linux-kernel - Re: [PATCH v2 3/4] ASoC: dt-bindings: fsl-sai: allow only one dma-names

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Date: Mon, 4 Mar 2024 20:13:06 +0000
From: Conor Dooley <conor@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Shengjiu Wang <shengjiu.wang@....com>, linux-sound@...r.kernel.org,
	devicetree@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] ASoC: dt-bindings: fsl-sai: allow only one
 dma-names

On Fri, Mar 01, 2024 at 12:25:44PM -0500, Frank Li wrote:
> On Fri, Mar 01, 2024 at 05:07:07PM +0000, Conor Dooley wrote:
> > On Fri, Mar 01, 2024 at 11:46:20AM -0500, Frank Li wrote:
> > > On Fri, Mar 01, 2024 at 04:05:25PM +0000, Conor Dooley wrote:
> > > > On Thu, Feb 29, 2024 at 02:38:24PM -0500, Frank Li wrote:
> > > > > On Thu, Feb 29, 2024 at 06:57:29PM +0000, Conor Dooley wrote:
> > > > > > On Thu, Feb 29, 2024 at 06:55:58PM +0000, Conor Dooley wrote:
> > > > > > > On Tue, Feb 27, 2024 at 03:54:11PM -0500, Frank Li wrote:
> > > > > > > > Some sai only connect one direction. So allow only "rx" or "tx" for
> > > > > > > > dma-names.
> > > > > > > 
> > > > > > > Which sai? Can you restrict this per compatible please, so that someone
> > > > > > > cannot add 2 dmas for ones where only the tx is supported.
> > > > > > > 
> > > > > > > |  dmas:
> > > > > > > |    minItems: 1
> > > > > > > |    items:
> > > > > > > |      - description: DMA controller phandle and request line for RX
> > > > > > > |      - description: DMA controller phandle and request line for TX
> > > > > > > 
> > > > > > > The binding already allows only one, but it documents that the first dma
> > > > > > > is always the RX dma, and that doesn't change with this patch..
> > > > > > 
> > > > > > I said "doesn't change" - but I don't think you can change this
> > > > > > trivially, as something could rely on the first dma being the rx one.
> > > > > > You'd have to check that there is nothing using these using indices
> > > > > > rather than names before making any changes here.
> > > > > 
> > > > > Linux driver and dts with tx only work well. Only issue is dtb_check will
> > > > > report error. I want to eliminate these DTB_CHECK warning.
> > > > 
> > > > Linux is not the only user of these bindings, citing linux as your
> > > > evidence here is only sufficient if no other users exist. Do they?
> > > 
> > > But, 'dmas' should be common property for all these bindings? I don't think
> > > they use 'descriptions:' property, which should guide dts writer to write
> > > dts file. actually words 'DMA controller phandle and request line' just
> > > nonsense words. let 'regs', it'd better descript at 'reg-names' instead
> > > of 'regs' if reg-names exist. Only meansful words is "RX" and "TX", which
> > > already show at "dma-names".
> > 
> > None of this matters. If there's a documented order for these, which
> > there is, software is not obligated to use the names and can rely on the
> > order alone. You need to check that there are no other users which will
> > be broken by your proposed change.
> 
> As my best knowledge, only linux use this binding.

If you've checked and there are no users, that's fine. Please mention
in the commit message that there are no users that will be affected as
justification for the ABI change.

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