Commit 60df5de9 authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

nvme: cleanup nvme_configure_apst 



Remove a level of indentation from the main code implementating the table
search by using a goto for the APST not supported case.  Also move the
main comment above the function.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarNiklas Cassel <niklas.cassel@wdc.com>
parent 53fe2a30

drivers/nvme/host/core.c

+69 −80
Original line number Diff line number Diff line
@@ -2181,28 +2181,28 @@ static int nvme_configure_acre(struct nvme_ctrl *ctrl) 
	return ret;

}



static int nvme_configure_apst(struct nvme_ctrl *ctrl)

{

/*

	 * APST (Autonomous Power State Transition) lets us program a

	 * table of power state transitions that the controller will

	 * perform automatically.  We configure it with a simple

	 * heuristic: we are willing to spend at most 2% of the time

	 * transitioning between power states.  Therefore, when running

	 * in any given state, we will enter the next lower-power

	 * non-operational state after waiting 50 * (enlat + exlat)

	 * microseconds, as long as that state's exit latency is under

	 * the requested maximum latency.

 * APST (Autonomous Power State Transition) lets us program a table of power

 * state transitions that the controller will perform automatically.

 * We configure it with a simple heuristic: we are willing to spend at most 2%

 * of the time transitioning between power states.  Therefore, when running in

 * any given state, we will enter the next lower-power non-operational state

 * after waiting 50 * (enlat + exlat) microseconds, as long as that state's exit

 * latency is under the requested maximum latency.

 *

 * We will not autonomously enter any non-operational state for which the total

 * latency exceeds ps_max_latency_us.

 *

	 * We will not autonomously enter any non-operational state for

	 * which the total latency exceeds ps_max_latency_us.  Users

	 * can set ps_max_latency_us to zero to turn off APST.

 * Users can set ps_max_latency_us to zero to turn off APST.

 */



	unsigned apste;

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;



	/*
@@ -2223,17 +2223,15 @@ static int nvme_configure_apst(struct nvme_ctrl *ctrl) 


	if (!ctrl->apst_enabled || ctrl->ps_max_latency_us == 0) {

		/* Turn off APST. */

		apste = 0;

		dev_dbg(ctrl->device, "APST disabled\n");

	} else {

		__le64 target = cpu_to_le64(0);

		int state;

		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.

	 * 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;
@@ -2242,64 +2240,55 @@ static int nvme_configure_apst(struct nvme_ctrl *ctrl) 
			table->entries[state] = target;



		/*

			 * Don't allow transitions to the deepest state

			 * if it's quirked off.

		 * 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?

		 * 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))

		if (!(ctrl->psd[state].flags & NVME_PS_FLAGS_NON_OP_STATE))

			continue;



			exit_latency_us =

				(u64)le32_to_cpu(ctrl->psd[state].exit_lat);

		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 +

		total_latency_us = exit_latency_us +

			le32_to_cpu(ctrl->psd[state].entry_lat);



		/*

			 * This state is good.  Use it as the APST idle

			 * target for higher power states.

		 * This state is good.  Use it as the APST idle target for

		 * higher power states.

		 */

		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));



		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;

	}



		apste = 1;



		if (max_ps == -1) {

	if (max_ps == -1)

		dev_dbg(ctrl->device, "APST enabled but no non-operational states are available\n");

		} else {

	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;

}