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Subject[PATCH v3 06/10] drivers: qcom: rpmh-rsc: A lot of comments
Date
I've been pouring through the rpmh-rsc code and trying to understand
it. Document everything to the best of my ability. All documentation
here is strictly from code analysis--no actual knowledge of the
hardware was used. If something is wrong in here I either
misunderstood the code, had a typo, or the code has a bug in it
leading to my incorrect understanding.

In a few places here I have documented things that don't make tons of
sense. A future patch will try to address this. While this means I'm
adding comments / todos and then later fixing them in the series, it
seemed more urgent to get things documented first so that people could
understand the later patches.

Any comments I adjusted I also tried to make match kernel-doc better.
Specifically:
- kernel-doc says do not leave a blank line between the function
description and the arguments
- kernel-doc examples always have things starting w/ a capital and
ending with a period.

This should be a no-op. It's just comment changes.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v3:
- Adjusted comments for rpmh_rsc_write_ctrl_data().
- Comments for new enable_tcs_irq() function.
- Comments for new rpmh_rsc_cpu_pm_callback() function.
- Mention in message that I also fixed up kernel-doc stuff.
- Moved comments patch after ("Kill cmd_cache and find_match...").
- One space after a period now (Maulik).
- Plural of TCS fixed to TCSes following Maulik's example.
- Re-added comment in tcs_write() about checking for same address.
- Rebased atop v16 ('Invoke rpmh_flush...') series.
- __tcs_set_trigger() comments adjusted now that it can set or unset.
- get_tcs_for_msg() documents why it's safe to borrow the wake TCS.
- get_tcs_for_msg() no longer returns -EAGAIN.

Changes in v2:
- Document bug of tcs_write() not handling -EAGAIN.
- Document get_tcs_for_msg() => -EAGAIN only for ACTIVE_ONLY.
- Document locks for updating "tcs_in_use" more.
- Document tcs_is_free() without drv->lock OK for tcs_invalidate().
- Document that rpmh_rsc_send_data() can be an implicit invalidate.
- Document two get_tcs_for_msg() issues if zero-active TCS.
- Fixed documentation of "tcs" param in find_slots().
- More clear that active-only xfers can happen on wake TCS sometimes.
- Reword tcs_write() doc a bit.

