Re: [PATCH v2 3/6] drivers: qcom: rpmh: disallow active requests in solver mode

[Matthias Kaehlcke <mka@chromium.org>]

Hi Raju/Lina,

On Fri, Jul 27, 2018 at 03:34:46PM +0530, Raju P L S S S N wrote:
> From: Lina Iyer <ilina@codeaurora.org>
> 
> Controllers may be in 'solver' state, where they could be in autonomous
> mode executing low power modes for their hardware and as such are not
> available for sending active votes. Device driver may notify RPMH API
> that the controller is in solver mode and when in such mode, disallow
> requests from platform drivers for state change using the RSC.
> 
> Signed-off-by: Lina Iyer <ilina@codeaurora.org>
> Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>
> ---
>  drivers/soc/qcom/rpmh-internal.h |  2 ++
>  drivers/soc/qcom/rpmh.c          | 59 ++++++++++++++++++++++++++++++++++++++++
>  include/soc/qcom/rpmh.h          |  5 ++++
>  3 files changed, 66 insertions(+)
> 
> diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
> index 4ff43bf..6cd2f78 100644
> --- a/drivers/soc/qcom/rpmh-internal.h
> +++ b/drivers/soc/qcom/rpmh-internal.h
> @@ -72,12 +72,14 @@ struct rpmh_request {
>   * @cache_lock: synchronize access to the cache data
>   * @dirty: was the cache updated since flush
>   * @batch_cache: Cache sleep and wake requests sent as batch
> + * @in_solver_mode: Controller is busy in solver mode
>   */
>  struct rpmh_ctrlr {
>  	struct list_head cache;
>  	spinlock_t cache_lock;
>  	bool dirty;
>  	struct list_head batch_cache;
> +	bool in_solver_mode;
>  };
>  
>  /**
> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
> index 2382276..0d276fd 100644
> --- a/drivers/soc/qcom/rpmh.c
> +++ b/drivers/soc/qcom/rpmh.c
> @@ -5,6 +5,7 @@
>  
>  #include <linux/atomic.h>
>  #include <linux/bug.h>
> +#include <linux/delay.h>
>  #include <linux/interrupt.h>
>  #include <linux/jiffies.h>
>  #include <linux/kernel.h>
> @@ -75,6 +76,50 @@ static struct rpmh_ctrlr *get_rpmh_ctrlr(const struct device *dev)
>  	return &drv->client;
>  }
>  
> +static int check_ctrlr_state(struct rpmh_ctrlr *ctrlr, enum rpmh_state state)
> +{
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	/* Do not allow setting active votes when in solver mode */
> +	spin_lock_irqsave(&ctrlr->cache_lock, flags);
> +	if (ctrlr->in_solver_mode && state == RPMH_ACTIVE_ONLY_STATE)
> +		ret = -EBUSY;
> +	spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
> +
> +	return ret;
> +}
> +
> +/**
> + * rpmh_mode_solver_set: Indicate that the RSC controller hardware has
> + * been configured to be in solver mode
> + *
> + * @dev: the device making the request
> + * @enable: Boolean value indicating if the controller is in solver mode.
> + *
> + * When solver mode is enabled, passthru API will not be able to send wake
> + * votes, just awake and active votes.
> + */
> +int rpmh_mode_solver_set(const struct device *dev, bool enable)
> +{
> +	struct rpmh_ctrlr *ctrlr = get_rpmh_ctrlr(dev);
> +	unsigned long flags;
> +
> +	for (;;) {
> +		spin_lock_irqsave(&ctrlr->cache_lock, flags);
> +		if (rpmh_rsc_ctrlr_is_idle(ctrlr_to_drv(ctrlr))) {
> +			ctrlr->in_solver_mode = enable;

As commented on '[v2,1/6] drivers: qcom: rpmh-rsc: return if the
controller is idle', this seems potentially
racy. _is_idle() could report the controller as idle, even though some
TCSes are in use (after _is_idle() visited them).

Additional locking may be needed or a comment if this situation should
never happen on a sane system (I don't know enough about RPMh and its
clients to judge if this is the case).