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 C86132C178D; Wed, 25 Feb 2026 01:45:54 +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=1771983954; cv=none; b=Zsvs15PldqA2gWFb4zcHvOvNv9Nza5ccPazIizmFGjX48hdr+sWxP8JQYbKLac5kmpA4Bi7T2zEax/m9sbzvrYqtsi2tPXCEetshuC9kYa+RoU0v1Ko/IfHcxa8s77KoYwsKYWGDfOkbdvnsVbZj7ly/0EEePt8U4jtATptsz1I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771983954; c=relaxed/simple; bh=Em5vjysqGvSd61996NmG9063HzhpFyV2u/M7jIGcIJc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=L0l2t0mb5r85jdWpx/AOiMWFv+LNCvMrD0LnspuK4xFyldU2ho9FuQz4YnyFkcO9nqMn2MGD1vrpc43rjcCs6fKSuTTw4OE6VMjRWmO/A7cawBsfLBWzNM2qfmvqfCq94d31pDdfUR1VeMbxnEodDmta91tfMOptxlNyb4i7OPU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dUSmmX2g; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dUSmmX2g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71E27C19423; Wed, 25 Feb 2026 01:45:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1771983954; bh=Em5vjysqGvSd61996NmG9063HzhpFyV2u/M7jIGcIJc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dUSmmX2g/xgcD20fKg/gPQmye8oXcJFuH7tJteKkjFw4dV9U12YclQGHSV7Di9ebN aGTDmzDZAsXdB9bvbkZdZjAS0wgyFeo+YqrJU0J/lZAOjcNA1XWD74aGlKjKMFhNCE DfTl+R9FNst3+F9wBCWk/AXixLiZRwVqRe/wRhh0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, kernel test robot , Konrad Dybcio , Nathan Chancellor , Dmitry Baryshkov , Sasha Levin Subject: [PATCH 6.18 213/641] drm/msm/dp: Avoid division by zero in msm_dp_ctrl_config_msa() Date: Tue, 24 Feb 2026 17:18:59 -0800 Message-ID: <20260225012354.102203693@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012348.915798704@linuxfoundation.org> References: <20260225012348.915798704@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nathan Chancellor [ Upstream commit f185076da44c774241a16a82a7773ece3c1c607b ] An (admittedly problematic) optimization change in LLVM 20 [1] turns known division by zero into the equivalent of __builtin_unreachable(), which invokes undefined behavior if it is encountered in a control flow graph, destroying code generation. When compile testing for x86_64, objtool flags an instance of this optimization triggering in msm_dp_ctrl_config_msa(), inlined into msm_dp_ctrl_on_stream(): drivers/gpu/drm/msm/msm.o: warning: objtool: msm_dp_ctrl_on_stream(): unexpected end of section .text.msm_dp_ctrl_on_stream The zero division happens if the else branch in the first if statement in msm_dp_ctrl_config_msa() is taken because pixel_div is initialized to zero and it is not possible for LLVM to eliminate the else branch since rate is still not known after inlining into msm_dp_ctrl_on_stream(). Transform the if statements into a switch statement with a default case with the existing error print and an early return to avoid the invalid division. Add a comment to note this helps the compiler, even though the case is known to be unreachable. With this, pixel_dev's default zero initialization can be dropped, as it is dead with this change. Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support") Link: https://github.com/llvm/llvm-project/commit/37932643abab699e8bb1def08b7eb4eae7ff1448 [1] Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202601081959.9UVJEOfP-lkp@intel.com/ Suggested-by: Konrad Dybcio Signed-off-by: Nathan Chancellor Reviewed-by: Dmitry Baryshkov Patchwork: https://patchwork.freedesktop.org/patch/698355/ Link: https://lore.kernel.org/r/20260113-drm-msm-dp_ctrl-avoid-zero-div-v2-1-f1aa67bf6e8e@kernel.org Signed-off-by: Dmitry Baryshkov Signed-off-by: Sasha Levin --- drivers/gpu/drm/msm/dp/dp_ctrl.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c index c42fd2c17a328..38ed4de8313e3 100644 --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c @@ -2395,20 +2395,32 @@ static void msm_dp_ctrl_config_msa(struct msm_dp_ctrl_private *ctrl, bool is_ycbcr_420) { u32 pixel_m, pixel_n; - u32 mvid, nvid, pixel_div = 0, dispcc_input_rate; + u32 mvid, nvid, pixel_div, dispcc_input_rate; u32 const nvid_fixed = DP_LINK_CONSTANT_N_VALUE; u32 const link_rate_hbr2 = 540000; u32 const link_rate_hbr3 = 810000; unsigned long den, num; - if (rate == link_rate_hbr3) + switch (rate) { + case link_rate_hbr3: pixel_div = 6; - else if (rate == 162000 || rate == 270000) - pixel_div = 2; - else if (rate == link_rate_hbr2) + break; + case link_rate_hbr2: pixel_div = 4; - else + break; + case 162000: + case 270000: + pixel_div = 2; + break; + default: + /* + * This cannot be reached but the compiler is not able to know + * that statically so return early to avoid a possibly invalid + * division. + */ DRM_ERROR("Invalid pixel mux divider\n"); + return; + } dispcc_input_rate = (rate * 10) / pixel_div; -- 2.51.0