From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 696172EFD80; Wed, 3 Sep 2025 22:55:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756940129; cv=none; b=JlgLxYUk9DhaPD/Bv3JqA65w3mNy72eWJ6y0utf02wiysUPiXTg7LvWeqf5sGRQ1hknamwrzmD16Wak2f+oADDJYzvSLlkfunaKOS+NEWOBBYmuU+y6YpFt5eqmP31w+ZCWD6kIEqt8lVKSAcdFdfu2nL/0dmcsbuIoFCrlA/Tw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756940129; c=relaxed/simple; bh=1VgGtMZsWvs80zyeZmeX0N1kSokjzXOz9E4Nb9E9dD8=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=Maiiw0XdHRz54JOJifMLEOc2areYNOCoJuAD4rCF9ycQ3E7xGjzAavmG6yNvU/+t4aTT7w+wZrNNIc+mQU7xDWCMV8kqYykX0I0QCbqylHVWYL7lZ3x20YBiNUqOSJLPWL3gccs/xXYmBruVYy6YH2FeGiaB6es6WSusVo4CP88= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lXnHhCdj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lXnHhCdj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B2FD3C4CEE7; Wed, 3 Sep 2025 22:55:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756940128; bh=1VgGtMZsWvs80zyeZmeX0N1kSokjzXOz9E4Nb9E9dD8=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=lXnHhCdjC99sj9uGG9oV9sG4kb9KCqUAT4Ys+KBfjrMN9j2nv1062Z10Cc0bw8ncn Gw43AHBHHydaTnX/Z2mgF5PSwEuwuRptsY9a/D7QcFym6D76UrbYEROrV3WhJST/OO wUEE3J9XFZ1rRErS5mmfJf1yNb6zATqF45fxbEl5Oquy49lbqvzlkxl3yO7UwWBwK3 UHbv4lNgom2seevc25qo591uc9K7s8dYJYojsKTu9l9aIKcWvC0UYOiwmEVno4s5jc F/veSmKPMcH/mkmzn07HNkcmrlzDxcu1Z8jYmsOfgUCx4b5mrjSy3+j3xsxphgIDH2 8rCDRufj1ZYug== Date: Wed, 3 Sep 2025 17:55:27 -0500 From: Bjorn Helgaas To: Manivannan Sadhasivam Cc: "David E. Box" , rafael@kernel.org, bhelgaas@google.com, vicamo.yang@canonical.com, kenny@panix.com, ilpo.jarvinen@linux.intel.com, nirmal.patel@linux.intel.com, linux-pm@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 1/2] PCI/ASPM: Add host-bridge API to override default ASPM/CLKPM link state Message-ID: <20250903225527.GA1236657@bhelgaas> Precedence: bulk X-Mailing-List: linux-pm@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: <2fo64esrc5v5vj46iff2ptgcthaeahwicuzug46popwqrryfsi@yt62sqsnv4e3> On Sun, Aug 31, 2025 at 06:28:53PM +0530, Manivannan Sadhasivam wrote: > On Thu, Aug 28, 2025 at 03:43:45PM GMT, Bjorn Helgaas wrote: > > On Mon, Aug 25, 2025 at 01:35:22PM -0700, David E. Box wrote: > > > Synthetic PCIe hierarchies, such as those created by Intel VMD, are not > > > enumerated by firmware and do not receive BIOS-provided ASPM or CLKPM > > > defaults. Devices in such domains may therefore run without the intended > > > power management. > > > > > > Add a host-bridge mechanism that lets controller drivers supply their own > > > defaults. A new aspm_default_link_state field in struct pci_host_bridge is > > > set via pci_host_set_default_pcie_link_state(). During link initialization, > > > if this field is non-zero, ASPM and CLKPM defaults come from it instead of > > > BIOS. > > > > > > This enables drivers like VMD to align link power management with platform > > > expectations and avoids embedding controller-specific quirks in ASPM core > > > logic. > > > > I think this kind of sidesteps the real issue. Drivers for host > > controllers or PCI devices should tell us about *broken* things, but > > not about things advertised by the hardware and available for use. > > > > The only documented policy controls I'm aware of for ASPM are: > > > > - FADT "PCIe ASPM Controls" bit ("if set, OS must not enable ASPM > > control on this platform") > > > > - _OSC negotiation for control of the PCIe Capability (OS is only > > allowed to write PCI_EXP_LNKCTL if platform has granted control to > > the OS) > > > > I think what we *should* be doing is enabling ASPM when it's > > advertised, subject to those platform policy controls and user choices > > like CONFIG_PCIEASPM_PERFORMANCE/POWERSAVE/etc and sysfs attributes. > > > > So basically I think link->aspm_default should be PCIE_LINK_STATE_ALL > > without drivers doing anything at all. Maybe we have to carve out > > exceptions, e.g., "VMD hierarchies are exempt from _OSC," or "devices > > on x86 systems before 2026 can't enable more ASPM than BIOS did," or > > whatever. Is there any baby step we can make in that direction? > > I'm not sure about the ACPI world, but for devicetree platforms, > BIOS or the bootloader won't configure ASPM for the devices > (mostly). So the baby step would be to set PCIE_LINK_STATE_ALL for > all devicetree platforms :) Yes. How likely would this be to break something? Before doing that, I think we need to add some logging, at least at pci_dbg(), of what is already enabled and what we change, so we have some kind of hint when things do break.