drm/nouveau/instmem/gk20a: use direct CPU access

The Great Nouveau Refactoring Take II brought us a lot of goodness,
including acquire/release methods that are called before and after an
instobj is modified. These functions can be used as synchronization
points to manage CPU/GPU coherency if we modify an instobj using the
CPU.

This patch replaces the legacy and slow PRAMIN access for gk20a instmem
with CPU mappings and writes. A LRU list is used to unmap unused
mappings after a certain threshold (currently 1MB) of mapped instobjs is
reached. This allows mappings to be reused most of the time.

Accessing instobjs using the CPU requires to maintain the GPU L2 cache,
which we do in the acquire/release functions. This triggers a lot of L2
flushes/invalidates, but most of them are performed on an empty cache
(and thus return immediately), and overall context setup performance
greatly benefits from this (from 250ms to 160ms on Jetson TK1 for a
simple libdrm program).

Making L2 management more explicit should allow us to grab some more
performance in the future.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/subdev/instmem/gk20a.c

@@ -23,35 +23,42 @@
 /*
  * GK20A does not have dedicated video memory, and to accurately represent this
  * fact Nouveau will not create a RAM device for it. Therefore its instmem
- * implementation must be done directly on top of system memory, while providing
- * coherent read and write operations.
+ * implementation must be done directly on top of system memory, while
+ * preserving coherency for read and write operations.
  *
  * Instmem can be allocated through two means:
- * 1) If an IOMMU mapping has been probed, the IOMMU API is used to make memory
+ * 1) If an IOMMU unit has been probed, the IOMMU API is used to make memory
  *    pages contiguous to the GPU. This is the preferred way.
- * 2) If no IOMMU mapping is probed, the DMA API is used to allocate physically
+ * 2) If no IOMMU unit is probed, the DMA API is used to allocate physically
  *    contiguous memory.
  *
- * In both cases CPU read and writes are performed using PRAMIN (i.e. using the
- * GPU path) to ensure these operations are coherent for the GPU. This allows us
- * to use more "relaxed" allocation parameters when using the DMA API, since we
- * never need a kernel mapping.
+ * In both cases CPU read and writes are performed by creating a write-combined
+ * mapping. The GPU L2 cache must thus be flushed/invalidated when required. To
+ * be conservative we do this every time we acquire or release an instobj, but
+ * ideally L2 management should be handled at a higher level.
+ *
+ * To improve performance, CPU mappings are not removed upon instobj release.
+ * Instead they are placed into a LRU list to be recycled when the mapped space
+ * goes beyond a certain threshold. At the moment this limit is 1MB.
  */
-#define gk20a_instmem(p) container_of((p), struct gk20a_instmem, base)
 #include "priv.h"
 
 #include <core/memory.h>
 #include <core/mm.h>
 #include <core/tegra.h>
 #include <subdev/fb.h>
-
-#define gk20a_instobj(p) container_of((p), struct gk20a_instobj, memory)
+#include <subdev/ltc.h>
 
 struct gk20a_instobj {
 	struct nvkm_memory memory;
-	struct gk20a_instmem *imem;
 	struct nvkm_mem mem;
+	struct gk20a_instmem *imem;
+
+	/* CPU mapping */
+	u32 *vaddr;
+	struct list_head vaddr_node;
 };
+#define gk20a_instobj(p) container_of((p), struct gk20a_instobj, memory)
 
 /*
  * Used for objects allocated using the DMA API
@@ -59,10 +66,12 @@ struct gk20a_instobj {
 struct gk20a_instobj_dma {
 	struct gk20a_instobj base;
 
-	void *cpuaddr;
+	u32 *cpuaddr;
 	dma_addr_t handle;
 	struct nvkm_mm_node r;
 };
+#define gk20a_instobj_dma(p) \
+	container_of(gk20a_instobj(p), struct gk20a_instobj_dma, base)
 
 /*
  * Used for objects flattened using the IOMMU API
@@ -70,15 +79,24 @@ struct gk20a_instobj_dma {
 struct gk20a_instobj_iommu {
 	struct gk20a_instobj base;
 
