kdb, kms: Save and restore the LUT on atomic KMS enter/exit

When changing VTs non-atomically the kernel works in conjunction with
the Xserver in user space and receives the LUT information from the
Xserver via a system call.  When changing modes atomically for kdb,
this information must be saved and restored without disturbing user
space as if nothing ever happened.

There is a short cut used by this patch where gamma_store is used as
the save space.  If this turns out to be a problem in the future a
pre-allocated chunk of memory will be required for each crtc to save
and restore the LUT information.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
CC: Jesse Barnes <jbarnes@virtuousgeek.org>
CC: David Airlie <airlied@linux.ie>
CC: dri-devel@lists.freedesktop.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_fb_helper.c

@@ -242,6 +242,30 @@ static int drm_fb_helper_parse_command_line(struct drm_fb_helper *fb_helper)
 	return 0;
 }
 
+static void drm_fb_helper_save_lut_atomic(struct drm_crtc *crtc, struct drm_fb_helper *helper)
+{
+	uint16_t *r_base, *g_base, *b_base;
+	int i;
+
+	r_base = crtc->gamma_store;
+	g_base = r_base + crtc->gamma_size;
+	b_base = g_base + crtc->gamma_size;
+
+	for (i = 0; i < crtc->gamma_size; i++)
+		helper->funcs->gamma_get(crtc, &r_base[i], &g_base[i], &b_base[i], i);
+}
+
+static void drm_fb_helper_restore_lut_atomic(struct drm_crtc *crtc)
+{
+	uint16_t *r_base, *g_base, *b_base;
+
+	r_base = crtc->gamma_store;
+	g_base = r_base + crtc->gamma_size;
+	b_base = g_base + crtc->gamma_size;
+
+	crtc->funcs->gamma_set(crtc, r_base, g_base, b_base, 0, crtc->gamma_size);
+}
+
 int drm_fb_helper_debug_enter(struct fb_info *info)
 {
 	struct drm_fb_helper *helper = info->par;
@@ -260,6 +284,7 @@ int drm_fb_helper_debug_enter(struct fb_info *info)
 				continue;
 
 			funcs =	mode_set->crtc->helper_private;
+			drm_fb_helper_save_lut_atomic(mode_set->crtc, helper);
 			funcs->mode_set_base_atomic(mode_set->crtc,
 						    mode_set->fb,
 						    mode_set->x,
@@ -309,6 +334,7 @@ int drm_fb_helper_debug_leave(struct fb_info *info)
 			continue;
 		}
 
+		drm_fb_helper_restore_lut_atomic(mode_set->crtc);
 		funcs->mode_set_base_atomic(mode_set->crtc, fb, crtc->x,
 					    crtc->y, 0);
 	}