +	return 0;
> +}
> +
> +static const struct nvkm_object_func
> +nvkm_fifo_chan_mem_func = {
> +	.dtor = nvkm_fifo_chan_mem_dtor,
> +	.init = nvkm_fifo_chan_init,
> +	.fini = nvkm_fifo_chan_fini,
> +	.ntfy = nvkm_fifo_chan_ntfy,
> +	.map = nvkm_fifo_chan_mem_map,
> +	.unmap = nvkm_fifo_chan_mem_unmap,
> +	.rd32 = nvkm_fifo_chan_mem_rd32,
> +	.wr32 = nvkm_fifo_chan_mem_wr32,
> +	.sclass = nvkm_fifo_chan_child_get,
> +};
> +
>  int
> -nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
> -		    struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
> -		    u64 hvmm, u64 push, u64 engines, int bar, u32 base,
> -		    u32 user, const struct nvkm_oclass *oclass,
> -		    struct nvkm_fifo_chan *chan)
> +__nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
> +		      struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
> +		      u64 hvmm, u64 push, u64 engines,
> +		      const struct nvkm_oclass *oclass,
> +		      struct nvkm_fifo_chan *chan)
>  {
>  	struct nvkm_client *client = oclass->client;
>  	struct nvkm_device *device = fifo->engine.subdev.device;
> @@ -362,7 +456,6 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func
*func,
>  	unsigned long flags;
>  	int ret;
>  
> -	nvkm_object_ctor(&nvkm_fifo_chan_func, oclass, &chan->object);
>  	chan->func = func;
>  	chan->fifo = fifo;
>  	chan->engines = engines;
> @@ -412,6 +505,26 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func
*func,
>  	__set_bit(chan->chid, fifo->mask);
>  	spin_unlock_irqrestore(&fifo->lock, flags);
>  
> +	return 0;
> +}
> +
> +int
> +nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func *func,
> +		    struct nvkm_fifo *fifo, u32 size, u32 align, bool zero,
> +		    u64 hvmm, u64 push, u64 engines, int bar, u32 base,
> +		    u32 user, const struct nvkm_oclass *oclass,
> +		    struct nvkm_fifo_chan *chan)
> +{
> +	struct nvkm_device *device = fifo->engine.subdev.device;
> +	int ret;
> +
> +	nvkm_object_ctor(&nvkm_fifo_chan_func, oclass, &chan->object);
> +
> +	ret = __nvkm_fifo_chan_ctor(func, fifo, size, align, zero, hvmm, push,
> +				    engines, oclass, chan);
> +	if (ret)
> +		return ret;
> +
>  	/* determine address of this channel's user registers */
>  	chan->addr = device->func->resource_addr(device, bar) +
>  		     base + user * chan->chid;
> @@ -420,3 +533,27 @@ nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func
*func,
>  	nvkm_fifo_cevent(fifo);
>  	return 0;
>  }
> +
> +int nvkm_fifo_chan_mem_ctor(const struct nvkm_fifo_chan_func *func,
> +			    struct nvkm_fifo *fifo, u32 size, u32 align,
> +			    bool zero, u64 hvmm, u64 push, u64 engines,
> +			    struct nvkm_memory *mem, u32 user,
> +			    const struct nvkm_oclass *oclass,
> +			    struct nvkm_fifo_chan *chan)
> +{
> +	int ret;
> +
> +	nvkm_object_ctor(&nvkm_fifo_chan_mem_func, oclass,
&chan->object);
> +
> +	ret = __nvkm_fifo_chan_ctor(func, fifo, size, align, zero, hvmm, push,
> +				    engines, oclass, chan);
> +	if (ret)
> +		return ret;
> +
> +	chan->mem = mem;
