linux-kernel - Re: [PATCH v16 4/6] soc: qcom: rpmh: Invoke rpmh

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Date:   Thu, 09 Apr 2020 21:15:31 -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 v16 4/6] soc: qcom: rpmh: Invoke rpmh_flush() for dirty caches

Quoting Maulik Shah (2020-04-05 23:32:19)
> Add changes to invoke rpmh flush() from CPU PM notification.
> This is done when the last the cpu is entering power collapse and

'power collapse' is a qcom-ism. Maybe say something like "deep CPU idle
states"?

> controller is not busy.
> 
> Controllers that do have 'HW solver' mode do not need to register
> for CPU PM notification. They may be in autonomous mode executing
> low power mode and do not require rpmh_flush() to happen from CPU
> PM notification.

Can you provide an example of a HW solver mode controller? Presumably
the display RSC is one of these?

> 
> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>

> diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> index b718221..fbe1f3e 100644
> --- a/drivers/soc/qcom/rpmh-rsc.c
> +++ b/drivers/soc/qcom/rpmh-rsc.c
> @@ -521,8 +527,86 @@ int rpmh_rsc_write_ctrl_data(struct rsc_drv *drv, const struct tcs_request *msg)
>         return tcs_ctrl_write(drv, msg);
>  }
>  
> +/**
> + * rpmh_rsc_ctrlr_is_busy() - Check if any of the AMCs are busy.
> + *
> + * @drv: The controller
> + *
> + * Checks if any of the AMCs are busy in handling ACTIVE sets.
> + * This is called from the last cpu powering down before flushing
> + * SLEEP and WAKE sets. If AMCs are busy, controller can not enter
> + * power collapse, so deny from the last cpu's pm notification.
> + *
> + * Return:
> + * * False             - AMCs are idle
> + * * True              - AMCs are busy
> + */
> +static bool rpmh_rsc_ctrlr_is_busy(struct rsc_drv *drv)

Can drv be const? Would be nice to make it const in some places in this
driver.

> +{
> +       int m;
> +       struct tcs_group *tcs = get_tcs_of_type(drv, ACTIVE_TCS);
> +
> +       /*
> +        * If we made an active request on a RSC that does not have a
> +        * dedicated TCS for active state use, then re-purposed wake TCSes
> +        * should be checked for not busy.

not busy, because we use wake TCSes for active requests in this case.

> +        *
> +        * Since this is called from the last cpu, need not take drv or tcs
> +        * lock before checking tcs_is_free().
> +        */
> +       if (!tcs->num_tcs)
> +               tcs = get_tcs_of_type(drv, WAKE_TCS);
> +
> +       for (m = tcs->offset; m < tcs->offset + tcs->num_tcs; m++) {
> +               if (!tcs_is_free(drv, m))
> +                       return true;
> +       }
> +
> +       return false;
> +}
[...]
> +
> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> index a75f3df..88f8801 100644
> --- a/drivers/soc/qcom/rpmh.c
> +++ b/drivers/soc/qcom/rpmh.c
> @@ -433,16 +430,17 @@ static int send_single(struct rpmh_ctrlr *ctrlr, enum rpmh_state state,
>  }
>  
>  /**
> - * rpmh_flush: Flushes the buffered active and sleep sets to TCS
> + * rpmh_flush() - Flushes the buffered sleep and wake sets to TCSes
>   *
> - * @ctrlr: controller making request to flush cached data
> + * @ctrlr: Controller making request to flush cached data
>   *
> - * Return: -EBUSY if the controller is busy, probably waiting on a response
> - * to a RPMH request sent earlier.
> + * This function is called from sleep code on the last CPU
> + * (thus no spinlock needed).

Might be good to stick a lockdep_assert_irqs_disabled() in this function
then. That would document that this function should only be called when
irqs are disabled.

>   *
> - * This function is always called from the sleep code from the last CPU
> - * that is powering down the entire system. Since no other RPMH API would be
> - * executing at this time, it is safe to run lockless.
> + * Return:
> + * * 0          - Success
> + * * -EAGAIN    - Retry again
> + * * Error code - Otherwise
>   */
>  int rpmh_flush(struct rpmh_ctrlr *ctrlr)

This function name keeps throwing me off. Can we please call it
something like rpmh_configure_tcs_sleep_wake()? The word "flush" seems
to imply there's some sort of cache going on, but that's not really the
case. We're programming a couple TCS FIFOs so that they can be used
across deep CPU sleep states.

>  {
> @@ -455,9 +453,7 @@ int rpmh_flush(struct rpmh_ctrlr *ctrlr)
>         }
>  
>         /* Invalidate the TCSes first to avoid stale data */
> -       do {
> -               ret = rpmh_rsc_invalidate(ctrlr_to_drv(ctrlr));
> -       } while (ret == -EAGAIN);
> +       ret = rpmh_rsc_invalidate(ctrlr_to_drv(ctrlr));
>         if (ret)
>                 return ret;
>