From patchwork Thu Mar 24 18:27:09 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: cpaul@redhat.com X-Patchwork-Id: 8663771 Return-Path: X-Original-To: patchwork-dri-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 4B5B39F326 for ; Thu, 24 Mar 2016 18:27:57 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 7AAF62038E for ; Thu, 24 Mar 2016 18:27:56 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id AD05B202AE for ; Thu, 24 Mar 2016 18:27:55 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A562F6E17D; Thu, 24 Mar 2016 18:27:29 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5AAFD88054; Thu, 24 Mar 2016 18:27:26 +0000 (UTC) Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id F04B4811A2; Thu, 24 Mar 2016 18:27:25 +0000 (UTC) Received: from ecstaticemu.bos.redhat.com (dhcp-25-74.bos.redhat.com [10.18.25.74]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u2OIRKdD019205; Thu, 24 Mar 2016 14:27:25 -0400 From: Lyude To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Subject: [PATCH v4 4/5] drm/dp_helper: Perform throw-away read before actual read in drm_dp_dpcd_read() Date: Thu, 24 Mar 2016 14:27:09 -0400 Message-Id: <1458844031-2032-5-git-send-email-cpaul@redhat.com> In-Reply-To: <1458844031-2032-1-git-send-email-cpaul@redhat.com> References: <1458761417-12165-1-git-send-email-cpaul@redhat.com> <1458844031-2032-1-git-send-email-cpaul@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 Cc: arthur.j.runyan@intel.com, open list , Lyude X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This is part of a patch series to migrate all of the workarounds for commonly seen behavior from bad sinks in intel_dp_dpcd_read_wake() to drm's DP helper. Some sinks will just return garbage for the first aux tranaction they receive when coming out of sleep mode, so we need to perform an additional read before the actual read to workaround this. Signed-off-by: Lyude --- drivers/gpu/drm/drm_dp_helper.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 86656ca..702c78a 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -244,6 +244,13 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request, ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, void *buffer, size_t size) { + /* + * Sometimes we just get the same incorrect byte repeated over the + * entire buffer. Doing one throw away read initially seems to "solve" + * it. + */ + drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV, buffer, 1); + return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer, size); }