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Subject[RFT PATCH 5/9] 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.

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

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

drivers/soc/qcom/rpmh-internal.h | 45 +++---
drivers/soc/qcom/rpmh-rsc.c | 238 ++++++++++++++++++++++++++++---
2 files changed, 248 insertions(+), 35 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
index 6eec32b97f83..49df01af7701 100644
--- a/drivers/soc/qcom/rpmh-internal.h
+++ b/drivers/soc/qcom/rpmh-internal.h
@@ -22,16 +22,23 @@ 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
- * @cmd_cache: flattened cache of cmds in sleep/wake 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.
+ * 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
+ * @cmd_cache: Flattened cache of cmds in sleep/wake TCS; num_tcs * ncpt big.
+ * @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;
@@ -84,14 +91,16 @@ 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
- * @tcs: TCS groups
- * @tcs_in_use: s/w state of the TCS
- * @lock: synchronize state of the controller
- * @client: handle to the DRV's client.
+ * @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.
+ * @tcs: TCS groups.
+ * @tcs_in_use: s/w state of the TCS; only for ACTIVE_ONLY TCSs.
+ * @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.
+ * @client: Handle to the DRV's client.
*/
struct rsc_drv {
const char *name;
diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index a1298035bcd2..190226151029 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -163,12 +163,35 @@ 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 since that protects tcs_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 TCSs 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;
@@ -195,9 +218,11 @@ 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)
{
@@ -210,6 +235,17 @@ 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 TCSs.
+ *
+ * Return: 0 if no problem, or -EGAIN if the caller should try again in a bit.
+ * Caller should make sure to enable interrupts between tries.
+ */
static struct tcs_group *get_tcs_for_msg(struct rsc_drv *drv,
const struct tcs_request *msg)
{
@@ -251,6 +287,22 @@ 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)
{
@@ -267,7 +319,14 @@ static const struct tcs_request *get_req_from_tcs(struct rsc_drv *drv,
}

/**
- * 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 TCSs (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)
{
@@ -277,6 +336,7 @@ static irqreturn_t tcs_tx_done(int irq, void *p)
const struct tcs_request *req;
struct tcs_cmd *cmd;

+ /* NOTE: interrupt status for all TCSs are found in TCS 0 */
irq_status = read_tcs_reg(drv, RSC_DRV_IRQ_STATUS, 0);

for_each_set_bit(i, &irq_status, BITS_PER_LONG) {
@@ -317,6 +377,16 @@ 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 TCSs (active, sleep, and wake).
+ */
static void __tcs_buffer_write(struct rsc_drv *drv, int tcs_id, int cmd_id,
const struct tcs_request *msg)
{
@@ -350,6 +420,11 @@ 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);
}

+/**
+ * __tcs_trigger() - Start transferring on the given ACTIVE_ONLY TCS.
+ * @drv: The controller.
+ * @tcs_id: The global ID of this TCS.
+ */
static void __tcs_trigger(struct rsc_drv *drv, int tcs_id)
{
u32 enable;
@@ -372,6 +447,27 @@ static void __tcs_trigger(struct rsc_drv *drv, int tcs_id)
write_tcs_reg_sync(drv, RSC_DRV_CONTROL, tcs_id, 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).
+ *
+ * Only for use for ACTIVE_ONLY tcs_group, since those are the only ones
+ * that might be actively sending.
+ *
+ * This will walk through the TCSs 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.
+ *
+ * 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)
{
@@ -398,6 +494,14 @@ 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_ONLY.
+ * @tcs: A pointer to the ACTIVE_ONLY tcs_group.
+ *
+ * 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;
@@ -410,6 +514,20 @@ 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 of type ACTIVE_ONLY and writes the messages to it.
+ *
+ * If there are no free ACTIVE_ONLY TCSs 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;
@@ -422,11 +540,8 @@ static int tcs_write(struct rsc_drv *drv, const struct tcs_request *msg)
return PTR_ERR(tcs);

spin_lock_irqsave(&tcs->lock, flags);
+
spin_lock(&drv->lock);
- /*
- * The h/w does not like if we send a request to the same address,
- * when one is already in-flight or being processed.
- */
ret = check_for_req_inflight(drv, tcs, msg);
if (ret) {
spin_unlock(&drv->lock);
@@ -453,14 +568,23 @@ 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 one of the "ACTIVE_ONLY" tcs for
+ * ourselves--we don't try to share. If there are none available we'll
+ * wait indefinitely for a free one. It's important that we _aren't_ being
+ * called with IRQs disabled because of this (we might need the interrupt to
+ * fire to free up a busy TCS)
+ * - This function will not wait for the commands to be finished, only for
+ * that data to be programmed into the RPMh. See rpmh_tx_done() which will
+ * be called when the transfer is complete.
*
* 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)
{
@@ -484,6 +608,63 @@ int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
return ret;
}

