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>

2 files changed, 4 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/include/nvgpu/clk_arb.h b/drivers/gpu/nvgpu/include/nvgpu/clk_arb.h
index 81b1df1b..a04e3542 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/clk_arb.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/clk_arb.h
@@ -295,6 +295,8 @@ int nvgpu_clk_arb_worker_init(struct gk20a *g);
 
 int nvgpu_clk_arb_init_arbiter(struct gk20a *g);
 
+bool nvgpu_clk_arb_has_active_req(struct gk20a *g);
+
 int nvgpu_clk_arb_get_arbiter_clk_range(struct gk20a *g, u32 api_domain,
                 u16 *min_mhz, u16 *max_mhz);
 
diff --git a/drivers/gpu/nvgpu/include/nvgpu/gk20a.h b/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
index b8ca5754..5f875707 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/gk20a.h
@@ -1596,6 +1596,8 @@ struct gk20a {
 
         struct nvgpu_mutex clk_arb_enable_lock;
 
+        nvgpu_atomic_t clk_arb_global_nr;
+
         struct gk20a_ce_app ce_app;
 
         bool ltc_intr_en_illegal_compstat;