Re: [PATCH v2] mmc: core: Remove redundant rescan_disable flag

[Adrian Hunter <adrian.hunter@intel.com>]

On 28/04/2016 9:29 p.m., Ulf Hansson wrote:
> For the reasons explained below, it's safe to remove the rescan_disable
> flag.
>
> 1)
> cancel_delayed_work_sync() prevents an executing work from re-scheduling
> itself.
>
> 2)
> We are using the system_freezable_wq for the rescan works. As that queue
> becomes frozen when userspace becomes frozen during system PM, we don't
> need to disable the rescan works in the PM_SUSPEND_PREPARE phase.

What about the case when a SDIO card has to be removed?  Seems like a rescan
could theoretically get scheduled and run before the workqueue is frozen.

>
> 3)
> At host registration it's not safe to schedule a detect work until
> mmc_start_host() is invoked. Trying to use the rescan_disable flag to
> prevent a rescan work from being executed isn't helping.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>
> Changes in v2:
> 	Updated changelog to better reflect why rescan_flag is redundant.
>
> ---
>   drivers/mmc/core/core.c  | 12 ------------
>   drivers/mmc/core/host.c  |  3 ---
>   include/linux/mmc/host.h |  1 -
>   3 files changed, 16 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 99275e4..b8c6a11 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2580,9 +2580,6 @@ void mmc_rescan(struct work_struct *work)
>   		container_of(work, struct mmc_host, detect.work);
>   	int i;
>
> -	if (host->rescan_disable)
> -		return;
> -
>   	/* If there is a non-removable card registered, only scan once */
>   	if (!mmc_card_is_removable(host) && host->rescan_entered)
>   		return;
> @@ -2649,7 +2646,6 @@ void mmc_rescan(struct work_struct *work)
>   void mmc_start_host(struct mmc_host *host)
>   {
>   	host->f_init = max(freqs[0], host->f_min);
> -	host->rescan_disable = 0;
>   	host->ios.power_mode = MMC_POWER_UNDEFINED;
>
>   	mmc_claim_host(host);
> @@ -2674,7 +2670,6 @@ void mmc_stop_host(struct mmc_host *host)
>   	if (host->slot.cd_irq >= 0)
>   		disable_irq(host->slot.cd_irq);
>
> -	host->rescan_disable = 1;
>   	cancel_delayed_work_sync(&host->detect);
>
>   	/* clear pm flags now and let card drivers set them as needed */
> @@ -2788,9 +2783,6 @@ static int mmc_pm_notify(struct notifier_block *notify_block,
>   	case PM_HIBERNATION_PREPARE:
>   	case PM_SUSPEND_PREPARE:
>   	case PM_RESTORE_PREPARE:
> -		spin_lock_irqsave(&host->lock, flags);
> -		host->rescan_disable = 1;
> -		spin_unlock_irqrestore(&host->lock, flags);
>   		cancel_delayed_work_sync(&host->detect);
>
>   		if (!host->bus_ops)
> @@ -2814,10 +2806,6 @@ static int mmc_pm_notify(struct notifier_block *notify_block,
>   	case PM_POST_SUSPEND:
>   	case PM_POST_HIBERNATION:
>   	case PM_POST_RESTORE:
> -
> -		spin_lock_irqsave(&host->lock, flags);
> -		host->rescan_disable = 0;
> -		spin_unlock_irqrestore(&host->lock, flags);
>   		_mmc_detect_change(host, 0, false);
>
>   	}
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index e0a3ee1..e972489 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -319,9 +319,6 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
>   	if (!host)
>   		return NULL;
>
> -	/* scanning will be enabled when we're ready */
> -	host->rescan_disable = 1;
> -
>   again:
>   	if (!ida_pre_get(&mmc_host_ida, GFP_KERNEL)) {
>   		kfree(host);
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 85800b4..7fbe5c0 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -330,7 +330,6 @@ struct mmc_host {
>   	unsigned int		doing_retune:1;	/* re-tuning in progress */
>   	unsigned int		retune_now:1;	/* do re-tuning at next req */
>
> -	int			rescan_disable;	/* disable card detection */
>   	int			rescan_entered;	/* used with nonremovable devices */
>
>   	int			need_retune;	/* re-tuning is needed */
>