gpu: nvgpu: nvgpu SGL implementation

The last major item preventing the core MM code in the nvgpu
driver from being platform agnostic is the usage of Linux
scattergather tables and scattergather lists. These data
structures are used throughout the mapping code to handle
discontiguous DMA allocations and also overloaded to represent
VIDMEM allocs.

The notion of a scatter gather table is crucial to a HW device
that can handle discontiguous DMA. The GPU has a MMU which
allows the GPU to do page gathering and present a virtually
contiguous buffer to the GPU HW. As a result it makes sense
for the GPU driver to use some sort of scatter gather concept
so maximize memory usage efficiency.

To that end this patch keeps the notion of a scatter gather
list but implements it in the nvgpu common code. It is based
heavily on the Linux SGL concept. It is a singly linked list
of blocks - each representing a chunk of memory. To map or
use a DMA allocation SW must iterate over each block in the
SGL.

This patch implements the most basic level of support for this
data structure. There are certainly easy optimizations that
could be done to speed up the current implementation. However,
this patches' goal is to simply divest the core MM code from
any last Linux'isms. Speed and efficiency come next.

Change-Id: Icf44641db22d87fa1d003debbd9f71b605258e42
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1530867
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/linux/nvgpu_mem.c

@@ -21,6 +21,7 @@
 #include <nvgpu/log.h>
 #include <nvgpu/bug.h>
 #include <nvgpu/enabled.h>
+#include <nvgpu/kmem.h>
 
 #include <nvgpu/linux/dma.h>
 
@@ -395,3 +396,116 @@ int __nvgpu_mem_create_from_pages(struct gk20a *g, struct nvgpu_mem *dest,
 
 	return 0;
 }
+
+static struct nvgpu_mem_sgl *__nvgpu_mem_sgl_dup(struct gk20a *g,
+						 struct nvgpu_mem_sgl *sgl)
+{
+	struct nvgpu_mem_sgl *head, *next;
+
+	head = nvgpu_kzalloc(g, sizeof(*sgl));
+	if (!head)
+		return NULL;
+
+	next = head;
+	while (true) {
+		nvgpu_log(g, gpu_dbg_sgl,
+			  "  phys: 0x%-12llx dma: 0x%-12llx len: 0x%llx",
+			  sgl->phys, sgl->dma, sgl->length);
+
+		next->dma    = sgl->dma;
+		next->phys   = sgl->phys;
+		next->length = sgl->length;
+		next->next   = NULL;
+
+		sgl = nvgpu_mem_sgl_next(sgl);
+		if (!sgl)
+			break;
+
+		next->next = nvgpu_kzalloc(g, sizeof(*sgl));
+		if (!next->next) {
+			nvgpu_mem_sgl_free(g, head);
+			return NULL;
+		}
+		next = next->next;
+	}
+
+	return head;
+}
+
+static struct nvgpu_mem_sgl *__nvgpu_mem_sgl_create_from_vidmem(
+	struct gk20a *g,
+	struct scatterlist *linux_sgl)
+{
+	struct nvgpu_page_alloc *vidmem_alloc;
+
+	vidmem_alloc = get_vidmem_page_alloc(linux_sgl);
+	if (!vidmem_alloc)
+		return NULL;
+
+	nvgpu_log(g, gpu_dbg_sgl, "Vidmem sgl:");
+
+	return __nvgpu_mem_sgl_dup(g, vidmem_alloc->sgl);
+}
+
+struct nvgpu_mem_sgl *nvgpu_mem_sgl_create(struct gk20a *g,
+					   struct sg_table *sgt)
+{
+	struct nvgpu_mem_sgl *head, *sgl, *next;
+	struct scatterlist *linux_sgl = sgt->sgl;
+
+	if (is_vidmem_page_alloc(sg_dma_address(linux_sgl)))
+		return __nvgpu_mem_sgl_create_from_vidmem(g, linux_sgl);
+
+	head = nvgpu_kzalloc(g, sizeof(*sgl));
+	if (!head)
+		return NULL;
+
+	nvgpu_log(g, gpu_dbg_sgl, "Making sgl:");
+
+	sgl = head;
+	while (true) {
+		sgl->dma    = sg_dma_address(linux_sgl);
+		sgl->phys   = sg_phys(linux_sgl);
+		sgl->length = linux_sgl->length;
+
+		/*
+		 * We don't like offsets in the pages here. This will cause
+		 * problems.
+		 */
+		if (WARN_ON(linux_sgl->offset)) {
+			nvgpu_mem_sgl_free(g, head);
+			return NULL;
+		}
+
+		nvgpu_log(g, gpu_dbg_sgl,
+			  "  phys: 0x%-12llx dma: 0x%-12llx len: 0x%llx",
+			  sgl->phys, sgl->dma, sgl->length);
+
+		/*
+		 * When there's no more SGL ents for the Linux SGL we are
+		 * done. Don't bother making any more SGL ents for the nvgpu
+		 * SGL.
+		 */
+		linux_sgl = sg_next(linux_sgl);
+		if (!linux_sgl)
+			break;
+
+		next = nvgpu_kzalloc(g, sizeof(*sgl));
+		if (!next) {
+			nvgpu_mem_sgl_free(g, head);
+			return NULL;
+		}
+
+		sgl->next = next;
+		sgl = next;
+	}
+
+	nvgpu_log(g, gpu_dbg_sgl, "Done!");
+	return head;
+}
+
+struct nvgpu_mem_sgl *nvgpu_mem_sgl_create_from_mem(struct gk20a *g,
+						    struct nvgpu_mem *mem)
+{
+	return nvgpu_mem_sgl_create(g, mem->priv.sgt);
+}