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 A55A223D287 for ; Sat, 23 Aug 2025 12:56:28 +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=1755953788; cv=none; b=Zz999LAx0qGDMUH41q6lbFrT+pIuMCl68fXK4OZgLkHlNpb8Zj2yGnifCWxT57m7fuzJyb8zoWNrQg26nBAX3NzR231iUVLbL8taDOe027BcU5P7nGmRv5J5BnBeC5upvstnW/8b+Rr07hvwuGUo50eqgMu/nctKusK3J9rg7vc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755953788; c=relaxed/simple; bh=mDfi+vGDYy1phkvkQZOno74ILGCGwVxkGNZnwuUkHU0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=IOwuN/OOixHN4MDUa6XjCT2Sonlxj+oL28kvyLm9m+QYLKyE7aih+3YWrdhKR6v0gtvX2VIYWtfYDfwBnQxbfvPdoZJ3MRK5YPE1oeLQtZA25QVom1SPjKgw6z1gtVT3gW6aU/HKvgdPDJ8vA4tCMfnZ2QZRj6rmmfmnVOtwBPM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gs9mkBWK; 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="gs9mkBWK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79C81C4CEF4; Sat, 23 Aug 2025 12:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755953788; bh=mDfi+vGDYy1phkvkQZOno74ILGCGwVxkGNZnwuUkHU0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gs9mkBWKFOyN9KzCDG41wQ/JJu3FN2K+dN/3pFnmLCzf91/uC720oGIeLbv15RHkX 48W82Hs3nt+UMcZZsVXpLA13NdWsKOhFT15NkdyWUomcFrDmJhL7XmKgfqax4oKQvF sAL4cFTEw3Zxjb/mCOoko6UeaZJlfMGNRfnfJEg7GTx2VH7WL1+BMsyOfxP0+JcCcF IyLveh/RhIqb29xYqSHHsfjulqqepOkGAWW5tAJ8txx8VutDcNSkBLR6LBAGvWYD4C hrTAPaND8TyTmYxV2LK2coVAbPEtVyvgwEsy0isqD5JEBxsOzWnqah0dVwXujzK2S8 qCkD9Qj0zQ2dw== 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 6.16.y] drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS Date: Sat, 23 Aug 2025 08:56:25 -0400 Message-ID: <20250823125625.2103160-1-sashal@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025082148-refutable-outmatch-8a67@gregkh> References: <2025082148-refutable-outmatch-8a67@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 [ DP_TRAINING_PATTERN_SET => DP_LANE0_1_STATUS ] 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 ea78c6c8ca7a..dc622c78db9d 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, 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_TRAINING_PATTERN_SET); + ret = drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS); if (ret < 0) return ret; } -- 2.50.1