Re: [PATCH v7 2/3] soc: qcom: rpmh: Update dirty flag only when data changes

[Maulik Shah]

On 2/27/2020 4:13 AM, Stephen Boyd wrote:
> 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@xxxxxxxxxxxxxx>
> > Reviewed-by: Srinivas Rao L <lsrao@xxxxxxxxxxxxxx>
> Probably worth adding a Fixes tag here? Doesn't make sense to mark
> something dirty when it isn't changed.
Done. will update in v8.
> > ---
> >   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.
Done.
> >          }
> >   
> > -       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?

Thanks, i will remove !ctrlr->dirty check within rpmh_flush() as 
currently we invoke it only when caches are dirty.

Last cpu going down can first check dirty flag outside rpmh_flush() and 
decide to invoke it accoringly.

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