-	/* array of base.mem->size pages */
+	/* will point to the higher half of pages */
+	dma_addr_t *dma_addrs;
+	/* array of base.mem->size pages (+ dma_addr_ts) */
 	struct page *pages[];
 };
+#define gk20a_instobj_iommu(p) \
+	container_of(gk20a_instobj(p), struct gk20a_instobj_iommu, base)
 
 struct gk20a_instmem {
 	struct nvkm_instmem base;
-	unsigned long lock_flags;
+
+	/* protects vaddr_* and gk20a_instobj::vaddr* */
 	spinlock_t lock;
-	u64 addr;
+
+	/* CPU mappings LRU */
+	unsigned int vaddr_use;
+	unsigned int vaddr_max;
+	struct list_head vaddr_lru;
 
 	/* Only used if IOMMU if present */
 	struct mutex *mm_mutex;
@@ -88,7 +106,10 @@ struct gk20a_instmem {
 
 	/* Only used by DMA API */
 	struct dma_attrs attrs;
+
+	void __iomem * (*cpu_map)(struct nvkm_memory *);
 };
+#define gk20a_instmem(p) container_of((p), struct gk20a_instmem, base)
 
 static enum nvkm_memory_target
 gk20a_instobj_target(struct nvkm_memory *memory)
@@ -100,7 +121,6 @@ static u64
 gk20a_instobj_addr(struct nvkm_memory *memory)
 {
 	return gk20a_instobj(memory)->mem.offset;
-
 }
 
 static u64
@@ -109,108 +129,218 @@ gk20a_instobj_size(struct nvkm_memory *memory)
 	return (u64)gk20a_instobj(memory)->mem.size << 12;
 }
 
+static void __iomem *
+gk20a_instobj_cpu_map_dma(struct nvkm_memory *memory)
+{
+	struct gk20a_instobj_dma *node = gk20a_instobj_dma(memory);
+	struct device *dev = node->base.imem->base.subdev.device->dev;
+	int npages = nvkm_memory_size(memory) >> 12;
+	struct page *pages[npages];
+	int i;
+
+	/* phys_to_page does not exist on all platforms... */
+	pages[0] = pfn_to_page(dma_to_phys(dev, node->handle) >> PAGE_SHIFT);
+	for (i = 1; i < npages; i++)
+		pages[i] = pages[0] + i;
+
+	return vmap(pages, npages, VM_MAP, pgprot_writecombine(PAGE_KERNEL));
+}
+
+static void __iomem *
+gk20a_instobj_cpu_map_iommu(struct nvkm_memory *memory)
+{
+	struct gk20a_instobj_iommu *node = gk20a_instobj_iommu(memory);
+	int npages = nvkm_memory_size(memory) >> 12;
+
+	return vmap(node->pages, npages, VM_MAP,
+		    pgprot_writecombine(PAGE_KERNEL));
+}
+
+/*
+ * Must be called while holding gk20a_instmem_lock
+ */
+static void
+gk20a_instmem_vaddr_gc(struct gk20a_instmem *imem, const u64 size)
+{
+	while (imem->vaddr_use + size > imem->vaddr_max) {
+		struct gk20a_instobj *obj;
+
+		/* no candidate that can be unmapped, abort... */
+		if (list_empty(&imem->vaddr_lru))
+			break;
+
+		obj = list_first_entry(&imem->vaddr_lru, struct gk20a_instobj,
+				       vaddr_node);
+		list_del(&obj->vaddr_node);
+		vunmap(obj->vaddr);
+		obj->vaddr = NULL;
+		imem->vaddr_use -= nvkm_memory_size(&obj->memory);
+		nvkm_debug(&imem->base.subdev, "(GC) vaddr used: %x/%x\n",
+			   imem->vaddr_use, imem->vaddr_max);
+
+	}
+}
+
 static void __iomem *
 gk20a_instobj_acquire(struct nvkm_memory *memory)
 {
-	struct gk20a_instmem *imem = gk20a_instobj(memory)->imem;
+	struct gk20a_instobj *node = gk20a_instobj(memory);
+	struct gk20a_instmem *imem = node->imem;
+	struct nvkm_ltc *ltc = imem->base.subdev.device->ltc;
+	const u64 size = nvkm_memory_size(memory);
 	unsigned long flags;
+
+	nvkm_ltc_flush(ltc);
+
 	spin_lock_irqsave(&imem->lock, flags);
-	imem->lock_flags = flags;
-	return NULL;
+
+	if (node->vaddr) {
+		/* remove us from the LRU list since we cannot be unmapped */
+		list_del(&node->vaddr_node);
+
+		goto out;
+	}
+
+	/* try to free some address space if we reached the limit */
+	gk20a_instmem_vaddr_gc(imem, size);
+
+	node->vaddr = imem->cpu_map(memory);
+
+	if (!node->vaddr) {
+		nvkm_error(&imem->base.subdev, "cannot map instobj - "
+			   "this is not going to end well...\n");
+		goto out;
+	}
+
+	imem->vaddr_use += size;
+	nvkm_debug(&imem->base.subdev, "vaddr used: %x/%x\n",
+		   imem->vaddr_use, imem->vaddr_max);
+
+out:
+	spin_unlock_irqrestore(&imem->lock, flags);
+
+	return node->vaddr;
 }
 
