linux-kernel - Re: [PATCH v2 2/3] soc: qcom: qcom_stats: Add QMP support for syncing ddr stats

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Message-ID: <jl4g7mutb65ifxuv3covropjntziv5enxyc3lgz2fi7ddu64bd@e726p6by3vfh>
Date: Wed, 21 May 2025 15:52:25 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Maulik Shah <maulik.shah@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2 2/3] soc: qcom: qcom_stats: Add QMP support for
 syncing ddr stats

On Wed, May 21, 2025 at 02:02:11PM +0530, Maulik Shah wrote:
> Recent SoCs (SM8450 onwards) require QMP command to be sent before reading
> ddr stats. The duration field of ddr stats will get populated only if QMP
> command is sent.
> 
> Add support to send ddr stats freqsync QMP command.
> 
> Signed-off-by: Maulik Shah <maulik.shah@....qualcomm.com>
> ---
>  drivers/soc/qcom/qcom_stats.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> @@ -310,6 +329,14 @@ static int qcom_stats_probe(struct platform_device *pdev)
>  	qcom_create_subsystem_stat_files(root, config);
>  	qcom_create_soc_sleep_stat_files(root, reg, d, config);
>  	qcom_create_ddr_stat_files(root, reg, config);
> +	/*
> +	 * QMP is used for DDR stats syncing to MSG RAM for recent SoCs (SM8450 onwards).
> +	 * The prior SoCs do not need QMP handle as the required stats are already present
> +	 * in MSG RAM, provided the DDR_STATS_MAGIC_KEY matches.
> +	 */
> +	qcom_stats_qmp = qmp_get(&pdev->dev);
> +	if (IS_ERR(qcom_stats_qmp))
> +		qcom_stats_qmp = NULL;

Don't we need to handle QMP being not probed _yet_? In other words,
there are several distinct cases:

- No QMP defined, proceed without it
- QMP defined, not probed yet, return -EPROBE_DEFER here
- QMP defined, qmp_get() returns an error, return that error code
- QMP defined, qmp_get() returned valid pointer, proceed with using it.

>  
>  	platform_set_drvdata(pdev, root);
>  
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry