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, 1 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/os/linux/ioctl_clk_arb.c b/drivers/gpu/nvgpu/os/linux/ioctl_clk_arb.c
index 2d9946b1..ff1cc00a 100644
--- a/drivers/gpu/nvgpu/os/linux/ioctl_clk_arb.c
+++ b/drivers/gpu/nvgpu/os/linux/ioctl_clk_arb.c
@@ -436,6 +436,7 @@ int nvgpu_clk_arb_commit_request_fd(struct gk20a *g,
         clk_arb_dbg(g, "requested target = %u\n",
                 (u32)dev->gpc2clk_target_mhz);
 
+        nvgpu_atomic_inc(&g->clk_arb_global_nr);
         nvgpu_ref_get(&dev->refcount);
         nvgpu_spinlock_acquire(&session->session_lock);
         nvgpu_list_add(&dev->node, &session->targets);