drivers/soc/qcom/rpmh-internal.h | 62 ++++++---
drivers/soc/qcom/rpmh-rsc.c | 221 ++++++++++++++++++++++++++++---
2 files changed, 246 insertions(+), 37 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
index 6a6d776ccca9..f06350cbc9a2 100644
--- a/drivers/soc/qcom/rpmh-internal.h
+++ b/drivers/soc/qcom/rpmh-internal.h
@@ -22,15 +22,24 @@ struct rsc_drv;
* struct tcs_group: group of Trigger Command Sets (TCS) to send state requests
* to the controller
*
- * @drv: the controller
- * @type: type of the TCS in this group - active, sleep, wake
- * @mask: mask of the TCSes relative to all the TCSes in the RSC
- * @offset: start of the TCS group relative to the TCSes in the RSC
- * @num_tcs: number of TCSes in this type
- * @ncpt: number of commands in each TCS
- * @lock: lock for synchronizing this TCS writes
- * @req: requests that are sent from the TCS
- * @slots: indicates which of @cmd_addr are occupied
+ * @drv: The controller.
+ * @type: Type of the TCS in this group - active, sleep, wake.
+ * @mask: Mask of the TCSes relative to all the TCSes in the RSC.
+ * @offset: Start of the TCS group relative to the TCSes in the RSC.
+ * @num_tcs: Number of TCSes in this type.
+ * @ncpt: Number of commands in each TCS.
+ * @lock: Lock for synchronizing this TCS writes.
+ * @req: Requests that are sent from the TCS; only used for ACTIVE_ONLY
+ * transfers (could be on a wake/sleep TCS if we are borrowing for
+ * an ACTIVE_ONLY transfer).
+ * Start: grab drv->lock, set req, set tcs_in_use, drop drv->lock,
+ * trigger
+ * End: get irq, access req,
+ * grab drv->lock, clear tcs_in_use, drop drv->lock
+ * @slots: Indicates which of @cmd_addr are occupied; only used for
+ * SLEEP / WAKE TCSs. Things are tightly packed in the
+ * case that (ncpt < MAX_CMDS_PER_TCS). That is if ncpt = 2 and
+ * MAX_CMDS_PER_TCS = 16 then bit[2] = the first bit in 2nd TCS.
*/
struct tcs_group {
struct rsc_drv *drv;
@@ -82,19 +91,28 @@ struct rpmh_ctrlr {
* struct rsc_drv: the Direct Resource Voter (DRV) of the
* Resource State Coordinator controller (RSC)
*
- * @name: Controller identifier
- * @tcs_base: Start address of the TCS registers in this controller
- * @id: Instance id in the controller (Direct Resource Voter)
- * @num_tcs: Number of TCSes in this DRV
- * @rsc_pm: CPU PM notifier for controller
- * Used when solver mode is not present
- * @cpus_entered_pm: CPU mask for cpus in idle power collapse
- * Used when solver mode is not present
- * @tcs: TCS groups
- * @tcs_in_use: S/W state of the TCS
- * @lock: Synchronize state of the controller
- * @pm_lock: Synchronize during PM notifications
- * Used when solver mode is not present
+ * @name: Controller identifier.
+ * @tcs_base: Start address of the TCS registers in this controller.
+ * @id: Instance id in the controller (Direct Resource Voter).
+ * @num_tcs: Number of TCSes in this DRV.
+ * @rsc_pm: CPU PM notifier for controller.
+ * Used when solver mode is not present.
+ * @cpus_entered_pm: CPU mask for cpus in idle power collapse.
+ * Used when solver mode is not present.
+ * @tcs: TCS groups.
+ * @tcs_in_use: S/W state of the TCS; only set for ACTIVE_ONLY
+ * transfers, but might show a sleep/wake TCS in use if
+ * it was borrowed for an active_only transfer. You
+ * must hold both the lock in this struct and the
+ * tcs_lock for the TCS in order to mark a TCS as
+ * in-use, but you only need the lock in this structure
+ * (aka the drv->lock) to mark one freed.
+ * @lock: Synchronize state of the controller. If you will be
+ * grabbing this lock and a tcs_lock at the same time,
+ * grab the tcs_lock first so we always have a
+ * consistent lock ordering.
+ * @pm_lock: Synchronize during PM notifications.
+ * Used when solver mode is not present.
* @client: Handle to the DRV's client.
*/
struct rsc_drv {
diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index da1045c92b38..84ae3e514eee 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -171,12 +171,38 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
}
}

+/**
+ * tcs_is_free() - Return if a TCS is totally free.
+ * @drv: The RSC controller.
+ * @tcs_id: The global ID of this TCS.
+ *
+ * Returns true if nobody has claimed this TCS (by setting tcs_in_use).
+ * If the TCS looks free, checks that the hardware agrees.
+ *
+ * Must be called with the drv->lock held or the tcs_lock for the TCS being
+ * tested. If only the tcs_lock is held then it is possible that this
+ * function will return that a tcs is still busy when it has been recently
+ * been freed but it will never return free when a TCS is actually in use.
+ *
+ * Return: true if the given TCS is free.
+ */
static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
{
return !test_bit(tcs_id, drv->tcs_in_use) &&
read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id);
}

+/**
+ * tcs_invalidate() - Invalidate all TCSes of the given type (sleep or wake).
+ * @drv: The RSC controller.
+ * @type: SLEEP_TCS or WAKE_TCS
+ *
+ * This will clear the "slots" variable of the given tcs_group and also
+ * tell the hardware to forget about all entries.
+ *
+ * Return: 0 if no problem, or -EAGAIN if the caller should try again in a
+ * bit. Caller should make sure to enable interrupts between tries.
+ */
static int tcs_invalidate(struct rsc_drv *drv, int type)
{
int m;
@@ -203,9 +229,11 @@ static int tcs_invalidate(struct rsc_drv *drv, int type)
}

/**
- * rpmh_rsc_invalidate - Invalidate sleep and wake TCSes
+ * rpmh_rsc_invalidate() - Invalidate sleep and wake TCSes.
+ * @drv: The RSC controller.
*
- * @drv: the RSC controller
+ * Return: 0 if no problem, or -EAGAIN if the caller should try again in a
+ * bit. Caller should make sure to enable interrupts between tries.
*/
int rpmh_rsc_invalidate(struct rsc_drv *drv)
{
@@ -218,6 +246,18 @@ int rpmh_rsc_invalidate(struct rsc_drv *drv)
return ret;
}

