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>

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");

drivers/gpu/nvgpu/os/linux/driver_common.c

@@ -66,6 +66,9 @@ static void nvgpu_init_vars(struct gk20a *g)
 	nvgpu_mutex_init(&g->tpc_pg_lock);
 	nvgpu_mutex_init(&g->clk_arb_enable_lock);
 
+	/* Init the clock req count to 0 */
+	nvgpu_atomic_set(&g->clk_arb_global_nr, 0);
+
 	l->regs_saved = l->regs;
 	l->bar1_saved = l->bar1;
 

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);

drivers/gpu/nvgpu/os/linux/scale.c

@@ -25,6 +25,7 @@
 
 #include <nvgpu/kmem.h>
 #include <nvgpu/log.h>
+#include <nvgpu/clk_arb.h>
 
 #include "gk20a/gk20a.h"
 #include "platform_gk20a.h"
@@ -154,6 +155,8 @@ static int gk20a_scale_target(struct device *dev, unsigned long *freq,
 	unsigned long rounded_rate;
 	unsigned long min_freq = 0, max_freq = 0;
 
+	if (nvgpu_clk_arb_has_active_req(g))
+		return 0;
 	/*
 	 * Calculate floor and cap frequency values
 	 *