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

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Message-ID: <e81f02f2-e692-e4ef-1510-fdc285dd5964@collabora.com>
Date:   Fri, 17 Mar 2023 19:43:53 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To:     Conor Dooley <conor@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Nicolas Frattaroli <frattaroli.nicolas@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Drake <drake@...lessm.com>,
        Katsuhiro Suzuki <katsuhiro@...suster.net>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        alsa-devel@...a-project.org, linux-rockchip@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH 02/11] dt-bindings: serial: snps-dw-apb-uart: Relax
 dma-names order constraint

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@...30000: 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