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, 3 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/os/linux/debug_clk_gm20b.c b/drivers/gpu/nvgpu/os/linux/debug_clk_gm20b.c
index 52eea83f..b8b95fd7 100644
--- a/drivers/gpu/nvgpu/os/linux/debug_clk_gm20b.c
+++ b/drivers/gpu/nvgpu/os/linux/debug_clk_gm20b.c
@@ -17,6 +17,7 @@
 #include <linux/seq_file.h>
 
 #include <nvgpu/io.h>
+#include <nvgpu/clk_arb.h>
 
 #include "gm20b/clk_gm20b.h"
 #include "os_linux.h"
@@ -33,6 +34,8 @@ static int rate_get(void *data, u64 *val)
 static int rate_set(void *data, u64 val)
 {
         struct gk20a *g = (struct gk20a *)data;
+        if (nvgpu_clk_arb_has_active_req(g))
+                return 0;
         return g->ops.clk.set_rate(g, CTRL_CLK_DOMAIN_GPCCLK, (u32)val);
 }
 DEFINE_SIMPLE_ATTRIBUTE(rate_fops, rate_get, rate_set, "%llu\n");