From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 01EAE3A1B5; Wed, 24 Jun 2026 10:16:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782296184; cv=none; b=X3shp1SeZLKIW2z5bDkJ5PrceNLHGDnG28pkfbhhcZPWzx+XpOQoMORKYEYdeIX/BltgyL2m75VHmdkkFpVdM8MsDLTfCpGuvRs7yKNsafWD2R3apWSfFSIza26jRC1+2eekUi+aJ22UI2w2awCWkGHVK3mvtn+O1q98DUhMeRA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782296184; c=relaxed/simple; bh=j8UuGJIyvmP9xPOBDHNazf2wL6EEJUXPI+1z20bDwzo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=axgmRD0on8Q4MfGk+C7MxP41nlDQVR1wwr9qGyYPCNkgQ3r146cyT/xizKWrlrYSTvU6SOisMoZ0YTRMlf67H//CJRTaj4ibhvQJmn2Ybs8013ss0z7WzSgHFXqFvRtZF+lSauPJTolif6deuvY20lxqkoRiOwOShdH4hZGTZUk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B7jkjlYZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="B7jkjlYZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E40A01F000E9; Wed, 24 Jun 2026 10:16:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782296182; bh=52jh7JTXdS/PPkJ7pb4Ja7p6UQgePUeTTMff1Q4ccjs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=B7jkjlYZ31/W0IDZ2EtI1vgQv9ahx1MLABtvG4b4p1XZw+gxnAbWFJhSe6ju0jeDC TVx9CIKOe539vQBeytJTy57Xrhwolfbw6ZnS1wUW8lIU1VQVpk8kc+/ol14ScwRlkE MB01+Pl4RaUD3yrlDYjH1bIhK4Uaqd/ls54Jikb76FZfCyLnJ+WZTWkLzu/f3yAUFf w9xltKBPugpEvpgFLV9DQrqNwaxh78enlT+8DxdMRaPAbPd5i9x2kUxOGwVdQi4TAG 5ouWnmASlTQXWdwHKgrqZSm++cObqa1rGrK0I6AwucAud+gRkSAb3LU6+egiwVWIBK uxP4Q7UJ1GfDg== Message-ID: Date: Wed, 24 Jun 2026 12:16:15 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] dma-iommu: Introduce API to reserve IOVA regions for dynamically created devices To: Jason Gunthorpe Cc: Vishnu Reddy , Rob Herring , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org, Vikash Garodia , Robin Murphy , joro@8bytes.org, will@kernel.org, m.szyprowski@samsung.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, dikshita.agarwal@oss.qualcomm.com References: <20260119054936.3350128-1-busanna.reddy@oss.qualcomm.com> <20260612172649.GM1066031@ziepe.ca> <20260615125257.GS1066031@ziepe.ca> <20260617194038.GC231643@ziepe.ca> <20260618151745.GD231643@ziepe.ca> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 18/06/2026 17:17, Jason Gunthorpe wrote: > On Thu, Jun 18, 2026 at 01:57:40PM +0200, Krzysztof Kozlowski wrote: > >> Same with interrupt-map. > >> There are PCIe controller nodes which have interrupt-map and no >> interrupts property ever uses them. > > PCIe is quite a different situation because we expect Linux to > dynamically create the child nodes based on PCIe discovery, and the > various maps are all searched based on the PCI BDF based on HW > properties of real discovered child devices. > > Here they created "vpu_bus" and create a bunch of devices for some > reason, but they are all hard coded in the driver. It is not a dynamic > discovery, and it is not creating "real" child devices. Yes, true. > >> Because DT person - me - told that creating child device nodes just to >> configure iommus is abuse of DT. There are no child devices in terms of >> hardware or firmware. The iommu ranges here are no real hardware. > > That doesn't seem to be what Vishnu is saying. Review the earlier two > emails explaining what the HW issue is here: > > https://lore.kernel.org/all/bb59f07e-ca7e-f012-6a4b-0a148350b69c@oss.qualcomm.com/ > https://lore.kernel.org/all/cb37e7cc-4fb0-4c24-8f89-f6f9eb08a107@oss.qualcomm.com/ > > The VPU HW diagram with different IOVA requirements for different > stream IDs seems to be an entirely HW based thing: "each context bank > enforces a different IOVA range" > > The original patches just created a 0 based IOVA space per stream and > justified that by increasing the IOVA address space (make sense). The > email above now says some of the streams only function with a limited > range of IOVA because the HW uses the IOVA itself to select the > streams (insane!) > > IOW this entire device is completely mis-designed if it is going to > easially support the Linux DMA API :( That's all HW mess, which is > motivating hacks to try to make the Linux DMA API do something usable > by this device. > > Anyhow.. > > In Linux if you use DT iommus the SW sets things up so every stream > shares the same translation. If your driver/device doesn't like that > there is no SW way to opt out of sharing. I think that is the first > core issue that VPU was struggling with. > > If you have one "device" then I would argue the DT should describe all > its streams using iommus in the normal way. The introduction of > iommu-map for VPU is only being done because that is a convenient hack > to allow Linux to unbundle the streams. It would be much harder to > unbunble the streams directly from the DT iommus property, but that > would probably be the cleanest, software agnostic, DT modeling. > > So, if we are going to do a hack in DT to accomodate Linux, I argue to > choose explicit child devices so VPU does not need to create a special > bus, call of_dma_configue, or hack in new DMA API things that only it > will ever use. Then the explicit children can properly describe how > the HW decodes IOVA into each streams in the DT (which sounds very > much like a HW property to me) so that Linux produces IOVA that the HW > mangling properly routes to the expected stream. > > Then the VPU driver just has to assemble itself from many struct > devices, which I admit is also a troublesome task. > >> However, said all this, since I pushed folks to come with the iommu-map >> approach, I will revoke my disagreement to child device nodes in DT, if >> you really believe that is the approach. IOW, I will agree to device >> nodes in DT representing fake hardware-children, just for the sake of >> Linux driver model limitations. > > I would wait for Robin, he knows this better, but I belive this was > broadly his point in the original email.. Thanks Jason for context and detailed arguments. Robin did not chime in yet, but from what I understood the DT-child-node approach will be the way we should go here. I accept above point of view and I am fine with this, thus Vishnu and Vikash - please go ahead with DT-child-node solution we had some time ago. Best regards, Krzysztof