Re: [PATCH v2 09/10] drivers: qcom: rpmh: add support for batch RPMH request

[Lina Iyer]

On Wed, Feb 21 2018 at 23:25 +0000, Evan Green wrote:
> Hello Lina,
>
> On Thu, Feb 15, 2018 at 9:35 AM, Lina Iyer <ilina@xxxxxxxxxxxxxx> wrote:
> > Platform drivers need make a lot of resource state requests at the same
> > time, say, at the start or end of an usecase. It can be quite
> > inefficient to send each request separately. Instead they can give the
> > RPMH library a batch of requests to be sent and wait on the whole
> > transaction to be complete.
> >
> > rpmh_write_batch() is a blocking call that can be used to send multiple
> > RPMH command sets. Each RPMH command set is set asynchronously and the
> > API blocks until all the command sets are complete and receive their
> > tx_done callbacks.
> >
> > Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> > ---
> >  drivers/soc/qcom/rpmh.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/soc/qcom/rpmh.h |   8 +++
> >  2 files changed, 158 insertions(+)
> >
> > diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> > index dff4c46be3af..6f60bb9a4dfa 100644
> > --- a/drivers/soc/qcom/rpmh.c
> > +++ b/drivers/soc/qcom/rpmh.c
> [...]
> > @@ -394,6 +537,11 @@ int rpmh_flush(struct rpmh_client *rc)
> >         }
> >         spin_unlock_irqrestore(&rpm->lock, flags);
> >
> > +       /* First flush the cached batch requests */
> > +       ret = flush_batch(rc);
> > +       if (ret)
> > +               return ret;
> > +
> >         /*
> >          * Nobody else should be calling this function other than system PM,,
> >          * hence we can run without locks.
This comment and the comment in the header of this function.

> > @@ -438,6 +586,8 @@ int rpmh_invalidate(struct rpmh_client *rc)
> >         if (IS_ERR_OR_NULL(rc))
> >                 return -EINVAL;
> >
> > +       invalidate_batch(rc);
> > +
>
> Similarly to my comments in patch 7, aren't there races here with
> adding new elements? After flush_batch, but before invalidate_batch,
> somebody could call cache_batch, which would add new things on the end
> of the array. These new items would be clobbered by invalidate_batch,
> without having been flushed first.
Flush is a system PM function and is not called by drivers and is not
expected to run conncurrently with other threads using the RPMH library.

Thanks,
Lina