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SubjectRe: [PATCH v7 2/3] soc: qcom: rpmh: Update dirty flag only when data changes
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Quoting Maulik Shah (2020-02-25 21:27:12)
> Currently rpmh ctrlr dirty flag is set for all cases regardless
> of data is really changed or not. Add changes to update it when
> data is updated to newer values.
>
> Also move dirty flag updates to happen from within cache_lock.
>
> Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
> Reviewed-by: Srinivas Rao L <lsrao@codeaurora.org>

Probably worth adding a Fixes tag here? Doesn't make sense to mark
something dirty when it isn't changed.

> ---
> drivers/soc/qcom/rpmh.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> index eb0ded0..83ba4e0 100644
> --- a/drivers/soc/qcom/rpmh.c
> +++ b/drivers/soc/qcom/rpmh.c
> @@ -139,20 +139,27 @@ static struct cache_req *cache_rpm_request(struct rpmh_ctrlr *ctrlr,
> existing:
> switch (state) {
> case RPMH_ACTIVE_ONLY_STATE:
> - if (req->sleep_val != UINT_MAX)
> + if (req->sleep_val != UINT_MAX) {
> req->wake_val = cmd->data;
> + ctrlr->dirty = true;
> + }
> break;
> case RPMH_WAKE_ONLY_STATE:
> - req->wake_val = cmd->data;
> + if (req->wake_val != cmd->data) {
> + req->wake_val = cmd->data;
> + ctrlr->dirty = true;
> + }
> break;
> case RPMH_SLEEP_STATE:
> - req->sleep_val = cmd->data;
> + if (req->sleep_val != cmd->data) {
> + req->sleep_val = cmd->data;
> + ctrlr->dirty = true;
> + }
> break;
> default:
> break;

Please remove the default case. There are only three states in the enum. The
compiler will warn if a switch statement doesn't cover all cases and
we'll know to add something here if another enum value is added in the
future.

> }
>
> - ctrlr->dirty = true;
> unlock:
> spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
>
> @@ -323,6 +331,7 @@ static void invalidate_batch(struct rpmh_ctrlr *ctrlr)
> list_for_each_entry_safe(req, tmp, &ctrlr->batch_cache, list)
> kfree(req);
> INIT_LIST_HEAD(&ctrlr->batch_cache);
> + ctrlr->dirty = true;
> spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
> }
>
> @@ -456,6 +465,7 @@ static int send_single(struct rpmh_ctrlr *ctrlr, enum rpmh_state state,
> int rpmh_flush(struct rpmh_ctrlr *ctrlr)
> {
> struct cache_req *p;
> + unsigned long flags;
> int ret;
>
> if (!ctrlr->dirty) {
> @@ -488,7 +498,9 @@ int rpmh_flush(struct rpmh_ctrlr *ctrlr)
> return ret;
> }
>
> + spin_lock_irqsave(&ctrlr->cache_lock, flags);
> ctrlr->dirty = false;
> + spin_unlock_irqrestore(&ctrlr->cache_lock, flags);

So we take the spinlock to update it here. But we don't hold the
spinlock to test for !dirty up above. Seems like either rpmh_flush() can
only be called sequentially, or the lock added here needs to be held
during the whole flush. Which way is it?

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