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

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Message-ID: <158708153779.132238.7823999141480422982@swboyd.mtv.corp.google.com>
Date:   Thu, 16 Apr 2020 16:58:57 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Maulik Shah <mkshah@...eaurora.org>, bjorn.andersson@...aro.org,
        dianders@...omium.org, evgreen@...omium.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        agross@...nel.org, mka@...omium.org, rnayak@...eaurora.org,
        ilina@...eaurora.org, lsrao@...eaurora.org,
        Maulik Shah <mkshah@...eaurora.org>
Subject: Re: [PATCH v17 2/6] soc: qcom: rpmh: Update dirty flag only when data changes

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 != .. );

> +
>  unlock:
>         spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
>