Re: [PATCH v17 2/6] soc: qcom: rpmh: Update dirty flag only when data changes

From: Doug Anderson
Date: Fri Apr 17 2020 - 17:17:10 EST


On Thu, Apr 16, 2020 at 4:59 PM Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
>
> Quoting Maulik Shah (2020-04-12 07:50:00)
> > diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> > index eb0ded0..03630ae 100644
> > --- a/drivers/soc/qcom/rpmh.c
> > +++ b/drivers/soc/qcom/rpmh.c
> > @@ -133,26 +134,27 @@ 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);
> > list_add_tail(&req->list, &ctrlr->cache);
> >
> > existing:
> > + old_sleep_val = req->sleep_val;
> > + old_wake_val = req->wake_val;
> > +
> > switch (state) {
> > case RPMH_ACTIVE_ONLY_STATE:
> > - if (req->sleep_val != UINT_MAX)
> > - req->wake_val = cmd->data;
> > - break;
> > case RPMH_WAKE_ONLY_STATE:
> > req->wake_val = cmd->data;
> > break;
> > case RPMH_SLEEP_STATE:
> > req->sleep_val = cmd->data;
> > break;
> > - default:
> > - break;
> > }
> >
> > - ctrlr->dirty = true;
> > + ctrlr->dirty = (req->sleep_val != old_sleep_val ||
> > + req->wake_val != old_wake_val) &&
> > + req->sleep_val != UINT_MAX &&
> > + req->wake_val != UINT_MAX;
>
> Can this change ctrl->dirty from true to false? I'm worried that we need
> to make this a saturating assignment instead of an assignment.
>
> ctrl->dirty = ctrl->dirty || (req->sleep_val != .. );

This seems like a serious problem with the current code and feels like
we need a fix sooner rather than later. I'm sorry I missed it in
review (and in fact, I probably suggested the exact code that's here
so it's even more my fault). :(

I posted:

20200417141531.1.Ia4b74158497213eabad7c3d474c50bfccb3f342e@changeid">https://lore.kernel.org/r/20200417141531.1.Ia4b74158497213eabad7c3d474c50bfccb3f342e@changeid

-Doug