 static void
 gk20a_instobj_release(struct nvkm_memory *memory)
 {
-	struct gk20a_instmem *imem = gk20a_instobj(memory)->imem;
-	spin_unlock_irqrestore(&imem->lock, imem->lock_flags);
-}
+	struct gk20a_instobj *node = gk20a_instobj(memory);
+	struct gk20a_instmem *imem = node->imem;
+	struct nvkm_ltc *ltc = imem->base.subdev.device->ltc;
+	unsigned long flags;
 
-/*
- * Use PRAMIN to read/write data and avoid coherency issues.
- * PRAMIN uses the GPU path and ensures data will always be coherent.
- *
- * A dynamic mapping based solution would be desirable in the future, but
- * the issue remains of how to maintain coherency efficiently. On ARM it is
- * not easy (if possible at all?) to create uncached temporary mappings.
- */
+	spin_lock_irqsave(&imem->lock, flags);
+
+	/* add ourselves to the LRU list so our CPU mapping can be freed */
+	list_add_tail(&node->vaddr_node, &imem->vaddr_lru);
+
+	spin_unlock_irqrestore(&imem->lock, flags);
+
+	wmb();
+	nvkm_ltc_invalidate(ltc);
+}
 
 static u32
 gk20a_instobj_rd32(struct nvkm_memory *memory, u64 offset)
 {
 	struct gk20a_instobj *node = gk20a_instobj(memory);
-	struct gk20a_instmem *imem = node->imem;
-	struct nvkm_device *device = imem->base.subdev.device;
-	u64 base = (node->mem.offset + offset) & 0xffffff00000ULL;
-	u64 addr = (node->mem.offset + offset) & 0x000000fffffULL;
-	u32 data;
-
-	if (unlikely(imem->addr != base)) {
-		nvkm_wr32(device, 0x001700, base >> 16);
-		imem->addr = base;
-	}
-	data = nvkm_rd32(device, 0x700000 + addr);
-	return data;
+
+	return node->vaddr[offset / 4];
 }
 
 static void
 gk20a_instobj_wr32(struct nvkm_memory *memory, u64 offset, u32 data)
 {
 	struct gk20a_instobj *node = gk20a_instobj(memory);
-	struct gk20a_instmem *imem = node->imem;
-	struct nvkm_device *device = imem->base.subdev.device;
-	u64 base = (node->mem.offset + offset) & 0xffffff00000ULL;
-	u64 addr = (node->mem.offset + offset) & 0x000000fffffULL;
 
-	if (unlikely(imem->addr != base)) {
-		nvkm_wr32(device, 0x001700, base >> 16);
-		imem->addr = base;
-	}
-	nvkm_wr32(device, 0x700000 + addr, data);
+	node->vaddr[offset / 4] = data;
 }
 
 static void
 gk20a_instobj_map(struct nvkm_memory *memory, struct nvkm_vma *vma, u64 offset)
 {
 	struct gk20a_instobj *node = gk20a_instobj(memory);
+
 	nvkm_vm_map_at(vma, offset, &node->mem);
 }
 
