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

Cristian Ciocaltea cristian.ciocaltea at collabora.com
Fri Mar 17 10:43:53 PDT 2023

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 at 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

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