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 E8554155C97 for ; Sat, 23 Aug 2025 13:55:22 +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=1755957323; cv=none; b=uWajzpA35QycozOXGnXW4TdRMTgVa/NROzsMI6KeE5XRgvnVmLcEUopX5a7hO1BWNlqdFvx/Ka7Js7VRfuRf72qKf1szNKpbDsnM0pykyzPbNVJTa7FDg4TyF68kVFGxtGpBLVzM8lP/IkzRVjadEV7Nh1zmmOCvjG4xWrmHDlw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755957323; c=relaxed/simple; bh=uApoFVoXlP5AoUFpKrckGcNzb+S5XLADtHbpPP2xcF4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=GCqVVcODxSGGRDWezDEax5Pl7LIu754OkrC0eVDZzOsksVY9Lge973RwCADLzKhdbfJxOKiktT8r4JwK7tsrkB0sKl/JAmywJEvv49rc4zjvIgoF6CJU5RWyHtaudOPDzKUB7zDoxqkjbSl7W3NtoQoUwU5ICle54Knqkjvc9/g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B60UAVLT; 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="B60UAVLT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14195C4CEE7; Sat, 23 Aug 2025 13:55:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755957322; bh=uApoFVoXlP5AoUFpKrckGcNzb+S5XLADtHbpPP2xcF4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=B60UAVLTCWofPIUIRUhUIHvq/9yNOUALuPb6WAl1G/jnt0icXy9FD3km8DOpa4kAt KDMrgsqBi/KAjuc/1tWJ2E+8YdyyAMprAXNQLImPuAUaZPmaKHtC9CmoOlBRnmJCzY Mh+DVQkWvxIonm3xLOi48xBBirDduLIJm2naYe3O/WcU93XcdS/AUh0X8ySbxHbyGq EvzSP9bBBa3y5GNE1op9V9/J0/qvJxJ+JhrO9w6oARhTwgoyixYVs7F3HiNM4Gqrfp SewP2ILzBxFfyzFq5/xS269geObTgTQXXWFpDHpHQotAf2VWuV37A0sC3l/JMyBf3d E1dXyJPyTmvUQ== 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 5.15.y] drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS Date: Sat, 23 Aug 2025 09:55:20 -0400 Message-ID: <20250823135520.2154797-1-sashal@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025082151-chase-quilt-9ad4@gregkh> References: <2025082151-chase-quilt-9ad4@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 [ call to drm_dp_dpcd_access() instead of drm_dp_dpcd_probe() ] Signed-off-by: Sasha Levin --- drivers/gpu/drm/drm_dp_helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index b8815e7f5832..e830e461edd1 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -336,7 +336,7 @@ 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_access(aux, DP_AUX_NATIVE_READ, DP_DPCD_REV, + ret = drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, DP_LANE0_1_STATUS, buffer, 1); if (ret != 1) goto out; -- 2.50.1