gpu: nvgpu: cache gpu clk rate

Cache the rate used in clk_set_rate().
Return that cached rate on clk_get_rate(), don't read from hardware.
This cached rate is used to avoid duplicate requests to clk_set_rate().

Motivation is to support multiple governors for gpu clk.
Reading clock from hardware is unreliable in multi-governor situation.
Relying on hardware clock value could mislead the kernel gpu governor
in its scaling calculations.

Bug 2051688

Change-Id: I43fc056eea6f69fe0889c45640fcb892b658071c
Signed-off-by: Arun Kannan <akannan@nvidia.com>
(cherry picked from commit 7f819a9ba707e6e905168b00b0f3bf6348e86188)
Reviewed-on: https://git-master.nvidia.com/r/1662759
Reviewed-on: https://git-master.nvidia.com/r/1668919
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/clk_gk20a.h b/drivers/gpu/nvgpu/gk20a/clk_gk20a.h
index ec7022aa..d84e5969 100644
--- a/drivers/gpu/nvgpu/gk20a/clk_gk20a.h
+++ b/drivers/gpu/nvgpu/gk20a/clk_gk20a.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011 - 2017, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2011 - 2018, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -96,6 +96,9 @@ struct clk_gk20a {
 #if defined(CONFIG_COMMON_CLK)
         struct clk *tegra_clk;
         struct clk_hw hw;
+
+        /* scaling rate */
+        unsigned long cached_rate;
 #endif
         struct pll gpc_pll;
         struct pll gpc_pll_last;