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 483F31366; Mon, 3 Jun 2024 17:19:23 +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=1717435165; cv=none; b=d3YA+eOQuDCQ2a3Kg4EjCZeV0DGMF2QFJRLtdmFEumhS4Wdys8xXPE0ppTym/WfiNZjubL/K1yHm80JfsEl+FZ8Ol0nE0jSf1ojSVFWTrQnNwPc3QUhO/0xu1YfgM5GU4btl5VMWOYta0x4tjdJbuOoysnw6S8WnxACzbk+p9Eo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717435165; c=relaxed/simple; bh=o+oMkH1I/WbYDZBa3qcXo8pOhVZODTPPaT5jeLn7qIU=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=XfUIR+Wknw80lfl4SkipQrYQBEgaDUMnMwTNzPJBmFhG42xr5s92WImA9/5Z3q/ILqc02uGEAJhudIUEkhi0dL+IYTH4fYb5nw2XjbeXTc2CzCgqN2wHglQrtOrXnsB7B+bSu5ghmlIeyaUaSoK/wyAB6O3vmUjlSXppShj4xco= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hhwFWKSS; 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="hhwFWKSS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6583AC2BD10; Mon, 3 Jun 2024 17:19:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1717435163; bh=o+oMkH1I/WbYDZBa3qcXo8pOhVZODTPPaT5jeLn7qIU=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=hhwFWKSSd4vV2hTYoNib68G4aE53A9hjm/qJTppKcaTVXqZ3K4F8FnfKdI32g6R3a luQD8Z1RYHtLwXs/M4NQm1fJAZTRopSgdO0Qd1pfmpGSIjWtjcPMnzrzxaKgxM9H33 CxTXWuL1hlBkHGtPKRVAcKxUyGElF8oR2vHTLhHFWTJ20+qfZJwH52g8tNJs1qQkOX d56VBM/qpQ/5gtIL6YY7XK+4+BS34uQx8Rw3B2QRMGeObdl9V/+S8TC/qp9mJY6MtV CdUAFpYDItJ8i6wpM/BKPyNsSLCDzPpJ38jiex4vFTOBdxidxBBuNCg4W4RS3deaJt NFjppavpkC5Jg== Date: Mon, 3 Jun 2024 12:19:21 -0500 From: Bjorn Helgaas To: Robin Murphy Cc: Frank Li , Richard Zhu , Lucas Stach , Lorenzo Pieralisi , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Rob Herring , Bjorn Helgaas , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , Philipp Zabel , Liam Girdwood , Mark Brown , Manivannan Sadhasivam , Krzysztof Kozlowski , Conor Dooley , linux-pci@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, devicetree@vger.kernel.org, Will Deacon , Joerg Roedel , Jason Gunthorpe , Alyssa Rosenzweig , Marc Zyngier Subject: Re: [PATCH v5 08/12] PCI: imx6: Config look up table(LUT) to support MSI ITS and IOMMU for i.MX95 Message-ID: <20240603171921.GA685838@bhelgaas> Precedence: bulk X-Mailing-List: devicetree@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: <974f1d23-aba8-432e-85b5-0e4b1c2005e7@arm.com> On Fri, May 31, 2024 at 03:58:49PM +0100, Robin Murphy wrote: > On 2024-05-31 12:08 am, Bjorn Helgaas wrote: > > [+cc IOMMU and pcie-apple.c folks for comment] > > > > On Tue, May 28, 2024 at 03:39:21PM -0400, Frank Li wrote: > > > For the i.MX95, configuration of a LUT is necessary to convert Bus Device > > > Function (BDF) to stream IDs, which are utilized by both IOMMU and ITS. > > > This involves examining the msi-map and smmu-map to ensure consistent > > > mapping of PCI BDF to the same stream IDs. Subsequently, LUT-related > > > registers are configured. In the absence of an msi-map, the built-in MSI > > > controller is utilized as a fallback. > > > > > > Additionally, register a PCI bus notifier to trigger imx_pcie_add_device() > > > upon the appearance of a new PCI device and when the bus is an iMX6 PCI > > > controller. This function configures the correct LUT based on Device Tree > > > Settings (DTS). > > > > This scheme is pretty similar to apple_pcie_bus_notifier(). If we > > have to do this, I wish it were *more* similar, i.e., copy the > > function names, bitmap tracking, code structure, etc. > > > > I don't really know how stream IDs work, but I assume they are used on > > most or all arm64 platforms, so I'm a little surprised that of all the > > PCI host drivers used on arm64, only pcie-apple.c and pci-imx6.c need > > this notifier. > > This is one of those things that's mostly at the mercy of the PCIe root > complex implementation. Typically the SMMU StreamID and/or GIC ITS DeviceID > is derived directly from the PCI RID, sometimes with additional high-order > bits hard-wired to disambiguate PCI segments. I believe this RID-translation > LUT is a particular feature of the the Synopsys IP - I know there's also one > on the NXP Layerscape platforms, but on those it's programmed by the > bootloader, which also generates the appropriate "msi-map" and "iommu-map" > properties to match. Ideally that's what i.MX should do as well, but hey. Maybe this RID-translation is a feature of i.MX, not of Synopsys? I see that the LUT CSR accesses use IMX95_* definitions. > If it's really necessary to do this programming from Linux, then there's > still no point in it being dynamic - the mappings cannot ever change, since > the rest of the kernel believes that what the DT said at boot time was > already a property of the hardware. It would be a lot more logical, and > likely simpler, for the driver to just read the relevant map property and > program the entire LUT to match, all in one go at controller probe time. > Rather like what's already commonly done with the parsing of "dma-ranges" to > program address-translation LUTs for inbound windows. > > Plus that would also give a chance of safely dealing with bad DTs specifying > invalid ID mappings (by refusing to probe at all). As it is, returning an > error from a child's BUS_NOTIFY_ADD_DEVICE does nothing except prevent any > further notifiers from running at that point - the device will still be > added, allowed to bind a driver, and able to start sending DMA/MSI traffic > without the controller being correctly programmed, which at best won't work > and at worst may break the whole system. Frank, could the imx LUT be programmed once at boot-time instead of at device-add time? I'm guessing maybe not because apparently there is a risk of running out of LUT entries? It sounds like the consequences of running out of LUT entries are catastrophic, e.g., memory corruption from mis-directed DMA? If that's possible, I think we need to figure out how to prevent the device from being used, not just dev_warn() about it. Bjorn