linux-kernel - Re: [PATCH 04/10] arm64: dts: juno: use proper 'dma-channels/requests' properties

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Date:   Thu, 28 Apr 2022 12:45:17 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Robin Murphy <robin.murphy@....com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Liviu Dudau <liviu.dudau@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Broadcom Kernel Team <bcm-kernel-feedback-list@...adcom.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 04/10] arm64: dts: juno: use proper
 'dma-channels/requests' properties

On 28/04/2022 12:43, Robin Murphy wrote:
> On 2022-04-27 16:58, Krzysztof Kozlowski wrote:
>> pl330 DMA controller bindings documented 'dma-channels' and
>> 'dma-requests' properties (without leading hash sign), so fix the DTS to
>> match the bindings.
>>
>> Reported-by: Rob Herring <robh@...nel.org>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> ---
>>   arch/arm64/boot/dts/arm/juno-base.dtsi | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/arm/juno-base.dtsi b/arch/arm64/boot/dts/arm/juno-base.dtsi
>> index 4f40a5c8f565..96ef0ddc0b2d 100644
>> --- a/arch/arm64/boot/dts/arm/juno-base.dtsi
>> +++ b/arch/arm64/boot/dts/arm/juno-base.dtsi
>> @@ -829,8 +829,8 @@ dma-controller@...00000 {
>>   		compatible = "arm,pl330", "arm,primecell";
>>   		reg = <0x0 0x7ff00000 0 0x1000>;
>>   		#dma-cells = <1>;
>> -		#dma-channels = <8>;
>> -		#dma-requests = <32>;
>> +		dma-channels = <8>;
>> +		dma-requests = <32>;
> 
> BTW, this has always been wrong - Juno is configured with only 8 request 
> interfaces. But then it's moot anyway since PL330 has an ID register for 
> this stuff[1], so the DT properties aren't used by Linux, and shouldn't 
> be needed in general.

Marek also raised the point [1] that these properties are useless for
PL330 because the actual data is read from the device registers.

I understand you are also supporting the idea of removing them from
pl330 device nodes?

[1]
https://lore.kernel.org/linux-devicetree/20220427155840.596535-1-krzysztof.kozlowski@linaro.org/T/#mf108b8c9f0d513ebc6e381775e3c6887b5c2fe31

Best regards,
Krzysztof