gpu: nvgpu: alternative implementation of dma_buf_get/set_data

Historically, nvgpu has supported a struct gk20a_dmabuf_priv and
associated it with a dmabuf instance. This was aided by Nvmap's
dma_buf_set_drv_data() and dma_buf_get_drvdata() APIs. gk20a_dmabuf_priv
is used to store Comptag IDs i.e. (1 per 64 kb) as well as can store the
dmabuf attachments to avoid multiple attach/detach calls. dma_buf_set_drv_data()
allows Nvgpu to associate an instance of struct gk20a_dmabuf_priv with the instance
of the dmabuf and also provide a release callback to delete the
instance when the last reference to the dmabuf is put. Nvmap accomplishes
this by modifying the struct dma_buf_ops definition to include the
set_drv_data and get_drv_data callbacks in the kernel code.

The above approach won't work for upstream Kstable and Nvmap
plans to remove these APIs for upcoming newer downstream kernels as
well.

In order to implement the same functionality without depending on Nvmap,
Nvgpu will implement a release chaining mechanism. Dmabuf's 'ops' pointer
points to a constant struct and hence a whole copy of the ops is made
followed by altering the new copy's release pointer.

struct gk20a_dmabuf_priv stores the new copy and the dmabuf's 'ops' is
changed to point to this. This allows Nvgpu to retrieve
the corresponding gk20a_dmabuf_priv instance using container_of.

Nvgpu's custom release callback will invoke the original release
callback of the dmabuf's producer as a last step, thus completing the
full circle. In case, the driver is removed, Nvgpu restores the
dmabuf's 'ops' back to the original state. In order to accomplish this,
every instance of a struct nvgpu_os_linux maintains a linkedlist of the
gk20a_dma_buf instances. During the driver removal, this linkedlist is
traversed and the corresponding dmabuf's 'ops' pointer is put back to
its original state followed by freeing of this instance.

Nvgpu is a producer of dmabuf's for vidmem and needs
a way to check whether the given dmabuf belongs to itself.
Its no longer reliable to depend on a comparision of
the 'ops' pointer. Instead dmabuf_export_info() allows a name to be set by the
exporter and this can be used to compare with a memory location
that belongs to Nvgpu. Similarly for sysmem dmabufs, Nvmap makes a
similar change in the way it identifies whether a dmabuf belongs to
itself.

Removed NVGPU_DMABUF_HAS_DRVDATA and moved to a unified mechanism for
both downstream as well as upstream kernel.

Some of the other changes in this file include the following.
1) Deletion of dmabuf.c and moving its contents over to dmabuf_priv.c
2) Replacing gk20a_mm_pin_has_drvdata with nvgpu_mm_pin_privdata and
vice-versa for unpin.

Bug 2878569

Change-Id: Icf8e79b05a25ad5a85f478c3ee0fc1eb7747e22d
Signed-off-by: Debarshi Dutta <ddutta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2341001
Reviewed-by: automaticguardword <automaticguardword@nvidia.com>
Reviewed-by: Puneet Saxena <puneets@nvidia.com>
Reviewed-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-by: Vijayakumar Subbu <vsubbu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/os/linux/module.c

@@ -78,6 +78,7 @@
 #include "driver_common.h"
 #include "channel.h"
 #include "debug_pmgr.h"
+#include "dmabuf_priv.h"
 
 #ifdef CONFIG_NVGPU_SUPPORT_CDE
 #include "cde.h"
@@ -1713,6 +1714,9 @@ static int gk20a_probe(struct platform_device *dev)
 	if (err)
 		goto return_err;
 
+	nvgpu_mutex_init(&l->dmabuf_priv_list_lock);
+	nvgpu_init_list_node(&l->dmabuf_priv_list);
+
 	return 0;
 
 return_err:
@@ -1793,6 +1797,9 @@ static int __exit gk20a_remove(struct platform_device *pdev)
 
 	err = nvgpu_remove(dev, &nvgpu_class);
 
+	gk20a_dma_buf_priv_list_clear(l);
+	nvgpu_mutex_destroy(&l->dmabuf_priv_list_lock);
+
 	unregister_reboot_notifier(&l->nvgpu_reboot_nb);
 
 	set_gk20a(pdev, NULL);