gpu: nvgpu: Add sub-nvgpu_mem

Add an API for creating a special sub-nvgpu_mem struct. This struct
comes with some fairly important caveats but is very useful for the
semaphore code.

Also, make sure that in nvgpu_mem_begin() and nvgpu_mem_end() no
additional mappings are made if not necessary. More importantly during
nvgpu_mem_end() it would be possible to vunmap() a CPU mapping of a
DMA allocation that does not expect this to happen.

JIRA NVGPU-12
JIRA NVGPU-30

Change-Id: I579429da9ff7288488753a113bafc558e0f17a0f
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/1464077
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h b/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
index 1590ee7a..397e9ab1 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
@@ -49,6 +49,13 @@ struct nvgpu_mem {
         bool                                     skip_wmb;
 
         /*
+         * Set when a nvgpu_mem struct is not a "real" nvgpu_mem struct. Instead
+         * the struct is just a copy of another nvgpu_mem struct.
+         */
+#define NVGPU_MEM_FLAG_SHADOW_COPY               (1 << 0)
+        unsigned long                            mem_flags;
+
+        /*
          * Only populated for a sysmem allocation.
          */
         void                                    *cpu_va;
@@ -86,6 +93,42 @@ static inline const char *nvgpu_aperture_str(enum nvgpu_aperture aperture)
         return "UNKNOWN";
 }
 
+/**
+ * nvgpu_mem_create_from_mem - Create a new nvgpu_mem struct from an old one.
+ *
+ * @g          - The GPU.
+ * @dest       - Destination nvgpu_mem to hold resulting memory description.
+ * @src        - Source memory. Must be valid.
+ * @start_page - Starting page to use.
+ * @nr_pages   - Number of pages to place in the new nvgpu_mem.
+ *
+ * Create a new nvgpu_mem struct describing a subsection of the @src nvgpu_mem.
+ * This will create an nvpgu_mem object starting at @start_page and is @nr_pages
+ * long. This currently only works on SYSMEM nvgpu_mems. If this is called on a
+ * VIDMEM nvgpu_mem then this will return an error.
+ *
+ * There is a _major_ caveat to this API: if the source buffer is freed before
+ * the copy is freed then the copy will become invalid. This is a result from
+ * how typical DMA APIs work: we can't call free on the buffer multiple times.
+ * Nor can we call free on parts of a buffer. Thus the only way to ensure that
+ * the entire buffer is actually freed is to call free once on the source
+ * buffer. Since these nvgpu_mem structs are not ref-counted in anyway it is up
+ * to the caller of this API to _ensure_ that the resulting nvgpu_mem buffer
+ * from this API is freed before the source buffer. Otherwise there can and will
+ * be memory corruption.
+ *
+ * The resulting nvgpu_mem should be released with the nvgpu_dma_free() or the
+ * nvgpu_dma_unmap_free() function depending on whether or not the resulting
+ * nvgpu_mem has been mapped.
+ *
+ * This will return 0 on success. An error is returned if the resulting
+ * nvgpu_mem would not make sense or if a new scatter gather table cannot be
+ * created.
+ */
+int nvgpu_mem_create_from_mem(struct gk20a *g,
+                              struct nvgpu_mem *dest, struct nvgpu_mem *src,
+                              int start_page, int nr_pages);
+
 /*
  * Buffer accessors - wrap between begin() and end() if there is no permanent
  * kernel mapping for this buffer.