gpu: nvgpu: restrict devfreq during active clk_arb set requests

Restrict access to devfreq when there are active set requests in the
clk_arbiter. We make the following changes in the patch.

1) Add a global counter in the struct gk20a named clk_arb_global_nr which
is used to track the number of active set requests in the system.

2) Anytime a set request is successfully made by the userspace,
clk_arb_global_nr is incremented by 1 and during the completion of
request(releasing the corresponding file handle), clk_arb_global_nr is
decremented by 1.

3) gk20a_scale_target(invoked by devfreq to set the new frequency based
on load) atomically checks clk_arb_global_nr. If the value = 0, the
code simply continue or else if its > 0, it quits thus making devfreq
requests mutually exclusive with the clk_arbiter.

Bug 2061372

Change-Id: I5d19de03e45520f4ff8fccb97b1f1589d04c8ab8
Signed-off-by: Debarshi Dutta <ddutta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1790002
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/gp10b/clk_arb_gp10b.c b/drivers/gpu/nvgpu/gp10b/clk_arb_gp10b.c
index 4dcc3ca5..78fb1261 100644
--- a/drivers/gpu/nvgpu/gp10b/clk_arb_gp10b.c
+++ b/drivers/gpu/nvgpu/gp10b/clk_arb_gp10b.c
@@ -215,6 +215,9 @@ int gp10b_init_clk_arbiter(struct gk20a *g)
                 goto init_fail;
         }
 
+        /* This is set for the duration of the default req */
+        nvgpu_atomic_inc(&g->clk_arb_global_nr);
+
         nvgpu_clk_arb_worker_enqueue(g, &arb->update_arb_work_item);
 
         do {
@@ -224,6 +227,8 @@ int gp10b_init_clk_arbiter(struct gk20a *g)
                         nvgpu_atomic_read(&arb->req_nr) != 0, 0);
         } while (nvgpu_atomic_read(&arb->req_nr) == 0);
 
+        /* Once the default request is completed, reduce the usage count */
+        nvgpu_atomic_dec(&g->clk_arb_global_nr);
 
         return arb->status;