From patchwork Wed Apr 13 14:58:32 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: 8823731 Return-Path: X-Original-To: patchwork-intel-gfx@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 7452FC0554 for ; Wed, 13 Apr 2016 14:59:20 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id A4D072026C for ; Wed, 13 Apr 2016 14:59:19 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id D5E4220382 for ; Wed, 13 Apr 2016 14:59:18 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 70CF56E912; Wed, 13 Apr 2016 14:59:14 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by gabe.freedesktop.org (Postfix) with ESMTPS id 85BD76E90F; Wed, 13 Apr 2016 14:59:10 +0000 (UTC) Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2C4587F6C1; Wed, 13 Apr 2016 14:59:10 +0000 (UTC) Received: from ecstaticemu.bos.redhat.com (dhcp-25-142.bos.redhat.com [10.18.25.142]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u3DEx5fH019844; Wed, 13 Apr 2016 10:59:09 -0400 From: Lyude To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Jani Nikula , =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Wed, 13 Apr 2016 10:58:32 -0400 Message-Id: <1460559513-32280-4-git-send-email-cpaul@redhat.com> In-Reply-To: <1460559513-32280-1-git-send-email-cpaul@redhat.com> References: <87d1pvt9ka.fsf@intel.com> <1460559513-32280-1-git-send-email-cpaul@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 Cc: David Airlie , open list Subject: [Intel-gfx] [PATCH v5 3/4] drm/dp_helper: Perform throw-away read before actual read in drm_dp_dpcd_read() X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, 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. Changes since v5 - If the throwaway read in drm_dp_dpcd_read() fails, return the error from that instead of continuing. This follows the same logic we do in drm_dp_dpcd_access() (e.g. the error from the first transaction may differ from the errors that proceeding attempts might return). Signed-off-by: Lyude --- drivers/gpu/drm/drm_dp_helper.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 540c3e4..aa80702 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -248,6 +248,18 @@ unlock: ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, void *buffer, size_t size) { + int ret; + + /* + * Sometimes we just get the same incorrect byte repeated over the + * entire buffer. Doing one throw away read initially seems to "solve" + * it. + */ + ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV, buffer, + 1); + if (ret != 1) + return ret; + return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer, size); }