+/*
+ * Clear the CPU mapping of an instobj if it exists
+ */
 static void
-gk20a_instobj_dtor_dma(struct gk20a_instobj *_node)
+gk20a_instobj_dtor(struct gk20a_instobj *node)
+{
+	struct gk20a_instmem *imem = node->imem;
+	struct gk20a_instobj *obj;
+	unsigned long flags;
+
+	spin_lock_irqsave(&imem->lock, flags);
+
+	if (!node->vaddr)
+		goto out;
+
+	list_for_each_entry(obj, &imem->vaddr_lru, vaddr_node) {
+		if (obj == node) {
+			list_del(&obj->vaddr_node);
+			break;
+		}
+	}
+	vunmap(node->vaddr);
+	node->vaddr = NULL;
+	imem->vaddr_use -= nvkm_memory_size(&node->memory);
+	nvkm_debug(&imem->base.subdev, "vaddr used: %x/%x\n",
+		   imem->vaddr_use, imem->vaddr_max);
+
+out:
+	spin_unlock_irqrestore(&imem->lock, flags);
+}
+
+static void *
+gk20a_instobj_dtor_dma(struct nvkm_memory *memory)
 {
-	struct gk20a_instobj_dma *node = (void *)_node;
-	struct gk20a_instmem *imem = _node->imem;
+	struct gk20a_instobj_dma *node = gk20a_instobj_dma(memory);
+	struct gk20a_instmem *imem = node->base.imem;
 	struct device *dev = imem->base.subdev.device->dev;
 
+	gk20a_instobj_dtor(&node->base);
+
 	if (unlikely(!node->cpuaddr))
-		return;
+		goto out;
 
-	dma_free_attrs(dev, _node->mem.size << PAGE_SHIFT, node->cpuaddr,
+	dma_free_attrs(dev, node->base.mem.size << PAGE_SHIFT, node->cpuaddr,
 		       node->handle, &imem->attrs);
+
+out:
+	return node;
 }
 
-static void
-gk20a_instobj_dtor_iommu(struct gk20a_instobj *_node)
+static void *
+gk20a_instobj_dtor_iommu(struct nvkm_memory *memory)
 {
-	struct gk20a_instobj_iommu *node = (void *)_node;
-	struct gk20a_instmem *imem = _node->imem;
+	struct gk20a_instobj_iommu *node = gk20a_instobj_iommu(memory);
+	struct gk20a_instmem *imem = node->base.imem;
+	struct device *dev = imem->base.subdev.device->dev;
 	struct nvkm_mm_node *r;
 	int i;
 
-	if (unlikely(list_empty(&_node->mem.regions)))
-		return;
+	gk20a_instobj_dtor(&node->base);
 
-	r = list_first_entry(&_node->mem.regions, struct nvkm_mm_node,
+	if (unlikely(list_empty(&node->base.mem.regions)))
+		goto out;
+
+	r = list_first_entry(&node->base.mem.regions, struct nvkm_mm_node,
 			     rl_entry);
 
 	/* clear bit 34 to unmap pages */
 	r->offset &= ~BIT(34 - imem->iommu_pgshift);
 
 	/* Unmap pages from GPU address space and free them */
-	for (i = 0; i < _node->mem.size; i++) {
+	for (i = 0; i < node->base.mem.size; i++) {
 		iommu_unmap(imem->domain,
 			    (r->offset + i) << imem->iommu_pgshift, PAGE_SIZE);
+		dma_unmap_page(dev, node->dma_addrs[i], PAGE_SIZE,
+			       DMA_BIDIRECTIONAL);
 		__free_page(node->pages[i]);
 	}
 
@@ -218,25 +348,27 @@ gk20a_instobj_dtor_iommu(struct gk20a_instobj *_node)
 	mutex_lock(imem->mm_mutex);
 	nvkm_mm_free(imem->mm, &r);
 	mutex_unlock(imem->mm_mutex);
-}
-
-static void *
-gk20a_instobj_dtor(struct nvkm_memory *memory)
-{
-	struct gk20a_instobj *node = gk20a_instobj(memory);
-	struct gk20a_instmem *imem = node->imem;
-
-	if (imem->domain)
-		gk20a_instobj_dtor_iommu(node);
-	else
-		gk20a_instobj_dtor_dma(node);
 
