linux-kernel - Re: [PATCH 2/2] soc: qcom: rmtfs: Support dynamic placement of region

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Date:   Tue, 30 May 2023 21:48:46 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] soc: qcom: rmtfs: Support dynamic placement of region

On Tue, May 30, 2023 at 12:34:36PM -0700, Bjorn Andersson wrote:
> In some configurations, the exact placement of the rmtfs shared memory
> region isn't so strict. In the current implementation the author of the
> DeviceTree source is forced to make up a memory region.
> 
> Extend the rmtfs memory driver to relieve the author of this
> responsibility by introducing support for using dynamic allocation in
> the driver.
> 
> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> ---
>  arch/arm64/boot/dts/qcom/sdm845-mtp.dts | 10 ++++
>  drivers/soc/qcom/rmtfs_mem.c            | 66 +++++++++++++++++++------
>  2 files changed, 61 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sdm845-mtp.dts b/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> index d1440b790fa6..e6191b8ba4c6 100644
> --- a/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> +++ b/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> @@ -12,6 +12,8 @@
>  #include "pm8998.dtsi"
>  #include "pmi8998.dtsi"
>  
> +/delete-node/ &rmtfs_mem;
> +
>  / {
>  	model = "Qualcomm Technologies, Inc. SDM845 MTP";
>  	compatible = "qcom,sdm845-mtp", "qcom,sdm845";
> @@ -48,6 +50,14 @@ vreg_s4a_1p8: pm8998-smps4 {
>  		vin-supply = <&vph_pwr>;
>  	};
>  
> +	rmtfs {
> +		compatible = "qcom,rmtfs-mem";
> +
> +		qcom,alloc-size = <(2*1024*1024)>;
> +		qcom,client-id = <1>;
> +		qcom,vmid = <15>;
> +	};
> +

Couldn't you just use the existing dynamic allocation of
reserved-memory, without any driver changes?

/ {
	reserved-memory {
		rmtfs {
			compatible = "qcom,rmtfs-mem";
			size = <0x0 (2*1024*1024)>;
			alignment = <0x0 ...>; // if you want a special one
			no-map; // don't we want to map this actually?

			qcom,client-id = <1>;
			qcom,vmid = <15>;
		};
	};
};

You won't get the 4K empty pages but I guess you just have them because
you allocate the memory without proper alignment?

Related patch series where I propose using it for most firmware memory
regions:
https://lore.kernel.org/linux-arm-msm/20230510-dt-resv-bottom-up-v1-5-3bf68873dbed@gerhold.net/

Thanks,
Stephan