linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: msm8939: Make blsp

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Message-ID: <cd8af752-34ec-4ac3-8713-08add7d29b32@linaro.org>
Date:   Mon, 4 Dec 2023 11:59:57 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: qcom: msm8939: Make blsp_dma
 controlled-remotely

On 04/12/2023 11:21, Stephan Gerhold wrote:
> The blsp_dma controller is shared between the different subsystems,
> which is why it is already initialized by the firmware. We should not
> reinitialize it from Linux to avoid potential other users of the DMA
> engine to misbehave.
> 
> In mainline this can be described using the "qcom,controlled-remotely"
> property. In the downstream/vendor kernel from Qualcomm there is an
> opposite "qcom,managed-locally" property. This property is *not* set
> for the qcom,sps-dma@...4000 [1] so adding "qcom,controlled-remotely"
> upstream matches the behavior of the downstream/vendor kernel.
> 
> Adding this seems to fix some weird issues with UART where both
> input/output becomes garbled with certain obscure firmware versions on
> some devices.
> 
> [1]: https://git.codelinaro.org/clo/la/kernel/msm-3.10/-/blob/LA.BR.1.2.9.1-02310-8x16.0/arch/arm/boot/dts/qcom/msm8939-common.dtsi#L866-872
> 
> Cc: <stable@...r.kernel.org> # 6.5
> Fixes: 61550c6c156c ("arm64: dts: qcom: Add msm8939 SoC")
> Signed-off-by: Stephan Gerhold <stephan@...hold.net>
> ---
> This should only be backported to v6.5+ since it depends on commit
> 8975dd41a9db ("dmaengine: qcom: bam_dma: allow omitting
> num-{channels,ees}") which landed in v6.5.
> ---
>   arch/arm64/boot/dts/qcom/msm8939.dtsi | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/msm8939.dtsi b/arch/arm64/boot/dts/qcom/msm8939.dtsi
> index 95610a32750a..9eb8f1ceee99 100644
> --- a/arch/arm64/boot/dts/qcom/msm8939.dtsi
> +++ b/arch/arm64/boot/dts/qcom/msm8939.dtsi
> @@ -1761,6 +1761,7 @@ blsp_dma: dma-controller@...4000 {
>   			clock-names = "bam_clk";
>   			#dma-cells = <1>;
>   			qcom,ee = <0>;
> +			qcom,controlled-remotely;
>   		};
>   
>   		blsp_uart1: serial@...f000 {
> 

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>