From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-128.mta1.migadu.com [95.215.58.128]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B33753A88A for ; Wed, 23 Sep 2026 16:43:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.128 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790181804; cv=none; b=fcbWEcQQki5pr1szv/Ihc0rsTlcyI7WwcEFwjyzDpy8xRVjhqQ5oKDtzxxl16fQd9WGA0j51wUme6w2HasZ0haUXMr2r+UqSN2+UIW0RvFWoLIdUWTpBDrqF3NtMCyqSwlG++Yb+V29t8VJHvHn1atvBGrU9wWpZS6UEk/Plwck= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790181804; c=relaxed/simple; bh=z5PVQJxayxGeNQifTwwvxx8fDx6857gHo9VSiCt+4cY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MPak4J8AGaEqcf9jvlUgnz6HL7zCmeWWjlMNnaHX3o9znTVt5uyuwYh6U2xEtf9jMdBwNsDHH0tR+KXJEYDstqlHPMVhqX+dbbfEmJrDzjpoT8W1XMNh/NN26E5xGjCId4VCHsGR4IqXH2KOJqxgNlJqip9WVH7LMIc+7mW68eI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=OvHxP9xf; arc=none smtp.client-ip=95.215.58.128 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="OvHxP9xf" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=z5PVQJxayxGeNQifTwwvxx8fDx6857gHo9VSiCt+4cY=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790181793; v=1; x=1790786593; b=OvHxP9xf1DVCchKRxQ/+HFpSC1KOAKXV+Qx3KmfU258EQ4IKCfjd+xF9Wt4DZsdiGhyeOMOy nQ10EGSXmBzWVgNUNZUVL4REk6tuU40hESCOvxDXiw8WhbfD8fpstdZJoqjp4BJ37kyWh4qABl5 qH6rO8Rwk2s+1NEg5YHO5XGs= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 64eb0ac43514703d; Wed, 23 Sep 2026 16:43:13 +0000 X-Mizu-Trace-ID: 64eb0ac43514703d X-Migadu-Flow: FLOW_OUT Message-ID: <12839ca0-cb1d-41da-9e48-bbec59ebf230@linux.dev> Date: Wed, 23 Sep 2026 18:43:12 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] fpga: region: Add support for FPGA region variants To: Krzysztof Kozlowski , Xu Yilun Cc: Moritz Fischer , Xu Yilun , Tom Rix , linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org, Rob Herring , Saravana Kannan , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org References: <417b510f-0f6d-4695-97f5-3fc19b9377b9@linux.dev> <9d4af487-69a7-4a0d-9335-35c3a057de54@linux.dev> <4dbdb52e-1b28-432e-a3a7-ad9c44f17d27@linux.dev> <8848432d-45b0-4efe-adf3-adfb64fe0899@linux.dev> <11b1a792-f8b1-4fce-8a7a-8352149febcf@linux.dev> <2adefc6f-328c-4683-8cba-091d9f3425ab@linux.dev> <1857df9a-8952-426e-988b-cd05d45a04cc@kernel.org> Content-Language: en-US From: Marco Pagani In-Reply-To: <1857df9a-8952-426e-988b-cd05d45a04cc@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 23/09/2026 17:09, Krzysztof Kozlowski wrote: > On 23/09/2026 16:30, Marco Pagani wrote: >> >> >> On 18/09/2026 19:36, Xu Yilun wrote: >>> On Fri, Sep 18, 2026 at 05:07:07PM +0200, Marco Pagani wrote: >>>> >>>> Hi Yilun, >>>> >>>> Is it okay with you if I CC the DT people to ask for an opinion? >>> >>> Of course. It's good to know in which case could a DTO be applied. >>> >>> But to be clear, I think that only affects how we accept and apply the >>> image-DTO pair. For now, I basically don't want a varient selection >>> interface. >> >> >> Hello Rob, Saravana, Krzysztof, Conor, >> >> I'm CC-ing you on this thread as OF/DT maintainers to kindly ask >> for your input on this debate we are having about how to implement >> userspace FPGA reconfiguration, an important feature currently >> lacking in mainline kernel. >> >> https://lore.kernel.org/all/20260608164247.1998417-1-marco.pagani@linux.dev >> >> To recap: modern FPGAs allow portions of the fabric to be reconfigured >> at runtime to dynamically swap soft IPs. Usually, these IPs are >> connected through a non-discoverable on-chip bus like AMBA AXI. >> From a kernel perspective, this means the FPGA device configuration >> image (bitstream) must be paired with a DT fragment that describes >> the new topology. >> >> In this thread, we are essentially debating between two approaches for >> implementing FPGA userspace reconfiguration at runtime: >> >> - Statically defined Variants (this RFC): Userspace can change FPGA >> configuration by selecting from a pre-validated set of variants >> (DT fragments) baked into the base DT. > > I don't know what DT fragments are, maybe you meant overlays? But they > are not baked into the base DT. > > There are no bindings here and no DT maintainers were CCed on this RFC, > so I really do not get how this patch can enable something like that. > > Linked URL shows some undocumented ABI, so obviously this would be a no > go. And RFC prefix does not justify undocumented ABI. At least one > without clear explanation in the cover letter, why is this RFC and why > it cannot be merged/reviewed. Sorry, I couldn't have imagined that missing ABI documentation in a "proof of concept" RFC would be so detrimental while asking for a high-level opinion. > >> >> - Runtime DTOs (Nava's RFC): Userspace can change FPGA configuration >> by loading DTOs that are validated at runtime. > > If runtime overlays were working, this looks suitable to the problem of > runtime change of the hardware. This also fits hot-pluggable hardware > problem, which Bootlin is working on. Glad to know the problem is already being solved. Thanks, Marco