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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham 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 2F27AC282C4 for ; Tue, 12 Feb 2019 17:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0895B20842 for ; Tue, 12 Feb 2019 17:49:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729289AbfBLRtp (ORCPT ); Tue, 12 Feb 2019 12:49:45 -0500 Received: from bmailout2.hostsharing.net ([83.223.90.240]:37209 "EHLO bmailout2.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728027AbfBLRtp (ORCPT ); Tue, 12 Feb 2019 12:49:45 -0500 Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "COMODO RSA Domain Validation Secure Server CA" (not verified)) by bmailout2.hostsharing.net (Postfix) with ESMTPS id 57F622800B1DF; Tue, 12 Feb 2019 18:49:43 +0100 (CET) Received: by h08.hostsharing.net (Postfix, from userid 100393) id EC961160E1D; Tue, 12 Feb 2019 18:49:42 +0100 (CET) Date: Tue, 12 Feb 2019 18:49:42 +0100 From: Lukas Wunner To: Mika Westerberg Cc: linux-kernel@vger.kernel.org, Michael Jamet , Yehezkel Bernat , Andreas Noever , Andy Shevchenko Subject: Re: [PATCH v2 16/28] thunderbolt: Discover preboot PCIe paths the boot firmware established Message-ID: <20190212174942.if2ene44f5m5mern@wunner.de> References: <20190206131738.43696-1-mika.westerberg@linux.intel.com> <20190206131738.43696-17-mika.westerberg@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190206131738.43696-17-mika.westerberg@linux.intel.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 06, 2019 at 04:17:26PM +0300, Mika Westerberg wrote: > /* dword 0 */ > hop.next_hop = path->hops[i].next_hop_index; > hop.out_port = path->hops[i].out_port->port; > - /* TODO: figure out why these are good values */ > - hop.initial_credits = (i == path->path_length - 1) ? 16 : 7; > + hop.initial_credits = path->hops[i].initial_credits; > hop.unknown1 = 0; > hop.enable = 1; [...] > @@ -78,6 +78,74 @@ static void tb_pci_init_path(struct tb_path *path) > path->weight = 1; > path->drop_packages = 0; > path->nfc_credits = 0; > + path->hops[0].initial_credits = 7; > + path->hops[1].initial_credits = 16; I guess Andreas' algorithm (the last hop in the path is assigned 16 and all the ones before are assigned 7) was reverse-engineered from Apple's driver. The fact that this algorithm works for paths of arbitrary length could indicate that Apple indeed does establish tunnels between non-adjacent switches. Also, why are these good values? (You've deleted the comment.) Thanks, Lukas