gpu: nvgpu: Remove GPU MMIO access on power/rail gate

This is to weed out accesses to the GPU while it is gated. Otherwise
the accesses are silently dropped or cause a HW hang (on older chips).

Bug 1514949

Change-Id: Ice4cdb9f1f736978ebb3db847f39c7439bf98134
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/416339
Reviewed-by: Mitch Luban <mluban@nvidia.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/gk20a.c b/drivers/gpu/nvgpu/gk20a/gk20a.c
index 2310b81c..c72b8735 100644
--- a/drivers/gpu/nvgpu/gk20a/gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/gk20a.c
@@ -164,6 +164,32 @@ static inline u32 sim_readl(struct gk20a *g, u32 r)
         return readl(g->sim.regs+r);
 }
 
+/*
+ * Locks out the driver from accessing GPU registers. This prevents access to
+ * thse registers after the GPU has been clock or power gated. This should help
+ * find annoying bugs where register reads and writes are silently dropped
+ * after the GPU has been turned off. On older chips these reads and writes can
+ * also lock the entire CPU up.
+ */
+int gk20a_lockout_registers(struct gk20a *g)
+{
+        g->regs = NULL;
+        g->bar1 = NULL;
+
+        return 0;
+}
+
+/*
+ * Undoes gk20a_lockout_registers().
+ */
+int gk20a_restore_registers(struct gk20a *g)
+{
+        g->regs = g->regs_saved;
+        g->bar1 = g->bar1_saved;
+
+        return 0;
+}
+
 static void kunmap_and_free_iopage(void **kvaddr, struct page **page)
 {
         if (*kvaddr) {
@@ -676,6 +702,9 @@ static int gk20a_init_support(struct platform_device *dev)
                 goto fail;
         }
 
+        g->regs_saved = g->regs;
+        g->bar1_saved = g->bar1;
+
         /* Get interrupt numbers */
         g->irq_nonstall = platform_get_irq(dev, 1);
         if (g->irq_stall < 0 || g->irq_nonstall < 0) {
@@ -786,6 +815,9 @@ static int gk20a_pm_prepare_poweroff(struct device *dev)
 
         g->power_on = false;
 
+        /* Stop CPU from accessing the GPU registers. */
+        gk20a_lockout_registers(g);
+
         return ret;
 }
 
@@ -820,6 +852,10 @@ static int gk20a_pm_finalize_poweron(struct device *dev)
 
         trace_gk20a_finalize_poweron(dev_name(dev));
 
+        err = gk20a_restore_registers(g);
+        if (err)
+                return err;
+
         nice_value = task_nice(current);
         set_user_nice(current, -20);