From patchwork Wed Feb 1 02:38:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Huacai Chen X-Patchwork-Id: 13123663 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 C83CDC636CC for ; Wed, 1 Feb 2023 02:38:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230225AbjBACid (ORCPT ); Tue, 31 Jan 2023 21:38:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56854 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230177AbjBACic (ORCPT ); Tue, 31 Jan 2023 21:38:32 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15D104A208 for ; Tue, 31 Jan 2023 18:38:31 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B002460AFC for ; Wed, 1 Feb 2023 02:38:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ABC06C433D2; Wed, 1 Feb 2023 02:38:27 +0000 (UTC) From: Huacai Chen To: Bjorn Helgaas , Lorenzo Pieralisi , Rob Herring , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= Cc: linux-pci@vger.kernel.org, Jianmin Lv , Xuefeng Li , Huacai Chen , Jiaxun Yang , Huacai Chen Subject: [PATCH V3 1/2] PCI: Omit pci_disable_device() in pcie_port_device_remove() Date: Wed, 1 Feb 2023 10:38:02 +0800 Message-Id: <20230201023803.660469-2-chenhuacai@loongson.cn> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230201023803.660469-1-chenhuacai@loongson.cn> References: <20230201023803.660469-1-chenhuacai@loongson.cn> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org This patch has a long story. After cc27b735ad3a7557 ("PCI/portdrv: Turn off PCIe services during shutdown") we observe poweroff/reboot failures on systems with LS7A chipset. We found that if we remove "pci_command &= ~PCI_COMMAND_MASTER" in do_pci_disable_device(), it can work well. The hardware engineer says that the root cause is that CPU is still accessing PCIe devices while poweroff/reboot, and if we disable the Bus Master Bit at this time, the PCIe controller doesn't forward requests to downstream devices, and also does not send TIMEOUT to CPU, which causes CPU wait forever (hardware deadlock). To be clear, the sequence is like this: - CPU issues MMIO read to device below Root Port - LS7A Root Port fails to forward transaction to secondary bus because of LS7A Bus Master defect - CPU hangs waiting for response to MMIO read Then how is userspace able to use a device after the device is removed? To give more details, let's take the graphics driver (e.g. amdgpu) as an example. The userspace programs call printf() to display "shutting down xxx service" during shutdown/reboot, or the kernel calls printk() to display something during shutdown/reboot. These can happen at any time, even after we call pcie_port_device_remove() to disable the pcie port on the graphic card. The call stack is: printk() --> call_console_drivers() --> con->write() --> vt_console_print() --> fbcon_putcs() This scenario happens because userspace programs (or the kernel itself) don't know whether a device is 'usable', they just use it, at any time. This hardware behavior is a PCIe protocol violation (Bus Master should not be involved in CPU MMIO transactions), and it will be fixed in new revisions of hardware (add timeout mechanism for CPU read request, whether or not Bus Master bit is cleared). On some x86 platforms, radeon/amdgpu devices can cause similar problems [1][2]. Once before I add a quirk to solve the LS7A problem but looks ugly. After long time discussions, Bjorn Helgaas suggest simply remove the pci_disable_device() in pcie_port_device_remove() and this patch do it exactly. [1] https://bugs.freedesktop.org/show_bug.cgi?id=97980 [2] https://bugs.freedesktop.org/show_bug.cgi?id=98638 Signed-off-by: Huacai Chen --- drivers/pci/pcie/portdrv.c | 1 - 1 file changed, 1 deletion(-) diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c index 2cc2e60bcb39..9fe1fbca6476 100644 --- a/drivers/pci/pcie/portdrv.c +++ b/drivers/pci/pcie/portdrv.c @@ -501,7 +501,6 @@ static void pcie_port_device_remove(struct pci_dev *dev) { device_for_each_child(&dev->dev, NULL, remove_iter); pci_free_irq_vectors(dev); - pci_disable_device(dev); } /**