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 B638526AC3; Tue, 11 Nov 2025 01:23:01 +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=1762824181; cv=none; b=pBTFex8zEWSsxgzse5f6S8otDR+wyAmuY9WfzpnKVQOjmN+KzoHSyLwpYgRVAtDZXoDXKH/qjC6M3g/t2QT17TGNOtEk93i1/3h3j1P2Sbuf1AkHJ61cr5xpWB0ipHS795iXt1eP4Ys9+N7bnJTJs8meS9Vfajz4FBFzT+n0qSs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762824181; c=relaxed/simple; bh=OzdyECXGHv10qXSQ/xA/NcxIXVK7XIG/0eAwlLsTYHU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mzF++Da7pyYxzY3502j41ayACK/iSImebrsPw2LXQn+xVPd/kW0Kvy/rgPO7vNsJmR9OlFr3DSp34WsQRAKTis80xEmuZLyENcsGiWW6T8xzMNY3m3at6WfKgiq8OvUIcylOeRaxtlO+HjZGvKwrnx1Va4Z1dSixZNnbtOlD+5I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gNPfaqwL; 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="gNPfaqwL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12B77C116D0; Tue, 11 Nov 2025 01:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762824181; bh=OzdyECXGHv10qXSQ/xA/NcxIXVK7XIG/0eAwlLsTYHU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gNPfaqwL6lDA2zjWeWVp0wyd81mrJ/7m7gqtVGVEr0LAAWgO4N0Suvv1ViLe+pe2d rCvio7aCy9/scQfx2OiesnQ7J7eIlSDM94pkaBU5WS8F+cKld5qGnwc07upFFD7AQO oPeH9iOwfnFEZ9Gtid8N8NyzbsVQK0LZq4Yeakig= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Aurabindo Pillai , Fangzhi Zuo , Wayne Lin , Dan Wheeler , Alex Deucher , Sasha Levin Subject: [PATCH 6.17 457/849] drm/amd/display: Fix pbn_div Calculation Error Date: Tue, 11 Nov 2025 09:40:27 +0900 Message-ID: <20251111004547.478230959@linuxfoundation.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251111004536.460310036@linuxfoundation.org> References: <20251111004536.460310036@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Fangzhi Zuo [ Upstream commit 12cdfb61b32a7be581ec5932e0b6a482cb098204 ] [Why] dm_mst_get_pbn_divider() returns value integer coming from the cast from fixed point, but the casted integer will then be used in dfixed_const to be multiplied by 4096. The cast from fixed point to integer causes the calculation error becomes bigger when multiplied by 4096. That makes the calculated pbn_div value becomes smaller than it should be, which leads to the req_slot number becomes bigger. Such error is getting reflected in 8k30 timing, where the correct and incorrect calculated req_slot 62.9 Vs 63.1. That makes the wrong calculation failed to light up 8k30 after a dock under HBR3 x 4. [How] Restore the accuracy by keeping the fraction part calculated for the left shift operation. Reviewed-by: Aurabindo Pillai Signed-off-by: Fangzhi Zuo Signed-off-by: Wayne Lin Tested-by: Dan Wheeler Signed-off-by: Alex Deucher Signed-off-by: Sasha Levin --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 13 ++++++++++--- .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h | 2 +- 3 files changed, 12 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index aca57cc815514..afe3a8279c3a9 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -7974,7 +7974,7 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder, if (IS_ERR(mst_state)) return PTR_ERR(mst_state); - mst_state->pbn_div.full = dfixed_const(dm_mst_get_pbn_divider(aconnector->mst_root->dc_link)); + mst_state->pbn_div.full = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link); if (!state->duplicated) { int max_bpc = conn_state->max_requested_bpc; diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c index 77a9d2c7d3185..5412bf046062c 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c @@ -822,13 +822,20 @@ void amdgpu_dm_initialize_dp_connector(struct amdgpu_display_manager *dm, drm_connector_attach_dp_subconnector_property(&aconnector->base); } -int dm_mst_get_pbn_divider(struct dc_link *link) +uint32_t dm_mst_get_pbn_divider(struct dc_link *link) { + uint32_t pbn_div_x100; + uint64_t dividend, divisor; + if (!link) return 0; - return dc_link_bandwidth_kbps(link, - dc_link_get_link_cap(link)) / (8 * 1000 * 54); + dividend = (uint64_t)dc_link_bandwidth_kbps(link, dc_link_get_link_cap(link)) * 100; + divisor = 8 * 1000 * 54; + + pbn_div_x100 = div64_u64(dividend, divisor); + + return dfixed_const(pbn_div_x100) / 100; } struct dsc_mst_fairness_params { diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h index 600d6e2210111..179f622492dbf 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h @@ -59,7 +59,7 @@ enum mst_msg_ready_type { struct amdgpu_display_manager; struct amdgpu_dm_connector; -int dm_mst_get_pbn_divider(struct dc_link *link); +uint32_t dm_mst_get_pbn_divider(struct dc_link *link); void amdgpu_dm_initialize_dp_connector(struct amdgpu_display_manager *dm, struct amdgpu_dm_connector *aconnector, -- 2.51.0