linux-kernel - Re: [PATCH 08/10] ARM: dts: exynos: use proper 'dma-channels/requests' properties

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Date:   Thu, 28 Apr 2022 12:09:02 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org, Dinh Nguyen <dinguyen@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Michal Simek <michal.simek@...inx.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Scott Branden <sbranden@...adcom.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        linux-samsung-soc@...r.kernel.org,
        Broadcom Kernel Team <bcm-kernel-feedback-list@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Liviu Dudau <liviu.dudau@....com>, Ray Jui <rjui@...adcom.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 08/10] ARM: dts: exynos: use proper
 'dma-channels/requests' properties

On 28/04/2022 12:05, Marek Szyprowski wrote:
>>>>> I also don't see any code that would read those properties. IMHO they
>>>>> should be simply removed at all, at least for the PL330 related nodes.
>>>> In current Linux implementation they indeed are not used. Nothing parses
>>>> them. However:
>>>> 1. They describe (hopefully correct) the hardware.
>>>> 2. They might be used by other implementations of pl330 driver.
>>>>
>>>> I would not remove them from existing sources, but indeed maybe there is
>>>> no need to add for new files.
>>> What's the point in having dt properties duplicating data that might be
>>> read from the driver registers?
>> Hm, indeed, there is no point in this. Since they are read from
>> registers, what was the idea behind in commit 42cf20980cde?
> 
> #dma-cells is indeed required, but the rest seems to be the cargo-cult 
> of some kind.

Rob,

Any guidance from your side? Is there any benefit in describing the
hadrware (dma-channels/dma-requests) if the same value can be read from
registers?


Best regards,
Krzysztof