From patchwork Tue Apr 7 02:11:16 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Todd Previte X-Patchwork-Id: 6166641 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 D80C09F2EC for ; Tue, 7 Apr 2015 02:11:26 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 142FD2034B for ; Tue, 7 Apr 2015 02:11:26 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id 245E0202B4 for ; Tue, 7 Apr 2015 02:11:25 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5655F6E382; Mon, 6 Apr 2015 19:11:24 -0700 (PDT) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-pd0-f176.google.com (mail-pd0-f176.google.com [209.85.192.176]) by gabe.freedesktop.org (Postfix) with ESMTP id 6A88A6E382; Mon, 6 Apr 2015 19:11:23 -0700 (PDT) Received: by pdea3 with SMTP id a3so62763275pde.3; Mon, 06 Apr 2015 19:11:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=8iqdH2Cdf3UBQ4+WiXHe+u0GlqfIJu023egEPCtRyMc=; b=N/HGdjSng/T/y2WwR68s/99ns98XLo7n9OiebUJeq0Uk8qS7hELjU7Bq5JLQPRycWY CoW8VEAujc1DjBTktV12z9UNbs3zG9BCbiljgGlhT8hHqTRCzA38+LQuS92rbz9825ro cZlYebfbvWHOTutcOEbdrBCaG+FnrM9BYa+lnAiBWde0ZdeaRQHeB1ByIsrEPrQeoY/k AWdLX4e5vmHgl26bAjOwFal4qHcllAUTaXG+uEIoJE3J74cCLVAUWg2MCXg722s5adXZ 0l+RzXw47b2ZpEkhbK3uPXgyQkSJEJjkiiOFhh5bkEBq/9sDS2sOS4dNekELwDgbZv59 yX8A== X-Received: by 10.70.103.10 with SMTP id fs10mr11273210pdb.141.1428372683254; Mon, 06 Apr 2015 19:11:23 -0700 (PDT) Received: from localhost.localdomain (ip70-162-72-208.ph.ph.cox.net. [70.162.72.208]) by mx.google.com with ESMTPSA id qc6sm6073130pdb.88.2015.04.06.19.11.22 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 06 Apr 2015 19:11:22 -0700 (PDT) From: Todd Previte To: intel-gfx@lists.freedesktop.org Subject: [PATCH 07/11] drm/i915: Fix for DP CTS test 4.2.2.5 - I2C DEFER handling Date: Mon, 6 Apr 2015 19:11:16 -0700 Message-Id: <1428372676-4784-1-git-send-email-tprevite@gmail.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1427822106-29617-8-git-send-email-tprevite@gmail.com> References: <1427822106-29617-8-git-send-email-tprevite@gmail.com> Cc: dri-devel@lists.freedesktop.org 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=-4.1 required=5.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_MED, T_DKIM_INVALID, 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 For test 4.2.2.5 to pass per the Link CTS Core 1.2 rev1.1 spec, the source device must attempt at least 7 times to read the EDID when it receives an I2C defer. The normal DRM code makes only 7 retries, regardless of whether or not the response is a native defer or an I2C defer. Test 4.2.2.5 fails since there are native defers interspersed with the I2C defers which results in less than 7 EDID read attempts. The solution is to decrement the retry counter when an I2C DEFER is returned such that another read attempt will be made. This situation should normally only occur in compliance testing, however, as a worse case real-world scenario, it would result in 13 attempts ( 6 native defers, 7 I2C defers) for a single transaction to complete. The net result is a slightly slower response to an EDID read that shouldn't significantly impact overall performance. V2: - Added a check on the number of I2C Defers to limit the number of times that the retries variable will be decremented. This is to address review feedback regarding possible infinite loops from misbehaving sink devices. Signed-off-by: Todd Previte Cc: dri-devel@lists.freedesktop.org --- drivers/gpu/drm/drm_dp_helper.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 79968e3..23025cf 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -469,6 +469,12 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg) case DP_AUX_I2C_REPLY_DEFER: DRM_DEBUG_KMS("I2C defer\n"); aux->i2c_defer_count++; + /* DP Compliance Test 4.2.2.5 Requirement: + * Must have at least 7 retries for I2C defers on the + * transaction to pass this test + */ + if (aux->i2c_defer_count < 8) + retry--; usleep_range(400, 500); continue;