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b=KyeYXcF7CKUQypplR3ttje+dCZo0UwNOWE6vSDmZDPVMw6Z5YqYBzCpbUrXWj2Pwl+9K2JMl8XHYOA88PKqhB6ovLAERRAwMpRxMuu9+L4ll4EF1i+E+fOx6vzcAUP+OFEeOV/C0cunNFyrlgU3rS1PpXuWKlqt7VNiQyQQS0+I= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DM6PR12MB4877.namprd12.prod.outlook.com (2603:10b6:5:1bb::24) by MN2PR12MB4440.namprd12.prod.outlook.com (2603:10b6:208:26e::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7784.19; Wed, 24 Jul 2024 20:06:01 +0000 Received: from DM6PR12MB4877.namprd12.prod.outlook.com ([fe80::92ad:22ff:bff2:d475]) by DM6PR12MB4877.namprd12.prod.outlook.com ([fe80::92ad:22ff:bff2:d475%4]) with mapi id 15.20.7784.020; Wed, 24 Jul 2024 20:06:01 +0000 Message-ID: <28b953c3-ef66-4bd2-a024-ec860399ffbf@amd.com> Date: Wed, 24 Jul 2024 15:05:59 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 03/10] PCI/TPH: Add pci=notph to prevent use of TPH To: Bjorn Helgaas Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, netdev@vger.kernel.org, Jonathan.Cameron@huawei.com, corbet@lwn.net, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, alex.williamson@redhat.com, gospo@broadcom.com, michael.chan@broadcom.com, ajit.khaparde@broadcom.com, somnath.kotur@broadcom.com, andrew.gospodarek@broadcom.com, manoj.panicker2@amd.com, Eric.VanTassell@amd.com, vadim.fedorenko@linux.dev, horms@kernel.org, bagasdotme@gmail.com, bhelgaas@google.com References: <20240723224102.GA779599@bhelgaas> Content-Language: en-US From: Wei Huang In-Reply-To: <20240723224102.GA779599@bhelgaas> Content-Type: text/plain; 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What kind of issues? Crash? Data corruption? Poor > performance? Not crash or functionality errors. Usually it is QoS related because of resource competition. AMD has > >> Provide a kernel option, with related helper functions, to completely >> prevent TPH from being enabled. > > Also would be nice to have a hint about the difference between "notph" > and "nostmode". Maybe that goes in the "nostmode" patch? I'm not > super clear on all the differences here. I can combine them. Here is the combination and it meaning based on TPH Control Register values: Requestor Enable | ST Mode | Meaning --------------------------------------------------------------- 00 | xx | TPH disabled (i.e. notph) 01 | 00 | TPH enabled, NO ST Mode (i.e. nostmode) 01 or 11 | 01 | Interrupt Vector mode 01 or 11 | 10 | Device specific mode If you have any other thoughts on how to approach these modes, please let me know. > >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -4655,6 +4655,7 @@ >> nomio [S390] Do not use MIO instructions. >> norid [S390] ignore the RID field and force use of >> one PCI domain per PCI function >> + notph [PCIE] Do not use PCIe TPH > > Expand acronym here since there's no helpful context. Can also > include "(TPH)" if that's useful. > >> @@ -322,8 +323,12 @@ static long local_pci_probe(void *_ddi) >> pm_runtime_get_sync(dev); >> pci_dev->driver = pci_drv; >> rc = pci_drv->probe(pci_dev, ddi->id); >> - if (!rc) >> + if (!rc) { >> + if (pci_tph_disabled()) >> + pcie_tph_disable(pci_dev); > > I'm not really a fan of cluttering probe() like this. Can't we > disable it in pcie_tph_init() so all devices start off with TPH > disabled, and then check pci_tph_disabled() in whatever interface > drivers use to enable TPH? > >> +bool pci_tph_disabled(void) >> +{ >> + return pcie_tph_disabled; >> +} >> +EXPORT_SYMBOL_GPL(pci_tph_disabled); > > Other related interfaces use "pcie" prefix; I think this should match. > > Do drivers need this? Would be nice not to export it unless they do. > > Bjorn