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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B86E0C5B555 for ; Wed, 4 Jun 2025 09:53:31 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6E2D810E734; Wed, 4 Jun 2025 09:53:30 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="WK+T8KJp"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.12]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4F92910E71D; Wed, 4 Jun 2025 09:53:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1749030809; x=1780566809; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version:content-transfer-encoding; bh=KbRUAm4RyvmymdxAzoWXejNZHiSqmFjxI5CD3AiI5b4=; b=WK+T8KJp0IDlRIu/kUF/ha4LmdpggKl9IfIkQUD3QRFYkOid8BXGhUKX h1lVB82pAQVoUTfMzX4nKq7OoOWAgxwoYpYpPOQTRH7BEWb1amb45iPHT prdt6cGjlazPyP/echjkG5HE1K5TusVUaWWg6757rhfBIlcOMvYzpTUiu JHYw88kgMO2QyPRmIPf/pxoPmXNcedCOh/v3TEJLh5pn3yEmxibahWwiE +OuECK3wp+SX6kEKlWV+z2QfpkJYkWzdpFfWMXb1ZfZ4SpxNxDU/gyMJN tHhSD1pCbDqwziO5eNqjktLBTF2Y8VGtT124CefHtrRSWmJLlbOLM63Rh w==; X-CSE-ConnectionGUID: fYn4GXb/RyKe1Exur71XXQ== X-CSE-MsgGUID: Oisf9oO3R5C9I9b6sLS2Aw== X-IronPort-AV: E=McAfee;i="6700,10204,11453"; a="62492962" X-IronPort-AV: E=Sophos;i="6.16,208,1744095600"; d="scan'208";a="62492962" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2025 02:53:28 -0700 X-CSE-ConnectionGUID: vk172RNDQn+6wgHiZ0INXw== X-CSE-MsgGUID: +wIxuW3sQ9CoKCQBdDM77g== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,208,1744095600"; d="scan'208";a="168312276" Received: from abityuts-desk.ger.corp.intel.com (HELO localhost) ([10.245.245.101]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2025 02:53:26 -0700 From: Jani Nikula To: Imre Deak , intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org, Ville =?utf-8?B?U3lyasOkbMOk?= Subject: Re: [PATCH 1/4] drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS In-Reply-To: <20250603121543.17842-2-imre.deak@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20250603121543.17842-1-imre.deak@intel.com> <20250603121543.17842-2-imre.deak@intel.com> Date: Wed, 04 Jun 2025 12:53:23 +0300 Message-ID: <892023ee348a6bcad3fd553cafe6ff650974fa3f@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" On Tue, 03 Jun 2025, Imre Deak wrote: > Reading DPCD registers has side-effects in general. In particular > accessing registers outside of the link training register range > (0x102-0x106, 0x202-0x207, 0x200c-0x200f, 0x2216) is explicitly > forbidden by the DP v2.1 Standard, see > > 3.6.5.1 DPTX AUX Transaction Handling Mandates > 3.6.7.4 128b/132b DP Link Layer LTTPR Link Training Mandates > > Based on my tests, accessing the DPCD_REV register during the link > training of an UHBR TBT DP tunnel sink leads to link training failures. > > Solve the above by using the DP_LANE0_1_STATUS (0x202) register for the > DPCD register access quirk. > > Cc: > Cc: Ville Syrj=C3=A4l=C3=A4 > Cc: Jani Nikula > Signed-off-by: Imre Deak Acked-by: Jani Nikula > --- > drivers/gpu/drm/display/drm_dp_helper.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/di= splay/drm_dp_helper.c > index f2a6559a27100..dc622c78db9d4 100644 > --- a/drivers/gpu/drm/display/drm_dp_helper.c > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > @@ -725,7 +725,7 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsi= gned int offset, > * monitor doesn't power down exactly after the throw away read. > */ > if (!aux->is_remote) { > - ret =3D drm_dp_dpcd_probe(aux, DP_DPCD_REV); > + ret =3D drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS); > if (ret < 0) > return ret; > } --=20 Jani Nikula, Intel