+/**
+ * get_tcs_for_msg() - Get the tcs_group used to send the given message.
+ * @drv: The RSC controller.
+ * @msg: The message we want to send.
+ *
+ * This is normally pretty straightforward except if we are trying to send
+ * an ACTIVE_ONLY message but don't have any active_only TCSes.
+ *
+ * Called without drv->lock held and with no tcs_lock locks held.
+ *
+ * Return: A pointer to a tcs_group or an ERR_PTR.
+ */
static struct tcs_group *get_tcs_for_msg(struct rsc_drv *drv,
const struct tcs_request *msg)
{
@@ -241,7 +281,9 @@ static struct tcs_group *get_tcs_for_msg(struct rsc_drv *drv,
/*
* If we are making an active request on a RSC that does not have a
* dedicated TCS for active state use, then re-purpose a wake TCS to
- * send active votes.
+ * send active votes. This is safe because we ensure any active-only
+ * transfers have finished before we use it (maybe by running from
+ * the last CPU in PM code).
*/
tcs = &drv->tcs[type];
if (msg->state == RPMH_ACTIVE_ONLY_STATE && !tcs->num_tcs)
@@ -250,6 +292,22 @@ static struct tcs_group *get_tcs_for_msg(struct rsc_drv *drv,
return tcs;
}

+/**
+ * get_req_from_tcs() - Get a stashed request that was xfering on the given TCS.
+ * @drv: The RSC controller.
+ * @tcs_id: The global ID of this TCS.
+ *
+ * For ACTIVE_ONLY transfers we want to call back into the client when the
+ * transfer finishes. To do this we need the "request" that the client
+ * originally provided us. This function grabs the request that we stashed
+ * when we started the transfer.
+ *
+ * This only makes sense for ACTIVE_ONLY transfers since those are the only
+ * ones we track sending (the only ones we enable interrupts for and the only
+ * ones we call back to the client for).
+ *
+ * Return: The stashed request.
+ */
static const struct tcs_request *get_req_from_tcs(struct rsc_drv *drv,
int tcs_id)
{
@@ -265,6 +323,23 @@ static const struct tcs_request *get_req_from_tcs(struct rsc_drv *drv,
return NULL;
}

+/**
+ * __tcs_set_trigger() - Start xfer on a TCS or unset trigger on a borrowed TCS
+ * @drv: The controller.
+ * @tcs_id: The global ID of this TCS.
+ * @trigger: If true then untrigger/retrigger. If false then just untrigger.
+ *
+ * In the normal case we only ever call with "trigger=true" to start a
+ * transfer. That will un-trigger/disable the TCS from the last transfer
+ * then trigger/enable for this transfer.
+ *
+ * If we borrowed a wake TCS for an active-only transfer we'll also call
+ * this function with "trigger=false" to just do the un-trigger/disable
+ * before using the TCS for wake purposes again.
+ *
+ * Note that the AP is only in charge of triggering active-only transfers.
+ * The AP never triggers sleep/wake values using this function.
+ */
static void __tcs_set_trigger(struct rsc_drv *drv, int tcs_id, bool trigger)
{
u32 enable;
@@ -289,6 +364,15 @@ static void __tcs_set_trigger(struct rsc_drv *drv, int tcs_id, bool trigger)
}
}

+/**
+ * enable_tcs_irq() - Enable or disable interrupts on the given TCS.
+ * @drv: The controller.
+ * @tcs_id: The global ID of this TCS.
+ * @enable: If true then enable; if false then disable
+ *
+ * We only ever call this when we borrow a wake TCS for an active-only
+ * transfer. For active-only TCSes interrupts are always left enabled.
+ */
static void enable_tcs_irq(struct rsc_drv *drv, int tcs_id, bool enable)
{
u32 data;
@@ -302,7 +386,14 @@ static void enable_tcs_irq(struct rsc_drv *drv, int tcs_id, bool enable)
}

