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

From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: Robin Murphy <robin.murphy@arm.com>,
	Lee Jones <lee.jones@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Alim Akhtar <alim.akhtar@samsung.com>,
	Dinh Nguyen <dinguyen@kernel.org>,
	Michal Simek <michal.simek@xilinx.com>,
	Liviu Dudau <liviu.dudau@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>,
	Broadcom Kernel Team <bcm-kernel-feedback-list@broadcom.com>,
	Sylwester Nawrocki <s.nawrocki@samsung.com>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Subject: Re: [PATCH 04/10] arm64: dts: juno: use proper 'dma-channels/requests' properties
Date: Thu, 28 Apr 2022 12:45:17 +0200	[thread overview]
Message-ID: <d8448fa4-3cec-db1c-c132-d875cab61572@linaro.org> (raw)
In-Reply-To: <1d1aae6e-50db-d6db-9727-62f9c2d1ca6b@arm.com>

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@kernel.org>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.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@7ff00000 {
>>   		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