drm: Initialize a linear gamma table by default

Code stolen from gma500.

This is just a minor bit of safety code that I spotted and figured it
might be useful if we put it into the core. This is to make the
get_gamma ioctl reflect likely reality even before the first set_gamma
ioctl call.

v2 on irc: Extend commit message per Maarten's suggestions.

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/1459331485-28376-2-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_crtc.c

@@ -5139,6 +5139,9 @@ EXPORT_SYMBOL(drm_mode_connector_attach_encoder);
 int drm_mode_crtc_set_gamma_size(struct drm_crtc *crtc,
 				 int gamma_size)
 {
+	uint16_t *r_base, *g_base, *b_base;
+	int i;
+
 	crtc->gamma_size = gamma_size;
 
 	crtc->gamma_store = kcalloc(gamma_size, sizeof(uint16_t) * 3,
@@ -5148,6 +5151,16 @@ int drm_mode_crtc_set_gamma_size(struct drm_crtc *crtc,
 		return -ENOMEM;
 	}
 
+	r_base = crtc->gamma_store;
+	g_base = r_base + gamma_size;
+	b_base = g_base + gamma_size;
+	for (i = 0; i < gamma_size; i++) {
+		r_base[i] = i << 8;
+		g_base[i] = i << 8;
+		b_base[i] = i << 8;
+	}
+
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_mode_crtc_set_gamma_size);

drivers/gpu/drm/gma500/psb_intel_display.c

@@ -491,7 +491,6 @@ void psb_intel_crtc_init(struct drm_device *dev, int pipe,
 	struct drm_psb_private *dev_priv = dev->dev_private;
 	struct gma_crtc *gma_crtc;
 	int i;
-	uint16_t *r_base, *g_base, *b_base;
 
 	/* We allocate a extra array of drm_connector pointers
 	 * for fbdev after the crtc */
@@ -519,16 +518,10 @@ void psb_intel_crtc_init(struct drm_device *dev, int pipe,
 	gma_crtc->pipe = pipe;
 	gma_crtc->plane = pipe;
 
-	r_base = gma_crtc->base.gamma_store;
-	g_base = r_base + 256;
-	b_base = g_base + 256;
 	for (i = 0; i < 256; i++) {
 		gma_crtc->lut_r[i] = i;
 		gma_crtc->lut_g[i] = i;
 		gma_crtc->lut_b[i] = i;
-		r_base[i] = i << 8;
-		g_base[i] = i << 8;
-		b_base[i] = i << 8;
 
 		gma_crtc->lut_adj[i] = 0;
 	}