From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA33DC433DF for ; Tue, 23 Jun 2020 20:48:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9495E217A0 for ; Tue, 23 Jun 2020 20:48:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592945303; bh=yKwDromzh+5kxVNfUQzkvziM7JwRsWVesvwqkeHcJcU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=hXh4UpC3NjtOa2yvr6Qna8Z5N7yA9kTEWJahLsdVO4FxgDyj/no2svcnSK6jrvAgP 7qtnFlSKlBFw9Zkuu/D0gc61ww85CBpr1G1DtvX+nHIFWWQtZfITk5aB6UM64IIShY VQEwTSytAgot4ea5o7MI643LKMEKjrd4fRWeK1jI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392934AbgFWUsV (ORCPT ); Tue, 23 Jun 2020 16:48:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:47214 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392640AbgFWUsQ (ORCPT ); Tue, 23 Jun 2020 16:48:16 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7944221548; Tue, 23 Jun 2020 20:48:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592945296; bh=yKwDromzh+5kxVNfUQzkvziM7JwRsWVesvwqkeHcJcU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vfcjkfeWAunHCUqZD5sRboL7rm9jqAkJpg0sznNnMcDGIcfJiiMNf50C4zV3kRgy1 MZ0l1JQn6bOyxL1sBng9iD2xda5hWxuC7PE1Z8YvNJXr7biZ9Hm39EeAngJtCbkA3z Kn2gLtjuLItiQB6gkcnv1YM6BojtRuAInIm8r4vs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Lyude Paul , Sean Paul , Sasha Levin Subject: [PATCH 4.14 116/136] drm/dp_mst: Increase ACT retry timeout to 3s Date: Tue, 23 Jun 2020 21:59:32 +0200 Message-Id: <20200623195309.528055212@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200623195303.601828702@linuxfoundation.org> References: <20200623195303.601828702@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lyude Paul [ Upstream commit 873a95e0d59ac06901ae261dda0b7165ffd002b8 ] Currently we only poll for an ACT up to 30 times, with a busy-wait delay of 100µs between each attempt - giving us a timeout of 2900µs. While this might seem sensible, it would appear that in certain scenarios it can take dramatically longer then that for us to receive an ACT. On one of the EVGA MST hubs that I have available, I observed said hub sometimes taking longer then a second before signalling the ACT. These delays mostly seem to occur when previous sideband messages we've sent are NAKd by the hub, however it wouldn't be particularly surprising if it's possible to reproduce times like this simply by introducing branch devices with large LCTs since payload allocations have to take effect on every downstream device up to the payload's target. So, instead of just retrying 30 times we poll for the ACT for up to 3ms, and additionally use usleep_range() to avoid a very long and rude busy-wait. Note that the previous retry count of 30 appears to have been arbitrarily chosen, as I can't find any mention of a recommended timeout or retry count for ACTs in the DisplayPort 2.0 specification. This also goes for the range we were previously using for udelay(), although I suspect that was just copied from the recommended delay for link training on SST devices. Changes since v1: * Use readx_poll_timeout() instead of open-coding timeout loop - Sean Paul Changes since v2: * Increase poll interval to 200us - Sean Paul * Print status in hex when we timeout waiting for ACT - Sean Paul Signed-off-by: Lyude Paul Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)") Cc: Sean Paul Cc: # v3.17+ Reviewed-by: Sean Paul Link: https://patchwork.freedesktop.org/patch/msgid/20200406221253.1307209-4-lyude@redhat.com Signed-off-by: Sasha Levin --- drivers/gpu/drm/drm_dp_mst_topology.c | 54 ++++++++++++++++----------- 1 file changed, 32 insertions(+), 22 deletions(-) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index df5d853f96eed..e52381c9d04ee 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -29,6 +29,7 @@ #include #include #include +#include #include #include @@ -2751,6 +2752,17 @@ static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr, return ret; } +static int do_get_act_status(struct drm_dp_aux *aux) +{ + int ret; + u8 status; + + ret = drm_dp_dpcd_readb(aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status); + if (ret < 0) + return ret; + + return status; +} /** * drm_dp_check_act_status() - Check ACT handled status. @@ -2760,30 +2772,28 @@ static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr, */ int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr) { - int count = 0, ret; - u8 status; - - do { - ret = drm_dp_dpcd_readb(mgr->aux, - DP_PAYLOAD_TABLE_UPDATE_STATUS, - &status); - if (ret < 0) { - DRM_DEBUG_KMS("failed to read payload table status %d\n", - ret); - return ret; - } - - if (status & DP_PAYLOAD_ACT_HANDLED) - break; - count++; - udelay(100); - } while (count < 30); - - if (!(status & DP_PAYLOAD_ACT_HANDLED)) { - DRM_DEBUG_KMS("failed to get ACT bit %d after %d retries\n", - status, count); + /* + * There doesn't seem to be any recommended retry count or timeout in + * the MST specification. Since some hubs have been observed to take + * over 1 second to update their payload allocations under certain + * conditions, we use a rather large timeout value. + */ + const int timeout_ms = 3000; + int ret, status; + + ret = readx_poll_timeout(do_get_act_status, mgr->aux, status, + status & DP_PAYLOAD_ACT_HANDLED || status < 0, + 200, timeout_ms * USEC_PER_MSEC); + if (ret < 0 && status >= 0) { + DRM_DEBUG_KMS("Failed to get ACT after %dms, last status: %02x\n", + timeout_ms, status); return -EINVAL; + } else if (status < 0) { + DRM_DEBUG_KMS("Failed to read payload table status: %d\n", + status); + return status; } + return 0; } EXPORT_SYMBOL(drm_dp_check_act_status); -- 2.25.1