Re: [PATCH v8 2/3] soc: qcom: rpmh: Update dirty flag only when data changes

[Maulik Shah]

On 2/27/2020 11:48 PM, Evan Green wrote:
> On Thu, Feb 27, 2020 at 12:57 AM Maulik Shah <mkshah@xxxxxxxxxxxxxx> wrote:
> > Currently rpmh ctrlr dirty flag is set for all cases regardless of data
> > is really changed or not. Add changes to update dirty flag when data is
> > changed to newer values.
> >
> > Also move dirty flag updates to happen from within cache_lock and remove
> > unnecessary INIT_LIST_HEAD() call and a default case from switch.
> >
> > Fixes: 600513dfeef3 ("drivers: qcom: rpmh: cache sleep/wake state requests")
> > Signed-off-by: Maulik Shah <mkshah@xxxxxxxxxxxxxx>
> > Reviewed-by: Srinivas Rao L <lsrao@xxxxxxxxxxxxxx>
> > ---
> >   drivers/soc/qcom/rpmh.c | 29 ++++++++++++++++-------------
> >   1 file changed, 16 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> > index eb0ded0..3f5d9eb 100644
> > --- a/drivers/soc/qcom/rpmh.c
> > +++ b/drivers/soc/qcom/rpmh.c
> > @@ -133,26 +133,30 @@ static struct cache_req *cache_rpm_request(struct rpmh_ctrlr *ctrlr,
> >
> >          req->addr = cmd->addr;
> >          req->sleep_val = req->wake_val = UINT_MAX;
> > -       INIT_LIST_HEAD(&req->list);
> Thanks!
>
> >          list_add_tail(&req->list, &ctrlr->cache);
> >
> >   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;
> > -               break;
> > -       default:
> > +               if (req->sleep_val != cmd->data) {
> > +                       req->sleep_val = cmd->data;
> > +                       ctrlr->dirty = true;
> > +               }
> >                  break;
> >          }
> >
> > -       ctrlr->dirty = true;
> >   unlock:
> >          spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
> >
> > @@ -287,6 +291,7 @@ static void cache_batch(struct rpmh_ctrlr *ctrlr, struct batch_cache_req *req)
> >
> >          spin_lock_irqsave(&ctrlr->cache_lock, flags);
> >          list_add_tail(&req->list, &ctrlr->batch_cache);
> > +       ctrlr->dirty = true;
> >          spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
> >   }
> >
> > @@ -323,6 +328,7 @@ 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);
> >   }
> >
> > @@ -456,13 +462,9 @@ 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) {
> > -               pr_debug("Skipping flush, TCS has latest data.\n");
> > -               return 0;
> > -       }
> > -
> >          /* First flush the cached batch requests */
> >          ret = flush_batch(ctrlr);
> >          if (ret)
> > @@ -488,7 +490,9 @@ 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);
> You're acquiring a lock around an operation that's already inherently
> atomic, which is not right. If the comment earlier in this function is
> still correct that "Nobody else should be calling this function other
> than system PM, hence we can run without locks", then you can simply
> remove this hunk and the part moving ->dirty = true into
> invalidate_batch.
>
> However, if rpmh_flush() can now be called in a scenario where
> pre-emption is enabled or multiple cores are alive, then ctrlr->cache
> is no longer adequately protected. You'd need to add a lock
> acquire/release around the list iteration above, and fix up the
> comment.
> -Evan

Hi Evan,

Right, rpmh_flush() now can be called from any cpu. i will remove 
comments from above.

part for rpmh_flush(), flush_batch() and ctrlr->dirty update was 
already covered within cache lock, however its needed to protect

entire rpmh_flush() in cache_lock now.

updates in v9.

Thanks,

Maulik

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