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 0AE293E9C26; Wed, 20 May 2026 14:21:08 +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=1779286870; cv=none; b=He9HDpaG4sa8f+Yei5+hDskGrXazOLzZHP+QwRDSle6B7TRCSHaj8xFacPr7wc3nT8xoPVXJ3Qg2LQaIxa6sADPpXB/Q3DlTwsvOWdwoc1Y4RkY/Kya1I2w4Wjxw7b2Ycuq3GbGzjM7jvpCtn2NiPPBDZsvKXqgjN6IghbiRuaw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779286870; c=relaxed/simple; bh=o80hkq12hOv7CQPqQD1IVh5XcVb6g3yssgV/Fs94Xn4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aMdM3+OSk/1pOtfVe4+JCnRmcCQXtxsOByAQuXnOjnfwLM8+oFINioZVLDklKC4EYmtnhDjZEpa3qxc94bmMZBPJpupF8mZ2vfXOxMNAMOl4EGPk/ge+smUx6aMy2Fjl2VGP2lbF1W5+pPegrrnEJ/mxdhg9B+9NER8oK59cggU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a1gP1izC; 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="a1gP1izC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D35151F000E9; Wed, 20 May 2026 14:21:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779286868; bh=dSkU8KGuf/aJKSMYjpXAmPN07Ebv/tBk5PSaYaKcXw8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=a1gP1izCH1gFkaBAfxYL/OKky9tykxq88oQ0xOsm60nhGJyaDqmaHdK2qWe6tzV3F 7se4PhhKLhSfwXvzF+TqemmAu1xcLD2RcUyjoBQJJnRtNx9AtGz5MFNgCMQtzVEQEJ 56PARB2/72wrzzrBj3Km/TH9bypwxoRtGTaxNlbWVFJVAYBSeYmvuisziIEmqBtG3P oiXaXQ49+jZ98tXVzi/+/cKvzSEFs7r9APAf5BggSgcFpk7VZIalEF0AJKPvHSKT2O 3rytpDaXkagwzn76yl7jOcVZhmCR3KeaLKWEl3hrdkDhn2h5d0FgoZP4EFxIjc3/hC otAhKdBKYQuCQ== Message-ID: <3eaa70e0-4284-4c35-a5d5-42afa3087eea@kernel.org> Date: Wed, 20 May 2026 16:21:05 +0200 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: [PATCH 1/2] spi: dt-bindings: cdns,xspi: add sdma-io-width To: Jisheng Zhang Cc: Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , linux-spi@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260511031732.3199-1-jszhang@kernel.org> <20260511031732.3199-2-jszhang@kernel.org> <20260515-expert-devious-cricket-faff56@quoll> <21d30826-bfe6-44cd-8c89-c1986f539e48@kernel.org> <14719378-7bf5-4688-81e9-bccedf618d18@kernel.org> <37a3e9dd-88c2-4d8d-8ae4-6037a1eeedcc@kernel.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 20/05/2026 15:18, Jisheng Zhang wrote: > On Wed, May 20, 2026 at 03:22:07PM +0200, Krzysztof Kozlowski wrote: >> On 20/05/2026 14:30, Mark Brown wrote: >>> On Wed, May 20, 2026 at 02:16:21PM +0200, Krzysztof Kozlowski wrote: >>>> On 20/05/2026 13:48, Jisheng Zhang wrote: >>> >>>>> If you mean "Why this cannot be deduced from the compatible?", I think >>>>> the slave dma port is part of the cdns xspi, so its io width belongs >>>>> to xSPI device property. >>>>> From another side, we have seen such property in other drivers such as >>>>> the reg-io-width for the dw spi DW_SPI_DR port io width. >>> >>>> So you mean it depends on SPI device? Then why spi-peripheral-props is >>>> not applicable here? >>> >>> That will be controller side, not device side. >>> >>>> If this is not bus width, but DMA-something, is not really then SPI >>>> device dependent, but rather DMA controller limitation, so either >>>> deducible from compatible or something else is missing here. >>> >>> My understanding is that this is a connection between the SPI and DMA >>> controllers so it's not as obvious as it could be which side of that >>> link should have the property, eg: >>> >>> https://www.cadence.com/content/dam/cadence-www/global/en_US/documents/tools/silicon-solutions/design-ip/controller-ip-qspi.pdf >>> >>> shows a separate direct connection between the DMA controller and the >>> xSPI controller, the DMA controller isn't interacting with registers on >>> the CPU visible buses. The width is probably a design time configurable >>> option on both sides of the link. >> >> Yes and that sounds a lot specific to particular controller, thus should >> be implied by / deducible from the compatible. > > This is IP feature, so if we couple the IP's feature with platform > compatible, I would see some unnecessary LoCs. For example, > Let's assume the IP has 10 users, they all support 4 bytes io width, > other features are the same. > > If implied by the compatible string, we need to add 10 compatible > string support both in code and dt-bindings. You always need 10 compatible strings in bindings. But driver would need only one, since devices are compatible as you described. > > vs > > If supported by "sdma-io-width", nothing is needed after this patch > > IMHO, the 2nd sounds better, what do you think? We answered this in writing bindings. Properties are not replacement for specific compatible. I don't know how to write that sentence in bindings clearer - it's exactly this case. Best regards, Krzysztof