+/**
+ * find_match() - Find if the cmd sequence is in the tcs_group
+ * @tcs: The tcs_group to search. Either sleep or wake.
+ * @cmd: The command sequence to search for; only addr is looked at.
+ * @len: The number of commands in the sequence.
+ *
+ * Searches through the given tcs_group to see if a given command sequence
+ * is in there.
+ *
+ * Two sequences are matches if they modify the same set of addresses in
+ * the same order. The value of the data is not considered when deciding if
+ * two things are matches.
+ *
+ * How this function works is best understood by example. For our example,
+ * we'll imagine our tcs group contains these (cmd, data) tuples:
+ * [(a, A), (b, B), (c, C), (d, D), (e, E), (f, F), (g, G), (h, H)]
+ * ...in other words it has an element where (addr=a, data=A), etc.
+ * ...we'll assume that there is one TCS in the group that can store 8 commands.
+ *
+ * - find_match([(a, X)]) => 0
+ * - find_match([(c, X), (d, X)]) => 2
+ * - find_match([(c, X), (d, X), (e, X)]) => 2
+ * - find_match([(z, X)]) => -ENODATA
+ * - find_match([(a, X), (y, X)]) => -EINVAL (and warning printed)
+ * - find_match([(g, X), (h, X), (i, X)]) => -EINVAL (and warning printed)
+ * - find_match([(y, X), (a, X)]) => -ENODATA
+ *
+ * NOTE: This function overall seems like it has questionable value.
+ * - It can be used to update a message in the TCS with new data, but I
+ * don't believe we actually do that--we always fully invalidate and
+ * re-write everything. Specifically it would be too limiting to force
+ * someone not to change the set of addresses written to each time.
+ * - This function could be attempting to avoid writing different data to
+ * the same address twice in a tcs_group. If that's the goal, it doesn't
+ * do a great job since find_match([(y, X), (a, X)]) return -ENODATA in my
+ * above example.
+ * - If you originally wrote [(a, A), (b, B), (c, C)] and later tried to
+ * write [(a, A), (b, B)] it'd look like a match and we wouldn't consider
+ * it an error that the size got shorter.
+ * - If two clients wrote sequences that happened to be placed in slots next
+ * to each other then a later check could match a sequence that was the
+ * size of both together.
+ *
+ * TODO: in light of the above, prehaps we can just remove this function?
+ * If we later come up with fancy algorithms for updating everything without
+ * full invalidations we can come up with something then.
+ *
+ * Only for use on sleep/wake TCSs since those are the only ones we maintain
+ * tcs->slots and tcs->cmd_cache for.
+ *
+ * Must be called with the tcs_lock for the group held.
+ *
+ * Return: If the given command sequence wasn't in the tcs_group: -ENODATA.
+ * If the given command sequence was in the tcs_group: the index of
+ * the slot in the tcs_group where the first command is.
+ * In some error cases (see above), -EINVAL.
+ */
static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
int len)
{
@@ -496,6 +677,11 @@ static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
if (i + len >= tcs->num_tcs * tcs->ncpt)
goto seq_err;
for (j = 0; j < len; j++) {
+ /*
+ * TODO: it's actually not valid to look at
+ * "cmd_cache[x]" if "slots[x]" doesn't have a bit
+ * set. Should add a check.
+ */
if (tcs->cmd_cache[i + j] != cmd[j].addr)
goto seq_err;
}
@@ -509,6 +695,23 @@ static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
return -EINVAL;
}

+/**
+ * find_slots() - Find a place to write the given message.
+ * @tcs: The controller.
+ * @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 TCSs since those are the only ones we maintain
+ * tcs->slots and tcs->cmd_cache 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)
{
@@ -520,7 +723,7 @@ static int find_slots(struct tcs_group *tcs, const struct tcs_request *msg,
if (slot >= 0)
goto copy_data;

- /* 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);
@@ -543,12 +746,13 @@ static int find_slots(struct tcs_group *tcs, const struct tcs_request *msg,
}

/**
- * rpmh_rsc_write_ctrl_data: Write request to the controller
- *
- * @drv: the controller
- * @msg: the data to be written 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.
*
* 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)
{
--
2.25.1.481.gfbce0eb801-goog
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