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 DECEB346FD4; Tue, 11 Nov 2025 01:15:30 +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=1762823731; cv=none; b=jW+yoaXXEMMjOmr1oTKJTm4ZXtLNZmYTUYK6eRp7molSNt9A++T/OJiEBh4yVPBhoc2QFgTrVPOIivyRSIlFVjWm5sg0pHixuRLHpghrc0S6Kpn3ESE/+NzyubplProkNAy+Fi1kIFi5eS8brbtnSPRi24+S0aiMlq3FIJkAXg8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762823731; c=relaxed/simple; bh=QM7ALa19JHZcOXaY2Blbs0J9ioHcTJ7VP6setV/4dgU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WeQg1dFoa8GwmyzYzYe4qkZUpcJr012KNlpCIU/WCOLPG1Cl1dBAdiF40mARCi1A0UXPKgArjhvmy/hVVNhcchRyTPw+1a2Cm9HaSOI1H8pC3937D5x1sdoeEFcXeA7Xd64casPyEoWmvaEQpEoEacdDRmtOyqOpX/sIFDToOIg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wILd5U1q; 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="wILd5U1q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D1FDC113D0; Tue, 11 Nov 2025 01:15:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762823730; bh=QM7ALa19JHZcOXaY2Blbs0J9ioHcTJ7VP6setV/4dgU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wILd5U1qdhV5QXZvEEvFyvqcTZt/lyiECTJM/+s6qwNAPVs9AlY+/4aMWeFuKsYeP GIfd3kqYm6UTVIR3utkwG/dyXlh/czqYbCLEnjmypOeB8LrTX/Xo4DP+ifp78dB75f yEfkO99vi73YU4KpGj5AOWRonZo6+xPlVnqkYtLQ= 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 6.12 309/565] drm/amd/display: Fix pbn_div Calculation Error Date: Tue, 11 Nov 2025 09:42:45 +0900 Message-ID: <20251111004533.836692948@linuxfoundation.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251111004526.816196597@linuxfoundation.org> References: <20251111004526.816196597@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 6.12-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 ffa0d7483ffc1..fd44d011ffd2d 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -7715,7 +7715,7 @@ 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 92158009cfa73..a2a70c1e9afdc 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 @@ -816,13 +816,20 @@ 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