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

[Bjorn Andersson]

On Tue, Jan 10, 2023 at 12:14:11AM -0800, Guru Das Srinagesh wrote:
> 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.
> 

My reasoning here is that I don't want the waiting for the completion
that happen in one part of the driver and the completion happening in a
completely different one.

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

Absolutely agree, this should be named to make that obvious to the
reader.

> ...
> 
> > +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.
>  */
> 

Agree.

Regards,
Bjorn

> > +	/* 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@xxxxxxxxxxx/