From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bmailout2.hostsharing.net (bmailout2.hostsharing.net [83.223.78.240]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C40A9189BA3; Thu, 29 Aug 2024 09:32:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=83.223.78.240 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724923980; cv=none; b=oBfs/ZpnACQAJwqmAIExg1IksnvjYw0G1Dr3KP0Dm81Gb/IUTJcnYWznZnSNcviMLpQazUaog/DFXe2u0K4yDhPizNTtoY5Rpuz69nOhoXbqliymfu0t3CUaFoa9RPGtpnipjvEfEuU9Zg36NLdYRae/7GSdS/7IABbXWMaiVuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724923980; c=relaxed/simple; bh=yGCID0GCiA9pXFJg0fO8tvyOnGozjM+tId2ELiGSJsw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ic5en6ndqL4xYsJtIsE1PxM1VBludjpODUDnZqCY2NyXdxbIDfp44c9rYqJ0AZdBPaDJhjC68Jcj9QNz36js0fTf+MZv3uLq3LTlrIxWt5JTEG+zoQ7b/ggxfqUUUyOW3WlM8Fo70zcz1uS/Xixs3ciaDWZpszSq/3+XQl5W/oI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de; spf=none smtp.mailfrom=h08.hostsharing.net; arc=none smtp.client-ip=83.223.78.240 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=h08.hostsharing.net Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by bmailout2.hostsharing.net (Postfix) with ESMTPS id 8E4AF28036B3A; Thu, 29 Aug 2024 11:32:47 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 676935B1ED; Thu, 29 Aug 2024 11:32:47 +0200 (CEST) Date: Thu, 29 Aug 2024 11:32:47 +0200 From: Lukas Wunner To: Esther Shimanovich Cc: Bjorn Helgaas , Rajat Jain , "Rafael J. Wysocki" , Mario Limonciello , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , iommu@lists.linux.dev, Mika Westerberg , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] PCI: Detect and trust built-in Thunderbolt chips Message-ID: References: <20240823-trust-tbt-fix-v4-1-c6f1e3bdd9be@chromium.org> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Aug 28, 2024 at 05:15:24PM -0400, Esther Shimanovich wrote: > On Sun, Aug 25, 2024 at 10:49???AM Lukas Wunner wrote: > > On Fri, Aug 23, 2024 at 04:53:16PM +0000, Esther Shimanovich wrote: > > > --- a/drivers/pci/probe.c > > > +++ b/drivers/pci/probe.c > > > +static bool pcie_has_usb4_host_interface(struct pci_dev *pdev) > > > +{ > > > + struct fwnode_handle *fwnode; > > > + > > > + /* > > > + * For USB4, the tunneled PCIe root or downstream ports are marked > > > + * with the "usb4-host-interface" ACPI property, so we look for > > > + * that first. This should cover most cases. > > > + */ > > > + fwnode = fwnode_find_reference(dev_fwnode(&pdev->dev), > > > + "usb4-host-interface", 0); > > > > This is all ACPI only, so it should either be #ifdef'ed to CONFIG_ACPI > > or moved to drivers/pci/pci-acpi.c. > > > > Alternatively, it could be moved to arch/x86/pci/ because ACPI can also > > be enabled on arm64 or riscv but the issue seems to only affect x86. > > Thanks for the feedback! Adding an #ifdef to CONFIG_ACPI seems more > straightforward, but I do like the idea of not having unnecessary code > run on non-x86 systems. > > I'd appreciate some guidance here. How would I move a portion of a > function into a completely different location in the kernel src? > Could you show me an example? One way to do this would be to move pcie_is_tunneled(), pcie_has_usb4_host_interface() and pcie_switch_directly_under() to arch/x86/pci/acpi.c. Rename pcie_is_tunneled() to arch_pci_dev_is_removable() and remove the "static" declaration specifier from that function. Add a function declaration for arch_pci_dev_is_removable() to include/linux/pci.h. Add a __weak arch_pci_dev_is_removable() function which just returns false in drivers/pci/probe.c right above pci_set_removable(). And that's it. See pcibios_device_add() for an example. That's one way to do it. It ensures that the code is only compiled on x86 and only if CONFIG_ACPI=y. Basically the linker picks the arch_pci_dev_is_removable() in arch/x86/pci/acpi.c, or the empty __weak function of the same name on !x86 or if CONFIG_ACPI=n. An alternative approach would involve using an empty static inline. I think the difference is that an empty static inline is optimized away by the compiler, whereas the empty __weak function is not optimized away by the compiler, but may be optimized away by the linker if CONFIG_LTO=y. For the static inline it's basically the same but you omit the __weak arch_pci_dev_is_removable() in drivers/pci/probe.c and instead constrain the function declaration in include/linux/pci.h to: #if defined(CONFIG_X86) && defined(CONFIG_ACPI) ...and the #else branch would contain the empty static inline which just returns false. See pci_mmcfg_early_init() for an example. Maybe the empty static inline is better because then the entire "if (arch_pci_dev_is_removable(...))" clause can be optimized away without reliance on CONFIG_LTO=y. I hope I haven't confused you completely. Thanks, Lukas