Re: [PATCH 02/11] dt-bindings: serial: snps-dw-apb-uart: Relax dma-names order constraint

From: Rob Herring <robh@kernel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Cc: Conor Dooley <conor@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Cristian Marussi <cristian.marussi@arm.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Nicolas Frattaroli <frattaroli.nicolas@gmail.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Daniel Drake <drake@endlessm.com>,
	Katsuhiro Suzuki <katsuhiro@katsuster.net>,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org,
	alsa-devel@alsa-project.org, linux-rockchip@lists.infradead.org,
	linux-riscv@lists.infradead.org, kernel@collabora.com
Subject: Re: [PATCH 02/11] dt-bindings: serial: snps-dw-apb-uart: Relax dma-names order constraint
Date: Mon, 20 Mar 2023 11:01:37 -0500	[thread overview]
Message-ID: <20230320160137.GB1755078-robh@kernel.org> (raw)
In-Reply-To: <e81f02f2-e692-e4ef-1510-fdc285dd5964@collabora.com>

On Fri, Mar 17, 2023 at 07:43:53PM +0200, Cristian Ciocaltea wrote:
> On 3/17/23 18:26, Conor Dooley wrote:
> > On Fri, Mar 17, 2023 at 04:54:47PM +0100, Krzysztof Kozlowski wrote:
> > > On 17/03/2023 11:21, Cristian Ciocaltea wrote:
> > > > On 3/17/23 10:31, Krzysztof Kozlowski wrote:
> > > > > On 15/03/2023 12:47, Cristian Ciocaltea wrote:
> > > > > > Commit 370f696e4474 ("dt-bindings: serial: snps-dw-apb-uart: add dma &
> > > > > > dma-names properties") documented dma-names property to handle Allwiner
> > > > > > D1 dtbs_check warnings, but relies on a strict rx->tx ordering, which is
> > > > > > the reverse of what a different board expects:
> > > > > > 
> > > > > >     rk3326-odroid-go2.dtb: serial@ff030000: dma-names:0: 'rx' was expected
> > > > > > 
> > > > > > A quick and incomplete check shows the inconsistency is present in many
> > > > > > other DT files:
> > > > > 
> > > > > Why not fixing the DTS? The properties should have fixed order.
> > > > 
> > > > I was initially concerned about the risk of a potential ABI breakage,
> > > > but I think that's not really a problem since dma-names is not directly
> > > > accessed in the driver and DT Kernel API doesn't rely on a particular order.
> > > > 
> > > > If there are no objections, I would switch the order in the binding to
> > > > tx->rx, since that's what most of the DTS use, and fix the remaining ones.
> > > 
> > > Since we added the order recently, I rather assume it is the correct or
> > > preferred one.
> > 
> > IIRC I checked around the other serial bindings & there was not a
> > consistent order that all serial bindings used, so I picked the order that
> > was used across the various allwinner boards that do use dma-names.
> 
> Thanks for clarifying this, Conor! Would it be fine to switch to tx->rx
> order as it requires less changes to fix the inconsistencies?
> 
> > Before changing dts files, it's probably a good idea to make sure that
> > the dma-names are not used somewhere outside of Linux.
> 
> Right, that means we cannot exclude the ABI breakage concern. Not sure how
> easy would be to actually verify this. Hence I wonder if there is really no
> chance to allow the flexible order in the binding..

If it changes and someone complains, then yes we'll allow flexible 
order.

Rob