drm: Only take crtc lock in get_gamma ioctl

We don't call into drivers at all here, this is enough. Also, we can
reduce the critical section a bit to simplify the code.
crtc->gamma_size is set up once at driver load and then invariant, so
also doesn't need any protection.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170403083304.9083-8-daniel.vetter@ffwll.ch

1 files changed, 6 insertions, 10 deletions

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index cc23b9a505c0..a32be59a72d1 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -295,19 +295,15 @@ int drm_mode_gamma_get_ioctl(struct drm_device *dev,
         if (!drm_core_check_feature(dev, DRIVER_MODESET))
                 return -EINVAL;
 
-        drm_modeset_lock_all(dev);
         crtc = drm_crtc_find(dev, crtc_lut->crtc_id);
-        if (!crtc) {
-                ret = -ENOENT;
-                goto out;
-        }
+        if (!crtc)
+                return -ENOENT;
 
         /* memcpy into gamma store */
-        if (crtc_lut->gamma_size != crtc->gamma_size) {
-                ret = -EINVAL;
-                goto out;
-        }
+        if (crtc_lut->gamma_size != crtc->gamma_size)
+                return -EINVAL;
 
+        drm_modeset_lock(&crtc->mutex, NULL);
         size = crtc_lut->gamma_size * (sizeof(uint16_t));
         r_base = crtc->gamma_store;
         if (copy_to_user((void __user *)(unsigned long)crtc_lut->red, r_base, size)) {
@@ -327,6 +323,6 @@ int drm_mode_gamma_get_ioctl(struct drm_device *dev,
                 goto out;
         }
 out:
-        drm_modeset_unlock_all(dev);
+        drm_modeset_unlock(&crtc->mutex);
         return ret;
 }