/**
- * tcs_tx_done: TX Done interrupt handler
+ * tcs_tx_done() - TX Done interrupt handler.
+ * @irq: The IRQ number (ignored).
+ * @p: Pointer to "struct rsc_drv".
+ *
+ * Called for ACTIVE_ONLY transfers (those are the only ones we enable the
+ * IRQ for) when a transfer is done.
+ *
+ * Return: IRQ_HANDLED
*/
static irqreturn_t tcs_tx_done(int irq, void *p)
{
@@ -367,6 +458,16 @@ static irqreturn_t tcs_tx_done(int irq, void *p)
return IRQ_HANDLED;
}

+/**
+ * __tcs_buffer_write() - Write to TCS hardware from a request; don't trigger.
+ * @drv: The controller.
+ * @tcs_id: The global ID of this TCS.
+ * @cmd_id: The index within the TCS to start writing.
+ * @msg: The message we want to send, which will contain several addr/data
+ * pairs to program (but few enough that they all fit in one TCS).
+ *
+ * This is used for all types of transfers (active, sleep, and wake).
+ */
static void __tcs_buffer_write(struct rsc_drv *drv, int tcs_id, int cmd_id,
const struct tcs_request *msg)
{
@@ -400,6 +501,26 @@ static void __tcs_buffer_write(struct rsc_drv *drv, int tcs_id, int cmd_id,
write_tcs_reg(drv, RSC_DRV_CMD_ENABLE, tcs_id, cmd_enable);
}

+/**
+ * check_for_req_inflight() - Look to see if conflicting cmds are in flight.
+ * @drv: The controller.
+ * @tcs: A pointer to the tcs_group used for ACTIVE_ONLY transfers.
+ * @msg: The message we want to send, which will contain several addr/data
+ * pairs to program (but few enough that they all fit in one TCS).
+ *
+ * This will walk through the TCSes in the group and check if any of them
+ * appear to be sending to addresses referenced in the message. If it finds
+ * one it'll return -EBUSY.
+ *
+ * Only for use for active-only transfers.
+ *
+ * Must be called with the drv->lock held since that protects tcs_in_use.
+ *
+ * Return: 0 if nothing in flight or -EBUSY if we should try again later.
+ * The caller must re-enable interrupts between tries since that's
+ * the only way tcs_is_free() will ever return true and the only way
+ * RSC_DRV_CMD_ENABLE will ever be cleared.
+ */
static int check_for_req_inflight(struct rsc_drv *drv, struct tcs_group *tcs,
const struct tcs_request *msg)
{
@@ -426,6 +547,15 @@ static int check_for_req_inflight(struct rsc_drv *drv, struct tcs_group *tcs,
return 0;
}

+/**
+ * find_free_tcs() - Find free tcs in the given tcs_group; only for active.
+ * @tcs: A pointer to the active-only tcs_group (or the wake tcs_group if
+ * we borrowed it because there are zero active-only ones).
+ *
+ * Must be called with the drv->lock held since that protects tcs_in_use.
+ *
+ * Return: The first tcs that's free.
+ */
static int find_free_tcs(struct tcs_group *tcs)
{
int i;
@@ -438,6 +568,20 @@ static int find_free_tcs(struct tcs_group *tcs)
return -EBUSY;
}

+/**
+ * tcs_write() - Store messages into a TCS right now, or return -EBUSY.
+ * @drv: The controller.
+ * @msg: The data to be sent.
+ *
+ * Grabs a TCS for ACTIVE_ONLY transfers and writes the messages to it.
+ *
+ * If there are no free TCSes for ACTIVE_ONLY transfers or if a command for
+ * the same address is already transferring returns -EBUSY which means the
+ * client should retry shortly.
+ *
+ * Return: 0 on success, -EBUSY if client should retry, or an error.
+ * Client should have interrupts enabled for a bit before retrying.
+ */
static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
{
struct tcs_group *tcs;
@@ -491,14 +635,26 @@ static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
}

