drm: Add explicit acquire ctx handling around ->gamma_set

	struct drm_crtc *crtc;

	void *r_base, *g_base, *b_base;

	int size;

	struct drm_modeset_acquire_ctx ctx;

	int ret = 0;

	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;

	if (crtc->funcs->gamma_set == NULL) {

		ret = -ENOSYS;

		goto out;

	}

	if (crtc->funcs->gamma_set == NULL)

		return -ENOSYS;

	/* memcpy into gamma store */

	if (crtc_lut->gamma_size != crtc->gamma_size) {

		ret = -EINVAL;

	if (crtc_lut->gamma_size != crtc->gamma_size)

		return -EINVAL;

	drm_modeset_acquire_init(&ctx, 0);

	dev->mode_config.acquire_ctx = &ctx;

retry:

	ret = drm_modeset_lock_all_ctx(dev, &ctx);

	if (ret)

		goto out;

	}

	size = crtc_lut->gamma_size * (sizeof(uint16_t));

	r_base = crtc->gamma_store;

	ret = crtc->funcs->gamma_set(crtc, r_base, g_base, b_base, crtc->gamma_size);

out:

	drm_modeset_unlock_all(dev);

	if (ret == -EDEADLK) {

		drm_modeset_backoff(&ctx);

		goto retry;

	}

	drm_modeset_drop_locks(&ctx);

	drm_modeset_acquire_fini(&ctx);

	return ret;

}