From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8ACCB15C158 for ; Sat, 23 Aug 2025 13:10:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755954604; cv=none; b=a4hUKPy/RGbGYyepGCCkS6LR4SMk3bBjXgGgtJOLU5CjWGQm+7FcJe883V/giWBv5KQA0yMvBeTIsiJhrCpbv5ibE8fAHlhrik7asuT45cqKVXURbO1brc9hU8n/wtj7rySUduSWEs6sRoZ1gn+I7njJuZJJLMfeKl21OzwPBoA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755954604; c=relaxed/simple; bh=ZCsK1iKGS9Z9QvTL6s7OqsTAVcTbw7cF2oclJSKw+AM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=hC5dgf+Sz1nBlTpzTajofxcODMfstOBR0jJwjvH0pl0Zf541/aoMfmN110scy+9YfH33kniZtso2PxCnK2VE4Ou0KlDnExDWGpwCsbw03a2Rvx4FrB0Oxr82B9j71T0GA0jwPvdPa5BD3lyEcC10b0v4m4BAPxJ2qYnjvvmoUbg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=blnCF6Bt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="blnCF6Bt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50CFEC4CEE7; Sat, 23 Aug 2025 13:10:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755954604; bh=ZCsK1iKGS9Z9QvTL6s7OqsTAVcTbw7cF2oclJSKw+AM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=blnCF6Bt4wxPmYVtQmBWEz4TmROnpSRR6FCtcllIiTzjr7Ft3tooPrzgKsBSuDstj dY4rGaac2lBIa+e59ZHU6n7ZTjPD0C+O1+8PUuHRNSuNWIV+CBVi3quO14OLNOFe9q bj8iAbPuSRhy3aOUiJ4J6dNRwkCXp+9n/iOXMYLXD3fYdimJiKydAziVM1DAvTK53W jY4ier0RJ8ji+FLYhBtHPLNgqJB0+WbdE3OflQiuXWqDzYK+gLe6NrDqyxEl29Xfn1 Yv3Aa/glHh9zTVYZMiFAuPolkuxqE5Wjmnvu431F2XeL3GESmKknd4kTXimWuPW1Sy jaGYt9hoLe7sw== From: Sasha Levin To: stable@vger.kernel.org Cc: Imre Deak , =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= , Jani Nikula , Jani Nikula , Sasha Levin Subject: [PATCH 6.6.y] drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS Date: Sat, 23 Aug 2025 09:10:01 -0400 Message-ID: <20250823131001.2113226-1-sashal@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025082149-disfigure-divinely-bc5c@gregkh> References: <2025082149-disfigure-divinely-bc5c@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Imre Deak [ Upstream commit a40c5d727b8111b5db424a1e43e14a1dcce1e77f ] 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 Syrjälä Cc: Jani Nikula Acked-by: Jani Nikula Signed-off-by: Imre Deak Link: https://lore.kernel.org/r/20250605082850.65136-2-imre.deak@intel.com Signed-off-by: Sasha Levin --- 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/display/drm_dp_helper.c index 851f0baf9460..772d8e662278 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -663,7 +663,7 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset, * monitor doesn't power down exactly after the throw away read. */ if (!aux->is_remote) { - ret = drm_dp_dpcd_probe(aux, DP_DPCD_REV); + ret = drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS); if (ret < 0) return ret; } -- 2.50.1