static int nvme_configure_apst()

in host/core.c [2332:2435]

• 67 lines of code
• 20 McCabe index (conditional complexity)

static int nvme_configure_apst(struct nvme_ctrl *ctrl)
{
	struct nvme_feat_auto_pst *table;
	unsigned apste = 0;
	u64 max_lat_us = 0;
	__le64 target = 0;
	int max_ps = -1;
	int state;
	int ret;
	unsigned last_lt_index = UINT_MAX;

	/*
	 * If APST isn't supported or if we haven't been initialized yet,
	 * then don't do anything.
	 */
	if (!ctrl->apsta)
		return 0;

	if (ctrl->npss > 31) {
		dev_warn(ctrl->device, "NPSS is invalid; not using APST\n");
		return 0;
	}

	table = kzalloc(sizeof(*table), GFP_KERNEL);
	if (!table)
		return 0;

	if (!ctrl->apst_enabled || ctrl->ps_max_latency_us == 0) {
		/* Turn off APST. */
		dev_dbg(ctrl->device, "APST disabled\n");
		goto done;
	}

	/*
	 * Walk through all states from lowest- to highest-power.
	 * According to the spec, lower-numbered states use more power.  NPSS,
	 * despite the name, is the index of the lowest-power state, not the
	 * number of states.
	 */
	for (state = (int)ctrl->npss; state >= 0; state--) {
		u64 total_latency_us, exit_latency_us, transition_ms;

		if (target)
			table->entries[state] = target;

		/*
		 * Don't allow transitions to the deepest state if it's quirked
		 * off.
		 */
		if (state == ctrl->npss &&
		    (ctrl->quirks & NVME_QUIRK_NO_DEEPEST_PS))
			continue;

		/*
		 * Is this state a useful non-operational state for higher-power
		 * states to autonomously transition to?
		 */
		if (!(ctrl->psd[state].flags & NVME_PS_FLAGS_NON_OP_STATE))
			continue;

		exit_latency_us = (u64)le32_to_cpu(ctrl->psd[state].exit_lat);
		if (exit_latency_us > ctrl->ps_max_latency_us)
			continue;

		total_latency_us = exit_latency_us +
			le32_to_cpu(ctrl->psd[state].entry_lat);

		/*
		 * This state is good. It can be used as the APST idle target
		 * for higher power states.
		 */
		if (apst_primary_timeout_ms && apst_primary_latency_tol_us) {
			if (!nvme_apst_get_transition_time(total_latency_us,
					&transition_ms, &last_lt_index))
				continue;
		} else {
			transition_ms = total_latency_us + 19;
			do_div(transition_ms, 20);
			if (transition_ms > (1 << 24) - 1)
				transition_ms = (1 << 24) - 1;
		}

		target = cpu_to_le64((state << 3) | (transition_ms << 8));
		if (max_ps == -1)
			max_ps = state;
		if (total_latency_us > max_lat_us)
			max_lat_us = total_latency_us;
	}

	if (max_ps == -1)
		dev_dbg(ctrl->device, "APST enabled but no non-operational states are available\n");
	else
		dev_dbg(ctrl->device, "APST enabled: max PS = %d, max round-trip latency = %lluus, table = %*phN\n",
			max_ps, max_lat_us, (int)sizeof(*table), table);
	apste = 1;

done:
	ret = nvme_set_features(ctrl, NVME_FEAT_AUTO_PST, apste,
				table, sizeof(*table), NULL);
	if (ret)
		dev_err(ctrl->device, "failed to set APST feature (%d)\n", ret);
	kfree(table);
	return ret;
}