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Subject[PATCH v3 05/10] drivers: qcom: rpmh-rsc: Kill cmd_cache and find_match() with fire
Date
The "cmd_cache" in RPMH wasn't terribly sensible.  Specifically:

- The current code doesn't realy detect "conflicts" properly any case
where the sequence being checked has more than one entry. One
simple way to see this in the current code is that if cmd[0].addr
isn't found that cmd[1].addr is never checked.
- The code attempted to use the "cmd_cache" to update an existing
message in a sleep/wake TCS with new data. The goal appeared to be
to update part of a TCS while leaving the rest of the TCS alone. We
never actually do this. We always fully invalidate and re-write
everything.
- If/when we try to optimize things to not fully invalidate / re-write
every time we update the TCSes we'll need to think it through very
carefully. Specifically requirement of find_match() that the new
sequence of addrs must match exactly the old sequence of addrs seems
inflexible. It's also not documented in rpmh_write() and
rpmh_write_batch(). In any case, if we do decide to require updates
to keep the exact same sequence and length then presumably the API
and data structures should be updated to understand groups more
properly. The current algorithm doesn't really keep track of the
length of the old sequence and there are several boundary-condition
bugs because of that. Said another way: if we decide to do
something like this in the future we should start from scratch and
thus find_match() isn't useful to keep around.

This patch isn't quite a no-op. Specifically:

- It should be a slight performance boost of not searching through so
many arrays.
- The old code would have done something useful in one case: it would
allow someone calling rpmh_write() to override the data that came
from rpmh_write_batch(). I don't believe that actually happens in
reality.

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

Changes in v3:
- Kill find_match moves from patch #9 to patch #5 (Maulik).
- Rewrote commit message to adjust for patch order.

Changes in v2:
- Got rid of useless "if (x) continue" at end of for loop.

drivers/soc/qcom/rpmh-internal.h | 2 --
drivers/soc/qcom/rpmh-rsc.c | 47 --------------------------------
2 files changed, 49 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
index e9a90cb7773e..6a6d776ccca9 100644
--- a/drivers/soc/qcom/rpmh-internal.h
+++ b/drivers/soc/qcom/rpmh-internal.h
@@ -30,7 +30,6 @@ struct rsc_drv;
* @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
*/
struct tcs_group {
@@ -42,7 +41,6 @@ struct tcs_group {
int ncpt;
spinlock_t lock;
const struct tcs_request *req[MAX_TCS_PER_TYPE];
- u32 *cmd_cache;
DECLARE_BITMAP(slots, MAX_TCS_SLOTS);
};

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 855a1dab7718..da1045c92b38 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -522,42 +522,12 @@ int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg)
return ret;
}

-static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
- int len)
-{
- int i, j;
-
- /* Check for already cached commands */
- for_each_set_bit(i, tcs->slots, MAX_TCS_SLOTS) {
- if (tcs->cmd_cache[i] != cmd[0].addr)
- continue;
- if (i + len >= tcs->num_tcs * tcs->ncpt)
- goto seq_err;
- for (j = 0; j < len; j++) {
- if (tcs->cmd_cache[i + j] != cmd[j].addr)
- goto seq_err;
- }
- return i;
- }
-
- return -ENODATA;
-
-seq_err:
- WARN(1, "Message does not match previous sequence.\n");
- return -EINVAL;
-}
-
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;

- /* Find if we already have the msg in our TCS */
- slot = find_match(tcs, msg->cmds, msg->num_cmds);
- if (slot >= 0)
- goto copy_data;
-
/* Do over, until we can fit the full payload in a TCS */
do {
slot = bitmap_find_next_zero_area(tcs->slots, MAX_TCS_SLOTS,
@@ -567,11 +537,7 @@ static int find_slots(struct tcs_group *tcs, const struct tcs_request *msg,
i += tcs->ncpt;
} while (slot + msg->num_cmds - 1 >= i);

-copy_data:
bitmap_set(tcs->slots, slot, msg->num_cmds);
- /* Copy the addresses of the resources over to the slots */
- for (i = 0; i < msg->num_cmds; i++)
- tcs->cmd_cache[slot + i] = msg->cmds[i].addr;

offset = slot / tcs->ncpt;
*tcs_id = offset + tcs->offset;
@@ -763,19 +729,6 @@ static int rpmh_probe_tcs_config(struct platform_device *pdev,
tcs->mask = ((1 << tcs->num_tcs) - 1) << st;
tcs->offset = st;
st += tcs->num_tcs;
-
- /*
- * Allocate memory to cache sleep and wake requests to
- * avoid reading TCS register memory.
- */
- if (tcs->type == ACTIVE_TCS)
- continue;
-
- tcs->cmd_cache = devm_kcalloc(&pdev->dev,
- tcs->num_tcs * ncpt, sizeof(u32),
- GFP_KERNEL);
- if (!tcs->cmd_cache)
- return -ENOMEM;
}

drv->num_tcs = st;
--
2.26.0.292.g33ef6b2f38-goog
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