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 D5C99389455; Fri, 17 Jul 2026 11:33:23 +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=1784288005; cv=none; b=YEcY8H1jX9adAFUA2G4AJQlSTBzxoLgQXt55lXSuzSHoaJ1yP5ONRzdme/51dSmKNQyIgZIn58KRyoykTIVVpYJrZSsWiOPT1ryuFrNRZUaUPwCDKe/9XzYJ+fUqqdwQMUsT8HjWF2zJct29jKe2qlnPzsAs4wo4SoEgoYXVHQg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784288005; c=relaxed/simple; bh=6BETA+wKcoLv8Jpz6mIx2oFg5zQncmW6ai6+tT1x6Sc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FG8s5podI9JRUFkSRFgFAVEEmV6wGXuj3Z/2Mk08vYYw9eUCfGo/tlR5QZESXmWaRSbTtvq7u8hN8jF2E5i/ORbSd4HEMa7bNdQCeiQJLCS/bRCqju4kmO1NcKgjpfoKp+3p0YxVaFIBkdHH4G8FTUwBtoIp2usSSdeO5G94sgU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iq42tPbO; 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="iq42tPbO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 546FB1F00A3A; Fri, 17 Jul 2026 11:33:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784288003; bh=eIjS9piUmE57cYRXDTfna1Rukyb5JMZSPthrMyRy+dI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=iq42tPbOoZtO6nh+GKjVtUHfeIfHZK1bmON1BBNXij/itmb7LzRjjBIJY8GKdmjGP 1JUZugohNu6nNjBQ3aato7NA94Hnl1Fngrs2kPfUVZvhy5/RcJ/q+HaW0sxbVW5SWH sb60zNG2UeU5cBwkdVxIJrxNQrz4rO88mC/vlk/zLOnm+uZ0JY+NoeqUn2ugpYXilx vw5TXrxruuDeqeUtA8m/+nR4R2eIyXaEMGkeji5naXwDFnkHgRtqN0TrY05ZeiAg3l P1wpDK2SXbmf9z22nXHLmBPsM6BXwmw/RJpng9h+X66d5J+c9Eil+Rs5SFgny6uA1C 1/oEcd/H4t+0g== Date: Fri, 17 Jul 2026 12:33:17 +0100 From: Will Deacon To: Ryan Roberts Cc: Greg Kroah-Hartman , Arnd Bergmann , Catalin Marinas , Mark Rutland , Jean-Philippe Brucker , Oded Gabbay , Jonathan Corbet , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org, maz@kernel.org, oupton@kernel.org, hch@infradead.org, jgg@nvidia.com Subject: Re: [RFC PATCH v1 0/8] Arm Core Local Accelerator Driver Message-ID: References: <20260717104759.123203-1-ryan.roberts@arm.com> Precedence: bulk X-Mailing-List: linux-doc@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: <20260717104759.123203-1-ryan.roberts@arm.com> Hi Ryan, I haven't bothered to look at the code (looks like Sashiko is having fun with that), but I'm going to jump at this bit: On Fri, Jul 17, 2026 at 11:47:44AM +0100, Ryan Roberts wrote: > * User space availability: The kernel driver exposes the capabilities of the > hardware to user space. Arm plans to open source a user space driver, but does > not yet have any committed date. I'd like to understand if the availability of > this component will be a prerequisite for upstream acceptance of the kernel > driver; either way, I'm hoping we can at least progress with some discussion > in its absence. >From my perspective, I'm not particularly interested in having code in the upstream kernel tree that we can't meaningfully exercise or benefit from. I also think that the incentive for Arm to open source the user-space driver practically disappears if we merge the kernel part first. So, at the moment, this just looks like a burden to me, especially as it appears to create a brand new, device-specific UAPI for what is ostensibly a form of SVA - something which the community is actively working on already. Relatedly, is there a spec and/or fastmodel/qemu (sorry...) support for this? > I'm deliberately constraining the scope to bare-metal support for now. > Virtualization is something we are considering (and have prototyped), but plan > to post a separate RFC for that as follow-up, once we have agreement on > direction for the bare-metal driver. I'd actually like to see what the virtualisation part looks like first because doing it as a bolt-on later feels like the wrong approach. The structure you have at the moment is remarkably clean, given the architectural/CPU interactions (this thing even apparently builds as a module, nice!), but I'm unsure how far you can push the separation once you need to start hacking at KVM. Maybe the MMU notifiers are enough, but I can't tell. Will