Re: [PATCH] mmc: core: Enable runtime PM management of host devices

[Konstantin Dorfman <kdorfman@codeaurora.org>]

On 03/27/2015 02:15 PM, Ulf Hansson wrote:
> Currently those host drivers which have deployed runtime PM, deals with
> the runtime PM reference counting entirely by themselves.
>
> Since host drivers don't know when the core will send the next request
> through some of the host_ops callbacks, they need to handle runtime PM
> get/put between each an every request.
>
> In quite many cases this has some negative effects, since it leads to a
> high frequency of scheduled runtime PM suspend operations. That due to
> the runtime PM reference count will normally reach zero in-between
> every request.
>
> We can decrease that frequency, by enabling the core to deal with
> runtime PM reference counting of the host device. Since the core often
> knows that it will send a seqeunce of requests, it makes sense for it
> to keep a runtime PM reference count during these periods.
>
> More exactly, let's increase the runtime PM reference count by invoking
> pm_runtime_get_sync() from __mmc_claim_host(). Restore that action by
> invoking pm_runtime_mark_last_busy() and pm_runtime_put_autosuspend()
> in mmc_release_host(). In this way a runtime PM reference count will be
> kept during the complete cycle of a claim -> release host.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>   drivers/mmc/core/core.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 709ada9..c296bc0 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -897,6 +897,7 @@ int __mmc_claim_host(struct mmc_host *host, atomic_t *abort)
>   	DECLARE_WAITQUEUE(wait, current);
>   	unsigned long flags;
>   	int stop;
> +	bool pm = false;
>
>   	might_sleep();
>
> @@ -916,13 +917,18 @@ int __mmc_claim_host(struct mmc_host *host, atomic_t *abort)
>   		host->claimed = 1;
>   		host->claimer = current;
>   		host->claim_cnt += 1;
> +		if (host->claim_cnt == 1)
> +			pm = true;
>   	} else
>   		wake_up(&host->wq);
>   	spin_unlock_irqrestore(&host->lock, flags);
>   	remove_wait_queue(&host->wq, &wait);
> +
> +	if (pm)
> +		pm_runtime_get_sync(mmc_dev(host));
> +
>   	return stop;
>   }
> -
>   EXPORT_SYMBOL(__mmc_claim_host);
>
>   /**
> @@ -947,6 +953,8 @@ void mmc_release_host(struct mmc_host *host)
>   		host->claimer = NULL;
>   		spin_unlock_irqrestore(&host->lock, flags);
>   		wake_up(&host->wq);
> +		pm_runtime_mark_last_busy(mmc_dev(host));
> +		pm_runtime_put_autosuspend(mmc_dev(host));
>   	}
>   }
>   EXPORT_SYMBOL(mmc_release_host);
>
Acked-by: Konstantin Dorfman <kdorfman@codeaurora.org>

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