drm/i915: add min freq control to debugfs

This makes for easier benchmarking and testing.  One can set a fixed
frequency by setting min and max to the same value.

v2: fix whitespace & comment (Eugeni)
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Eugeni Dodonov <eugeni@dodonov.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1764,6 +1764,64 @@ static const struct file_operations i915_max_freq_fops = {
 	.llseek = default_llseek,
 };
 
+static ssize_t
+i915_min_freq_read(struct file *filp, char __user *ubuf, size_t max,
+		   loff_t *ppos)
+{
+	struct drm_device *dev = filp->private_data;
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	char buf[80];
+	int len;
+
+	len = snprintf(buf, sizeof(buf),
+		       "min freq: %d\n", dev_priv->min_delay * 50);
+
+	if (len > sizeof(buf))
+		len = sizeof(buf);
+
+	return simple_read_from_buffer(ubuf, max, ppos, buf, len);
+}
+
+static ssize_t
+i915_min_freq_write(struct file *filp, const char __user *ubuf, size_t cnt,
+		    loff_t *ppos)
+{
+	struct drm_device *dev = filp->private_data;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	char buf[20];
+	int val = 1;
+
+	if (cnt > 0) {
+		if (cnt > sizeof(buf) - 1)
+			return -EINVAL;
+
+		if (copy_from_user(buf, ubuf, cnt))
+			return -EFAULT;
+		buf[cnt] = 0;
+
+		val = simple_strtoul(buf, NULL, 0);
+	}
+
+	DRM_DEBUG_DRIVER("Manually setting min freq to %d\n", val);
+
+	/*
+	 * Turbo will still be enabled, but won't go below the set value.
+	 */
+	dev_priv->min_delay = val / 50;
+
+	gen6_set_rps(dev, val / 50);
+
+	return cnt;
+}
+
+static const struct file_operations i915_min_freq_fops = {
+	.owner = THIS_MODULE,
+	.open = simple_open,
+	.read = i915_min_freq_read,
+	.write = i915_min_freq_write,
+	.llseek = default_llseek,
+};
+
 static ssize_t
 i915_cache_sharing_read(struct file *filp,
 		   char __user *ubuf,
@@ -1996,6 +2054,12 @@ int i915_debugfs_init(struct drm_minor *minor)
 	if (ret)
 		return ret;
 
+	ret = i915_debugfs_create(minor->debugfs_root, minor,
+				  "i915_min_freq",
+				  &i915_min_freq_fops);
+	if (ret)
+		return ret;
+
 	ret = i915_debugfs_create(minor->debugfs_root, minor,
 				  "i915_cache_sharing",
 				  &i915_cache_sharing_fops);
@@ -2028,6 +2092,8 @@ void i915_debugfs_cleanup(struct drm_minor *minor)
 				 1, minor);
 	drm_debugfs_remove_files((struct drm_info_list *) &i915_max_freq_fops,
 				 1, minor);
+	drm_debugfs_remove_files((struct drm_info_list *) &i915_min_freq_fops,
+				 1, minor);
 	drm_debugfs_remove_files((struct drm_info_list *) &i915_cache_sharing_fops,
 				 1, minor);
 	drm_debugfs_remove_files((struct drm_info_list *) &i915_ring_stop_fops,