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 4BD98363096; Wed, 11 Mar 2026 16:27:12 +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=1773246432; cv=none; b=LZyBnRBDPk4mbwPyZvyzGEHMKKimy51UydH7C6lEX+5x4txKFtwykbBuCprCcMAa+81tfvF+OCZhpRkZobgXsiJcsFQxmViRbTRfwhkLx0MTkgw8urvclcD8nH/XgjyS8jKPC+gSSo/CHXXt361xi2r6n95kFo7IjjedBeNRhnI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773246432; c=relaxed/simple; bh=wbWDlFakEbaP7591lyejSUYCXT2xlc/64V7XYHmWuqQ=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=Hw9sQnw4hlrb6AF1ISCAxS1Pw/tlpiprWZ4TZyBFjPS5Nk49KHMnNqBlTHyfjhJA2ukFltxQwO7uL3a+48+zoKck/0ZwvNSGR0ebsoZJGfny/zTg7xKsQddzbtlJw527MmaHgeEYiZ0LMggDORGRJXWwDVg7Mt8ZJVJAJYmqPzw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ASIZ/Kp2; 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="ASIZ/Kp2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55531C4CEF7; Wed, 11 Mar 2026 16:27:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773246432; bh=wbWDlFakEbaP7591lyejSUYCXT2xlc/64V7XYHmWuqQ=; h=Date:Subject:To:References:From:In-Reply-To:From; b=ASIZ/Kp2NgSiDRESZ92d/joGF3k6OwHDLB9xsawC2GeE1ewKmpNDTf9opNLLJV0U7 Wedkn73ctsIpKiY4jdu4GBiWwvkhLANydq97J91qdG/6xV0I41pauMwx+0XAagKJcY ZDvRDdF9L6N2KRbxSz/SIbbkdp5j4bZLt/SgCpZQUdGa4X3cGPHVY0sjQ2VSjEROvY fIh1gVfesg2xw3sy1eOFWL88hsS51hRoq/jSa6cNmYdGgSWBG++zF38YblgC3A1iUv +erV0gFl5pCpRA2rS+E7gdMaf2E2xdWBUyqAF4N6d4qsfQcFnhRxISvfPW2A1EUf59 ltw4adfiK3mCQ== Message-ID: Date: Wed, 11 Mar 2026 17:27:08 +0100 Precedence: bulk X-Mailing-List: linux-spi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: SPI loopback tests To: Francesco Dolcini , Mark Brown , Rob Herring , Conor Dooley , linux-spi@vger.kernel.org, devicetree@vger.kernel.org, Max Krummenacher References: <20260310133254.GA51497@francesco-nb> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/03/2026 14:32, Francesco Dolcini wrote: > Hello all, > > I am writing to you SPI, test and DT people with reference to some need > we see in our testing infrastructure. > > On our embedded boards we regularly (on mailine linux, on Linux LTS, and > on multiple hardware) run SPI tests, using a loopback connection (SPI > MISO/MOSI are connected together). The HW provide just some pin header > and there is no actual SPI slave device connected. > > So far to test this we had some out-of-tree DT overlay abusing the spidev > compatible, however we'd like to move away from this approach and have a > solution that is 100% in mainline. > > Manually unbinding/binding the driver in userspace does not seems as an > option, because there is no device node. > > One option that I could think of would be to add a new compatible that > to describe this single wire loopback connection (something like > `linux,spi-miso-mosi-loopback`) that would bind to the spidev driver. Or the modern board file way: a module which in initcall creates several SW nodes and instantiates the spidev. You still would need to insmode it of course, but that way no DT would be directly involved. > > I am aware that you all DT maintainers shared in a pretty clear way your > view on the abuse of the spidev multiple times. > > What would you be your advice to handle the need of an SPI loopback > test? Am I missing something and there is a solution already available? Best regards, Krzysztof