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

[Cristian Ciocaltea via Alsa-devel <alsa-devel@alsa-project.org>]

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From: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
To: Conor Dooley <conor@kernel.org>, Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>, Cristian Marussi <cristian.marussi@arm.com>, Rob Herring <robh+dt@kernel.org>, 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>, 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: Fri, 17 Mar 2023 19:43:53 +0200
Message-ID: <e81f02f2-e692-e4ef-1510-fdc285dd5964@collabora.com>

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..

> Cheers,
> Conor