> +	chan->addr = user * chan->chid;
> +	chan->size = user;
> +
> +	nvkm_fifo_cevent(fifo);
> +	return 0;
> +}
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
> index 177e10562600..71f32b1ebba0 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.h
> @@ -24,6 +24,12 @@ int nvkm_fifo_chan_ctor(const struct nvkm_fifo_chan_func
*, struct nvkm_fifo *,
>  			u32 size, u32 align, bool zero, u64 vm, u64 push,
>  			u64 engines, int bar, u32 base, u32 user,
>  			const struct nvkm_oclass *, struct nvkm_fifo_chan *);
> +int nvkm_fifo_chan_mem_ctor(const struct nvkm_fifo_chan_func *,
> +			    struct nvkm_fifo *, u32 size, u32 align,
> +			    bool zero, u64 vm, u64 push, u64 engines,
> +			    struct nvkm_memory *mem, u32 user,
> +			    const struct nvkm_oclass *,
> +			    struct nvkm_fifo_chan *);
>  
>  struct nvkm_fifo_chan_oclass {
>  	int (*ctor)(struct nvkm_fifo *, const struct nvkm_oclass *,
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
> index 81cbe1cc4804..5404a182eb0a 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/fifo/gk104.c
> @@ -906,7 +906,6 @@ gk104_fifo_oneinit(struct nvkm_fifo *base)
>  	struct gk104_fifo *fifo = gk104_fifo(base);
>  	struct nvkm_subdev *subdev = &fifo->base.engine.subdev;
>  	struct nvkm_device *device = subdev->device;
> -	struct nvkm_vmm *bar = nvkm_bar_bar1_vmm(device);
>  	int engn, runl, pbid, ret, i, j;
>  	enum nvkm_devidx engidx;
>  	u32 *map;
> @@ -967,12 +966,19 @@ gk104_fifo_oneinit(struct nvkm_fifo *base)
>  	if (ret)
>  		return ret;
>  
> -	ret = nvkm_vmm_get(bar, 12, nvkm_memory_size(fifo->user.mem),
> -			   &fifo->user.bar);
> -	if (ret)
> -		return ret;
> +	if (device->bar) {
> +		struct nvkm_vmm *bar = nvkm_bar_bar1_vmm(device);
> +
> +		ret = nvkm_vmm_get(bar, 12, nvkm_memory_size(fifo->user.mem),
> +				   &fifo->user.bar);
> +		if (ret)
> +			return ret;
> +
> +		return nvkm_memory_map(fifo->user.mem, 0, bar, fifo->user.bar,
> +				       NULL, 0);
> +	}
>  
> -	return nvkm_memory_map(fifo->user.mem, 0, bar, fifo->user.bar,
NULL, 0);
> +	return 0;
>  }
>  
>  static void
> @@ -998,7 +1004,12 @@ gk104_fifo_init(struct nvkm_fifo *base)
>  		nvkm_wr32(device, 0x04014c + (i * 0x2000), 0xffffffff); /* INTREN */
>  	}
>  
> -	nvkm_wr32(device, 0x002254, 0x10000000 | fifo->user.bar->addr
>> 12);
> +	/* obsolete on GV100 and later */
> +	if (fifo->user.bar) {
> +		u32 value = 0x10000000 | fifo->user.bar->addr >> 12;
> +
> +		nvkm_wr32(device, 0x002254, value);
> +	}
>  
>  	if (fifo->func->pbdma->init_timeout)
>  		fifo->func->pbdma->init_timeout(fifo);
> @@ -1014,7 +1025,9 @@ gk104_fifo_dtor(struct nvkm_fifo *base)
>  	struct nvkm_device *device = fifo->base.engine.subdev.device;
>  	int i;
>  
> -	nvkm_vmm_put(nvkm_bar_bar1_vmm(device), &fifo->user.bar);
> +	if (fifo->user.bar)
> +		nvkm_vmm_put(nvkm_bar_bar1_vmm(device), &fifo->user.bar);
> +
>  	nvkm_memory_unref(&fifo->user.mem);
>  
>  	for (i = 0; i < fifo->runlist_nr; i++) {
> -- 
> 2.23.0
> 
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