linux-kernel - Re: [PATCH V7 2/2] firmware: qcom: scm: Add wait-queue handling logic

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Date:   Tue, 10 Jan 2023 00:14:11 -0800
From:   Guru Das Srinagesh <quic_gurus@...cinc.com>
To:     Sibi Sankar <quic_sibis@...cinc.com>
CC:     <andersson@...nel.org>, <agross@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <robh+dt@...nel.org>,
        <konrad.dybcio@...ainline.org>, <robimarko@...il.com>
Subject: Re: [PATCH V7 2/2] firmware: qcom: scm: Add wait-queue handling logic

On Jan 10 2023 12:07, Sibi Sankar wrote:

...

> +static int __scm_smc_do_quirk_handle_waitq(struct device *dev, struct arm_smccc_args *waitq,
> +					   struct arm_smccc_res *res)
> +{
> +	int ret;
> +	struct arm_smccc_args resume;
> +	u32 wq_ctx, smc_call_ctx, flags;
> +	struct arm_smccc_args *smc = waitq;
> +
> +	do {
> +		__scm_smc_do_quirk(smc, res);
> +
> +		if (res->a0 == QCOM_SCM_WAITQ_SLEEP) {
> +			wq_ctx = res->a1;
> +			smc_call_ctx = res->a2;
> +			flags = res->a3;
> +
> +			if (!dev)
> +				return -EPROBE_DEFER;
> +
> +			ret = qcom_scm_lookup_completion(wq_ctx);

I see that this function has been created in response to Bjorn's comment [1]
about avoiding the dev_get_drvdata() call, but I would prefer to not use this
function as it hides the fact that the wait_for_completion() is occurring here.

Knowing where the waiting is happening is useful not just for understanding
code flow but also for debugging issues in the future.

...

> +static struct completion *qcom_scm_lookup_wq(struct qcom_scm *scm, u32 wq_ctx)
> +{

This function is called qcom_scm_lookup_wq() but there is no looking up
occurring here. Could this comment be added for context?

/* FW currently only supports a single wq_ctx (zero).
 * TODO: Update this logic to include dynamic allocation and lookup of
 * completion structs when FW supports more wq_ctx values.
 */

> +	/* assert wq_ctx is zero */
> +	if (wq_ctx != 0) {
> +		dev_err(scm->dev, "No waitqueue found for wq_ctx %d\n", wq_ctx);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	return &scm->waitq_comp;
> +}
> +
...

[1] https://lore.kernel.org/lkml/20221208221125.bflo7unhcrgfsgbr@builder.lan/