/**
- * rpmh_rsc_send_data: Validate the incoming message and write to the
- * appropriate TCS block.
+ * rpmh_rsc_send_data() - Validate the incoming message + write to TCS block.
+ * @drv: The controller.
+ * @msg: The data to be sent.
*
- * @drv: the controller
- * @msg: the data to be sent
+ * NOTES:
+ * - This is only used for "ACTIVE_ONLY" since the limitations of this
+ * function don't make sense for sleep/wake cases.
+ * - To do the transfer, we will grab a whole TCS for ourselves--we don't
+ * try to share. If there are none available we'll wait indefinitely
+ * for a free one.
+ * - This function will not wait for the commands to be finished, only for
+ * data to be programmed into the RPMh. See rpmh_tx_done() which will
+ * be called when the transfer is fully complete.
+ * - This function must be called with interrupts enabled. If the hardware
+ * is busy doing someone else's transfer we need that transfer to fully
+ * finish so that we can have the hardware, and to fully finish it needs
+ * the interrupt handler to run. If the interrupts is set to run on the
+ * active CPU this can never happen if interrupts are disabled.
*
* Return: 0 on success, -EINVAL on error.
- * Note: This call blocks until a valid data is written to the TCS.
*/
int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
{
@@ -522,13 +678,30 @@ int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
return ret;
}

+/**
+ * find_slots() - Find a place to write the given message.
+ * @tcs: The tcs group to search.
+ * @msg: The message we want to find room for.
+ * @tcs_id: If we return 0 from the function, we return the global ID of the
+ * TCS to write to here.
+ * @cmd_id: If we return 0 from the function, we return the index of
+ * the command array of the returned TCS where the client should
+ * start writing the message.
+ *
+ * Only for use on sleep/wake TCSes since those are the only ones we maintain
+ * tcs->slots for.
+ *
+ * Must be called with the tcs_lock for the group held.
+ *
+ * Return: -ENOMEM if there was no room, else 0.
+ */
static int find_slots(struct tcs_group *tcs, const struct tcs_request *msg,
int *tcs_id, int *cmd_id)
{
int slot, offset;
int i = 0;

- /* Do over, until we can fit the full payload in a TCS */
+ /* Do over, until we can fit the full payload in a single TCS */
do {
slot = bitmap_find_next_zero_area(tcs->slots, MAX_TCS_SLOTS,
i, msg->num_cmds, 0);
@@ -547,12 +720,14 @@ static int find_slots(struct tcs_group *tcs, const struct tcs_request *msg,
}

/**
- * rpmh_rsc_write_ctrl_data: Write request to the controller
+ * rpmh_rsc_write_ctrl_data() - Write request to controller but don't trigger.
+ * @drv: The controller.
+ * @msg: The data to be written to the controller.
*
- * @drv: the controller
- * @msg: the data to be written to the controller
+ * This should only be called for for sleep/wake state, never active-only
+ * state.
*
- * There is no response returned for writing the request to the controller.
+ * Return: 0 if no error; else -error.
*/
int rpmh_rsc_write_ctrl_data(struct rsc_drv *drv, const struct tcs_request *msg)
{
@@ -587,7 +762,6 @@ int rpmh_rsc_write_ctrl_data(struct rsc_drv *drv, const struct tcs_request *msg)

/**
* rpmh_rsc_ctrlr_is_busy() - Check if any of the AMCs are busy.
- *
* @drv: The controller
*
* Checks if any of the AMCs are busy in handling ACTIVE sets.
@@ -623,6 +797,23 @@ static bool rpmh_rsc_ctrlr_is_busy(struct rsc_drv *drv)
return false;
}

+/**
+ * rpmh_rsc_cpu_pm_callback() - Check if any of the AMCs are busy.
+ * @nfb: Pointer to the notifier block in struct rsc_drv.
+ * @action: CPU_PM_ENTER, CPU_PM_ENTER_FAILED, or CPU_PM_EXIT.
+ * @v: Unused
+ *
+ * This function is given to cpu_pm_register_notifier so we can be informed
+ * about when CPUs go down. When all CPUs go down we know no more active
+ * transfers will be started so we write sleep/wake sets. This function gets
+ * called from cpuidle code paths and also at system suspend time.
+ *
+ * If its last CPU going down and AMCs are not busy then writes cached sleep
+ * and wake messages to TCSes. The firmware then takes care of triggering
+ * them when entering deepest low power modes.
+ *
+ * Return: See cpu_pm_register_notifier.
+ */
static int rpmh_rsc_cpu_pm_callback(struct notifier_block *nfb,
unsigned long action, void *v)
{
--
2.26.0.292.g33ef6b2f38-goog
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