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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E248DC433F5 for ; Mon, 22 Nov 2021 17:53:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239542AbhKVR5B (ORCPT ); Mon, 22 Nov 2021 12:57:01 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:4146 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239540AbhKVR5B (ORCPT ); Mon, 22 Nov 2021 12:57:01 -0500 Received: from fraeml735-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4HyZd26gYpz6GDMt; Tue, 23 Nov 2021 01:53:26 +0800 (CST) Received: from lhreml710-chm.china.huawei.com (10.201.108.61) by fraeml735-chm.china.huawei.com (10.206.15.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Mon, 22 Nov 2021 18:53:51 +0100 Received: from localhost (10.202.226.41) by lhreml710-chm.china.huawei.com (10.201.108.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Mon, 22 Nov 2021 17:53:50 +0000 Date: Mon, 22 Nov 2021 17:53:49 +0000 From: Jonathan Cameron To: Ben Widawsky CC: , , "Alison Schofield" , Dan Williams , Ira Weiny , Vishal Verma Subject: Re: [PATCH 04/23] cxl/pci: Implement Interface Ready Timeout Message-ID: <20211122175349.00007ced@Huawei.com> In-Reply-To: <20211122171731.2hzsmspdhgw2wyqi@intel.com> References: <20211120000250.1663391-1-ben.widawsky@intel.com> <20211120000250.1663391-5-ben.widawsky@intel.com> <20211122150227.00000020@Huawei.com> <20211122171731.2hzsmspdhgw2wyqi@intel.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.29; i686-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.41] X-ClientProxiedBy: lhreml737-chm.china.huawei.com (10.201.108.187) To lhreml710-chm.china.huawei.com (10.201.108.61) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On Mon, 22 Nov 2021 09:17:31 -0800 Ben Widawsky wrote: > On 21-11-22 15:02:27, Jonathan Cameron wrote: > > On Fri, 19 Nov 2021 16:02:31 -0800 > > Ben Widawsky wrote: > > > > > The original driver implementation used the doorbell timeout for the > > > Mailbox Interface Ready bit to piggy back off of, since the latter > > > doesn't have a defined timeout. This functionality, introduced in > > > 8adaf747c9f0 ("cxl/mem: Find device capabilities"), can now be improved > > > since a timeout has been defined with an ECN to the 2.0 spec. > > > > > > While devices implemented prior to the ECN could have an arbitrarily > > > long wait and still be within spec, the max ECN value (256s) is chosen > > > as the default for all devices. All vendors in the consortium agreed to > > > this amount and so it is reasonable to assume no devices made will > > > exceed this amount. > > > > Optimistic :) > > > > Reasonable to assume is certainly not the same as "in reality". I can soften > this wording. > > > > > > > Signed-off-by: Ben Widawsky > > > --- > > > This patch did not exist in RFCv2 > > > --- > > > drivers/cxl/pci.c | 29 +++++++++++++++++++++++++++++ > > > 1 file changed, 29 insertions(+) > > > > > > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c > > > index 6c8d09fb3a17..2cef9fec8599 100644 > > > --- a/drivers/cxl/pci.c > > > +++ b/drivers/cxl/pci.c > > > @@ -2,6 +2,7 @@ > > > /* Copyright(c) 2020 Intel Corporation. All rights reserved. */ > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -298,6 +299,34 @@ static int cxl_pci_mbox_send(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *c > > > static int cxl_pci_setup_mailbox(struct cxl_dev_state *cxlds) > > > { > > > const int cap = readl(cxlds->regs.mbox + CXLDEV_MBOX_CAPS_OFFSET); > > > + unsigned long timeout; > > > + u64 md_status; > > > + int rc; > > > + > > > + /* > > > + * CXL 2.0 ECN "Add Mailbox Ready Time" defines a capability field to > > > + * dictate how long to wait for the mailbox to become ready. For > > > + * simplicity, and to handle devices that might have been implemented > > > > I'm not keen on the 'for simplicity' argument here. If the device is advertising > > a lower value, then that is what we should use. It's fine to wait the max time > > if nothing is specified. It'll cost us a few lines of code at most unless > > I am missing something... > > > > Jonathan > > > > Let me pose it a different way, if a device advertises 1s, but for whatever > takes 4s to come up, should we penalize it over the device advertising 256s? Yes, because it is buggy. A compliance test should have failed on this anyway. > The > way this field is defined in the spec would [IMHO] lead vendors to simply put > the max field in there to game the driver, so why not start off with just > insisting they don't? Given reading this value and getting a big number gives the implication that the device is meant to be really slow to initialize, I'd expect that to push vendors a little in the directly of putting realistic values in). Maybe we should print the value in the log to make them look silly ;) Jonathan > > > > + * prior to the ECN, wait the max amount of time no matter what the > > > + * device says. > > > + */ > > > + timeout = jiffies + 256 * HZ; > > > + > > > + rc = check_device_status(cxlds); > > > + if (rc) > > > + return rc; > > > + > > > + do { > > > + md_status = readq(cxlds->regs.memdev + CXLMDEV_STATUS_OFFSET); > > > + if (md_status & CXLMDEV_MBOX_IF_READY) > > > + break; > > > + if (msleep_interruptible(100)) > > > + break; > > > + } while (!time_after(jiffies, timeout)); > > > + > > > + /* It's assumed that once the interface is ready, it will remain ready. */ > > > + if (!(md_status & CXLMDEV_MBOX_IF_READY)) > > > + return -EIO; > > > > > > cxlds->mbox_send = cxl_pci_mbox_send; > > > cxlds->payload_size = > >