Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761116AbaJDAND (ORCPT ); Fri, 3 Oct 2014 20:13:03 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45718 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754797AbaJCVxO (ORCPT ); Fri, 3 Oct 2014 17:53:14 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiri Kosina , Daniel Vetter Subject: [PATCH 3.14 020/238] drm/i915: read HEAD register back in init_ring_common() to enforce ordering Date: Fri, 3 Oct 2014 14:28:55 -0700 Message-Id: <20141003212914.308105790@linuxfoundation.org> X-Mailer: git-send-email 2.1.2 In-Reply-To: <20141003212913.680985295@linuxfoundation.org> References: <20141003212913.680985295@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Kosina commit ece4a17d237a79f63fbfaf3f724a12b6d500555c upstream. Withtout this, ring initialization fails reliabily during resume with [drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head ffffff8804 tail 00000000 start 000e4000 This is not a complete fix, but it is verified to make the ring initialization failures during resume much less likely. We were not able to root-cause this bug (likely HW-specific to Gen4 chips) yet. This is therefore used as a ducttape before problem is fully understood and proper fix created, so that people don't suffer from completely unusable systems in the meantime. The discussion and debugging is happening at https://bugs.freedesktop.org/show_bug.cgi?id=76554 Signed-off-by: Jiri Kosina Signed-off-by: Daniel Vetter Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++ 1 file changed, 3 insertions(+) --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -475,6 +475,9 @@ static int init_ring_common(struct intel } } + /* Enforce ordering by reading HEAD register back */ + I915_READ_HEAD(ring); + /* Initialize the ring. This must happen _after_ we've cleared the ring * registers with the above sequence (the readback of the HEAD registers * also enforces ordering), otherwise the hw might lose the new ring -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/