+out:
 	return node;
 }
 
 static const struct nvkm_memory_func
-gk20a_instobj_func = {
-	.dtor = gk20a_instobj_dtor,
+gk20a_instobj_func_dma = {
+	.dtor = gk20a_instobj_dtor_dma,
+	.target = gk20a_instobj_target,
+	.addr = gk20a_instobj_addr,
+	.size = gk20a_instobj_size,
+	.acquire = gk20a_instobj_acquire,
+	.release = gk20a_instobj_release,
+	.rd32 = gk20a_instobj_rd32,
+	.wr32 = gk20a_instobj_wr32,
+	.map = gk20a_instobj_map,
+};
+
+static const struct nvkm_memory_func
+gk20a_instobj_func_iommu = {
+	.dtor = gk20a_instobj_dtor_iommu,
 	.target = gk20a_instobj_target,
 	.addr = gk20a_instobj_addr,
 	.size = gk20a_instobj_size,
@@ -259,6 +391,8 @@ gk20a_instobj_ctor_dma(struct gk20a_instmem *imem, u32 npages, u32 align,
 		return -ENOMEM;
 	*_node = &node->base;
 
+	nvkm_memory_ctor(&gk20a_instobj_func_dma, &node->base.memory);
+
 	node->cpuaddr = dma_alloc_attrs(dev, npages << PAGE_SHIFT,
 					&node->handle, GFP_KERNEL,
 					&imem->attrs);
@@ -292,24 +426,40 @@ gk20a_instobj_ctor_iommu(struct gk20a_instmem *imem, u32 npages, u32 align,
 {
 	struct gk20a_instobj_iommu *node;
 	struct nvkm_subdev *subdev = &imem->base.subdev;
+	struct device *dev = subdev->device->dev;
 	struct nvkm_mm_node *r;
 	int ret;
 	int i;
 
-	if (!(node = kzalloc(sizeof(*node) +
-			     sizeof( node->pages[0]) * npages, GFP_KERNEL)))
+	/*
+	 * despite their variable size, instmem allocations are small enough
+	 * (< 1 page) to be handled by kzalloc
+	 */
+	if (!(node = kzalloc(sizeof(*node) + ((sizeof(node->pages[0]) +
+			     sizeof(*node->dma_addrs)) * npages), GFP_KERNEL)))
 		return -ENOMEM;
 	*_node = &node->base;
+	node->dma_addrs = (void *)(node->pages + npages);
+
+	nvkm_memory_ctor(&gk20a_instobj_func_iommu, &node->base.memory);
 
 	/* Allocate backing memory */
 	for (i = 0; i < npages; i++) {
 		struct page *p = alloc_page(GFP_KERNEL);
+		dma_addr_t dma_adr;
 
 		if (p == NULL) {
 			ret = -ENOMEM;
 			goto free_pages;
 		}
 		node->pages[i] = p;
+		dma_adr = dma_map_page(dev, p, 0, PAGE_SIZE, DMA_BIDIRECTIONAL);
+		if (dma_mapping_error(dev, dma_adr)) {
+			nvkm_error(subdev, "DMA mapping error!\n");
+			ret = -ENOMEM;
+			goto free_pages;
+		}
+		node->dma_addrs[i] = dma_adr;
 	}
 
 	mutex_lock(imem->mm_mutex);
@@ -318,16 +468,15 @@ gk20a_instobj_ctor_iommu(struct gk20a_instmem *imem, u32 npages, u32 align,
 			   align >> imem->iommu_pgshift, &r);
 	mutex_unlock(imem->mm_mutex);
 	if (ret) {
-		nvkm_error(subdev, "virtual space is full!\n");
+		nvkm_error(subdev, "IOMMU space is full!\n");
 		goto free_pages;
 	}
 
 	/* Map into GPU address space */
 	for (i = 0; i < npages; i++) {
-		struct page *p = node->pages[i];
 		u32 offset = (r->offset + i) << imem->iommu_pgshift;
 
