gpu: nvgpu: fix debugfs to disable big pages

After setting 'Y' in disable_bigpage, in native SMMU case,
we could still see 64K GMMU pages beeing used.

Fixed the following:
    - enforce disable_bigpage in nvgpu_vm_map
    - update GPU characteristics so that new clients know
      whether or not big pages are enabled. For instance
      this may affect how CUDA requests memory mapping.

JIRA EVLR-1694

Change-Id: I62841096add3bd798c5c11090054f82c8a2be832
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1532429
Reviewed-by: Richard Zhao <rizhao@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

drivers/gpu/nvgpu/common/linux/debug.c

@@ -28,6 +28,7 @@
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/uaccess.h>
 
 #include <nvgpu/debug.h>
 
@@ -173,6 +174,45 @@ void gk20a_debug_show_dump(struct gk20a *g, struct gk20a_debug_output *o)
 	gk20a_debug_dump_all_channel_status_ramfc(g, o);
 }
 
+static ssize_t disable_bigpage_read(struct file *file, char __user *user_buf, size_t count, loff_t *ppos)
+{
+	char buf[3];
+	struct gk20a *g = file->private_data;
+
+	if (g->mm.disable_bigpage)
+		buf[0] = 'Y';
+	else
+		buf[0] = 'N';
+	buf[1] = '\n';
+	buf[2] = 0x00;
+	return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
+}
+
+static ssize_t disable_bigpage_write(struct file *file, const char __user *user_buf, size_t count, loff_t *ppos)
+{
+	char buf[32];
+	int buf_size;
+	bool bv;
+	struct gk20a *g = file->private_data;
+
+	buf_size = min(count, (sizeof(buf)-1));
+	if (copy_from_user(buf, user_buf, buf_size))
+		return -EFAULT;
+
+	if (strtobool(buf, &bv) == 0) {
+		g->mm.disable_bigpage = bv;
+		gk20a_init_gpu_characteristics(g);
+	}
+
+	return count;
+}
+
+static struct file_operations disable_bigpage_fops = {
+	.open =		simple_open,
+	.read =		disable_bigpage_read,
+	.write =	disable_bigpage_write,
+};
+
 static int railgate_residency_show(struct seq_file *s, void *data)
 {
 	struct gk20a *g = s->private;
@@ -296,10 +336,11 @@ void gk20a_debug_init(struct gk20a *g, const char *debugfs_symlink)
 					l->debugfs,
 					&g->mm.bypass_smmu);
 	l->debugfs_disable_bigpage =
-			debugfs_create_bool("disable_bigpage",
+			debugfs_create_file("disable_bigpage",
 					S_IRUGO|S_IWUSR,
 					l->debugfs,
-					&g->mm.disable_bigpage);
+					g,
+					&disable_bigpage_fops);
 
 	l->debugfs_timeslice_low_priority_us =
 			debugfs_create_u32("timeslice_low_priority_us",

drivers/gpu/nvgpu/common/linux/vm.c

@@ -260,6 +260,9 @@ u64 nvgpu_vm_map(struct vm_gk20a *vm,
 		map_offset = offset_align;
 
 	bfr.align = nvgpu_get_buffer_alignment(g, sgl, aperture);
+	if (g->mm.disable_bigpage)
+		bfr.pgsz_idx = gmmu_page_size_small;
+	else
 		bfr.pgsz_idx = __get_pte_size(vm, map_offset,
 				      min_t(u64, bfr.size, bfr.align));
 	mapping_size = mapping_size ? mapping_size : bfr.size;