linux-kernel - Re: [PATCH v1 2/5] arm64: dts: qcom: Add support for configuring channel TRE size

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Message-ID: <658c19c7-9eeb-4329-aa96-a4a9b09d7117@kernel.org>
Date: Thu, 17 Oct 2024 09:10:39 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>,
 Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>,
 Andi Shyti <andi.shyti@...nel.org>, Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 cros-qcom-dts-watchers@...omium.org, linux-arm-msm@...r.kernel.org,
 dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, quic_msavaliy@...cinc.com,
 quic_vtanuku@...cinc.com
Subject: Re: [PATCH v1 2/5] arm64: dts: qcom: Add support for configuring
 channel TRE size

On 16/10/2024 16:35, Bjorn Andersson wrote:
>>> @@ -1064,7 +1064,7 @@
>>>  		};
>>>  
>>>  		gpi_dma0: dma-controller@...000 {
>>> -			#dma-cells = <3>;
>>> +			#dma-cells = <4>;
>>>  			compatible = "qcom,sc7280-gpi-dma", "qcom,sm6350-gpi-dma";
>>>  			reg = <0 0x00900000 0 0x60000>;
>>>  			interrupts = <GIC_SPI 244 IRQ_TYPE_LEVEL_HIGH>,
>>> @@ -1114,8 +1114,8 @@
>>>  							"qup-memory";
>>>  				power-domains = <&rpmhpd SC7280_CX>;
>>>  				required-opps = <&rpmhpd_opp_low_svs>;
>>> -				dmas = <&gpi_dma0 0 0 QCOM_GPI_I2C>,
>>> -				       <&gpi_dma0 1 0 QCOM_GPI_I2C>;
>>> +				dmas = <&gpi_dma0 0 0 QCOM_GPI_I2C 64>,
>>> +				       <&gpi_dma0 1 0 QCOM_GPI_I2C 64>;
>>
>> So everywhere is 64, thus this is fixed. Deduce it from the compatible
>>
> 
> If I understand correctly, it's a software tunable property, used to
> balance how many TRE elements that should be preallocated.
> 
> If so, it would not be a property of the hardware/compatible, but rather
> a result of profiling and a balance between memory "waste" and
> performance.

In such case I would prefer it being runtime-calculated by the driver,
based on frequency or expected bandwidth.

And in any case if this is about to stay, having here default values
means all upstream users don't need it. What's not upstream, does not
exist in such context. We don't add features which are not used by upstream.

Best regards,
Krzysztof