-		ret = iommu_map(imem->domain, offset, page_to_phys(p),
+		ret = iommu_map(imem->domain, offset, node->dma_addrs[i],
 				PAGE_SIZE, IOMMU_READ | IOMMU_WRITE);
 		if (ret < 0) {
 			nvkm_error(subdev, "IOMMU mapping failure: %d\n", ret);
@@ -356,8 +505,13 @@ release_area:
 	mutex_unlock(imem->mm_mutex);
 
 free_pages:
-	for (i = 0; i < npages && node->pages[i] != NULL; i++)
+	for (i = 0; i < npages && node->pages[i] != NULL; i++) {
+		dma_addr_t dma_addr = node->dma_addrs[i];
+		if (dma_addr)
+			dma_unmap_page(dev, dma_addr, PAGE_SIZE,
+				       DMA_BIDIRECTIONAL);
 		__free_page(node->pages[i]);
+	}
 
 	return ret;
 }
@@ -367,8 +521,8 @@ gk20a_instobj_new(struct nvkm_instmem *base, u32 size, u32 align, bool zero,
 		  struct nvkm_memory **pmemory)
 {
 	struct gk20a_instmem *imem = gk20a_instmem(base);
-	struct gk20a_instobj *node = NULL;
 	struct nvkm_subdev *subdev = &imem->base.subdev;
+	struct gk20a_instobj *node = NULL;
 	int ret;
 
 	nvkm_debug(subdev, "%s (%s): size: %x align: %x\n", __func__,
@@ -388,7 +542,6 @@ gk20a_instobj_new(struct nvkm_instmem *base, u32 size, u32 align, bool zero,
 	if (ret)
 		return ret;
 
-	nvkm_memory_ctor(&gk20a_instobj_func, &node->memory);
 	node->imem = imem;
 
 	/* present memory for being mapped using small pages */
@@ -402,15 +555,25 @@ gk20a_instobj_new(struct nvkm_instmem *base, u32 size, u32 align, bool zero,
 	return 0;
 }
 
-static void
-gk20a_instmem_fini(struct nvkm_instmem *base)
+static void *
+gk20a_instmem_dtor(struct nvkm_instmem *base)
 {
-	gk20a_instmem(base)->addr = ~0ULL;
+	struct gk20a_instmem *imem = gk20a_instmem(base);
+
+	/* perform some sanity checks... */
+	if (!list_empty(&imem->vaddr_lru))
+		nvkm_warn(&base->subdev, "instobj LRU not empty!\n");
+
+	if (imem->vaddr_use != 0)
+		nvkm_warn(&base->subdev, "instobj vmap area not empty! "
+			  "0x%x bytes still mapped\n", imem->vaddr_use);
+
+	return imem;
 }
 
 static const struct nvkm_instmem_func
 gk20a_instmem = {
-	.fini = gk20a_instmem_fini,
+	.dtor = gk20a_instmem_dtor,
 	.memory_new = gk20a_instobj_new,
 	.persistent = true,
 	.zero = false,
@@ -429,23 +592,27 @@ gk20a_instmem_new(struct nvkm_device *device, int index,
 	spin_lock_init(&imem->lock);
 	*pimem = &imem->base;
 
+	/* do not allow more than 1MB of CPU-mapped instmem */
+	imem->vaddr_use = 0;
+	imem->vaddr_max = 0x100000;
+	INIT_LIST_HEAD(&imem->vaddr_lru);
+
 	if (tdev->iommu.domain) {
-		imem->domain = tdev->iommu.domain;
+		imem->mm_mutex = &tdev->iommu.mutex;
 		imem->mm = &tdev->iommu.mm;
+		imem->domain = tdev->iommu.domain;
 		imem->iommu_pgshift = tdev->iommu.pgshift;
-		imem->mm_mutex = &tdev->iommu.mutex;
+		imem->cpu_map = gk20a_instobj_cpu_map_iommu;
 
 		nvkm_info(&imem->base.subdev, "using IOMMU\n");
 	} else {
 		init_dma_attrs(&imem->attrs);
-		/*
-		 * We will access instmem through PRAMIN and thus do not need a
-		 * consistent CPU pointer or kernel mapping
-		 */
+		/* We will access the memory through our own mapping */
 		dma_set_attr(DMA_ATTR_NON_CONSISTENT, &imem->attrs);
 		dma_set_attr(DMA_ATTR_WEAK_ORDERING, &imem->attrs);
 		dma_set_attr(DMA_ATTR_WRITE_COMBINE, &imem->attrs);
 		dma_set_attr(DMA_ATTR_NO_KERNEL_MAPPING, &imem->attrs);
+		imem->cpu_map = gk20a_instobj_cpu_map_dma;
 
 		nvkm_info(&imem->base.subdev, "using DMA API\n");
 	}