linux-kernel - Re: [PATCH 3/7] scsi: Drop runtime PM usage count after host is added

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Message-ID: <CAGRGNgUzUDWQ3jDfUuaf8x4G_zsZYe1p2=e_kDR4FkcMp5bUvg@mail.gmail.com>
Date:	Fri, 19 Feb 2016 09:50:50 +1100
From:	Julian Calaby <julian.calaby@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Tejun Heo <tj@...nel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH 3/7] scsi: Drop runtime PM usage count after host is added

Hi Mika,

On Thu, Feb 18, 2016 at 7:54 PM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> Runtime PM of the SCSI host is already handled by calls to
> scsi_autopm_get_host() and scsi_autopm_put_host() from appropriate places
> whenever the host needs to be powered on. This works fine when there is
> device connected to the host as once it runtime suspends the host will too.
>
> However, if there is no device connected the host is never runtime
> suspended (the usage counter is always 0).
>
> Allow runtime suspend of host even if it has no devices connected by
> calling scsi_autopm_put_host() at the end of scsi_add_host_with_dma(). We
> temporarily increase runtime PM usage counter first so call to
> scsi_autopm_put_host() will result idle request to be scheduled for the
> device.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
>  drivers/scsi/hosts.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 82ac1cd818ac..e46bf4d152a0 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -250,6 +250,12 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>         if (error)
>                 goto out_destroy_freelist;
>
> +       /*
> +        * Increase usage count temporarily here so that calling
> +        * scsi_autopm_put_host() will trigger runtime idle if there is
> +        * nothing else preventing suspending the device.
> +        */
> +       pm_runtime_get_noresume(&shost->shost_gendev);
>         pm_runtime_set_active(&shost->shost_gendev);
>         pm_runtime_enable(&shost->shost_gendev);
>         device_enable_async_suspend(&shost->shost_gendev);
> @@ -290,6 +296,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>                 goto out_destroy_host;
>
>         scsi_proc_host_add(shost);
> +       scsi_autopm_put_host(shost);

Would it be cleaner to export the code that runs when the usage
counter decrements and call it here?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/