gpu: nvgpu: Simplify ref-counting on VMs

Simplify ref-counting on VMs: take a ref when a VM is bound to a
channel and drop a ref when a channel is freed.

Previously ref-counts were scattered over the driver. Also the CE
and CDE code would bind channels with custom rolled code. This was
because the gk20a_vm_bind_channel() function took an as_share as
the VM argument (the VM was then inferred from that as_share).
However, it is trivial to abtract that bit out and allow a central
bind channel function that just takes a VM and a channel.

Bug 1846718

Change-Id: I156aab259f6c7a2fa338408c6c4a3a464cd44a0c
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/1261886
Reviewed-by: Richard Zhao <rizhao@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/vgpu/mm_vgpu.c b/drivers/gpu/nvgpu/vgpu/mm_vgpu.c
index 76631b96..f97acd47 100644
--- a/drivers/gpu/nvgpu/vgpu/mm_vgpu.c
+++ b/drivers/gpu/nvgpu/vgpu/mm_vgpu.c
@@ -446,6 +446,9 @@ static int vgpu_vm_bind_channel(struct gk20a_as_share *as_share,
                 err = -ENOMEM;
         }
 
+        if (ch->vm)
+                gk20a_vm_get(ch->vm);
+
         return err;
 }