From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3129C7618F for ; Thu, 18 Jul 2019 21:41:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 77437204FD for ; Thu, 18 Jul 2019 21:41:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="V5STNS/q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728032AbfGRVlv (ORCPT ); Thu, 18 Jul 2019 17:41:51 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:36337 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727685AbfGRVlu (ORCPT ); Thu, 18 Jul 2019 17:41:50 -0400 Received: by mail-pg1-f196.google.com with SMTP id l21so13472954pgm.3 for ; Thu, 18 Jul 2019 14:41:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=WXkPzSZf/fna3v9Du6552FbVJUMqyGEVvH1pVYvIMY4=; b=V5STNS/qoo+hoVZ84al1gz5fifOhZXi5TNLkAQyzXqvCHDez69Q42Gc1XWjzaNNbwG N7LT6lGx8NtDTUhplToKtR5wwYE6ctQpODx/wBZoo5gu5HBfYvoV6pcDfJt2GkeMitc3 NQse+pSPY+bAuwZMPQRQ1+RWkkLvdMU80lmc4= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=WXkPzSZf/fna3v9Du6552FbVJUMqyGEVvH1pVYvIMY4=; b=afHXiWrGl7KLDd2NuaBV6SMo1RdYSVpdND0HiQjxsb8qD3Tb2JZPth7lYIsBBQ+4wI 7DzwbIEw4vhuMKrKTo4t4Ivzmxn+TOcHpVDh05llOt1SJX/SM0X7eFlzcUoi1MC/Y58y 1kyD4TSDnpTBcQJikW13t5Uy1LvYPgl0iRktEi1sf7tRt8rsClhpIKDZH9l/nkCWOgvs gTjzt4JVtRgVKV+pZpqw+FEiP9YDCTEksfFxRNeTgLytDAEFx7KelZRukkmbLtZklIgH nbYBjm3yYMYZbJ5QNcd84OUMKhqfRsntpu55QAJsZD5AP31wMBMf4xXMdTi9mgbc2mqI 77Vg== X-Gm-Message-State: APjAAAU8/nGWXbOkmSXAVmiepJGuYvAk7KVfOoF0hUNvqhaxBPTLohS3 pjN0X7vYGIL6/bnRc8ghSNWyZg== X-Google-Smtp-Source: APXvYqyHVzz82WKLnz3eIxpxYsyXxPYr1dGo2TBVXXV3yFi26z+3ibdtZ3ZK/+C5B+QnidGKJlAWOQ== X-Received: by 2002:a63:f456:: with SMTP id p22mr23401451pgk.45.1563486109760; Thu, 18 Jul 2019 14:41:49 -0700 (PDT) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id e17sm16860239pgm.21.2019.07.18.14.41.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Jul 2019 14:41:49 -0700 (PDT) From: Matthias Kaehlcke To: Andrzej Hajda , Laurent Pinchart , David Airlie , Daniel Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Jose Abreu , Neil Armstrong , Douglas Anderson , Matthias Kaehlcke Subject: [PATCH] drm/bridge: dw-hdmi: Refuse DDC/CI transfers on the internal I2C controller Date: Thu, 18 Jul 2019 14:41:35 -0700 Message-Id: <20190718214135.79445-1-mka@chromium.org> X-Mailer: git-send-email 2.22.0.657.g960e92d24f-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The DDC/CI protocol involves sending a multi-byte request to the display via I2C, which is typically followed by a multi-byte response. The internal I2C controller only allows single byte reads/writes or reads of 8 sequential bytes, hence DDC/CI is not supported when the internal I2C controller is used. The I2C transfers complete without errors, however the data in the response is garbage. Abort transfers to/from slave address 0x37 (DDC) with -EOPNOTSUPP, to make it evident that the communication is failing. Signed-off-by: Matthias Kaehlcke --- drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index 045b1b13fd0e..e49402ebd56f 100644 --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c @@ -35,6 +35,7 @@ #include +#define DDC_I2C_ADDR 0x37 #define DDC_SEGMENT_ADDR 0x30 #define HDMI_EDID_LEN 512 @@ -322,6 +323,13 @@ static int dw_hdmi_i2c_xfer(struct i2c_adapter *adap, u8 addr = msgs[0].addr; int i, ret = 0; + if (addr == DDC_I2C_ADDR) + /* + * The internal I2C controller does not support the multi-byte + * read and write operations needed for DDC/VCP. + */ + return -EOPNOTSUPP; + dev_dbg(hdmi->dev, "xfer: num: %d, addr: %#x\n", num, addr); for (i = 0; i < num; i++) { -- 2.22.0.657.g960e92d24f-goog