linux-kernel - Re: [PATCH v3] MMC/SDIO: enable SDIO device to suspend/resume asynchronously

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Date:	Mon, 16 Nov 2015 12:30:02 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Fu, Zhonghui" <zhonghui.fu@...ux.intel.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Neil Brown <neilb@...e.de>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Andreas Fenkart <afenkart@...il.com>,
	Joe Perches <joe@...ches.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] MMC/SDIO: enable SDIO device to suspend/resume asynchronously

On 15 November 2015 at 14:53, Fu, Zhonghui <zhonghui.fu@...ux.intel.com> wrote:
> Now, PM core supports asynchronous suspend/resume mode for devices
> during system suspend/resume, and the power state transition of one
> device may be completed in separate kernel thread. PM core ensures
> all power state transition timing dependency between devices. This
> patch enables SDIO card and function devices to suspend/resume
> asynchronously. This will take advantage of multicore and improve
> system suspend/resume speed. After enabling the SDIO devices and all
> their child devices to suspend/resume asynchronously on ASUS T100TA,
> the system suspend-to-idle time is reduced from 1645ms to 1119ms, and
> the system resume time is reduced from 940ms to 918ms.
>
> Signed-off-by: Zhonghui Fu <zhonghui.fu@...ux.intel.com>

I think this is an interesting change, but I wonder if you really
understand how this affects the order of how devices may be
suspended/resumed?

Also, I believe you didn't answer my question for the earlier version
of the patch, so let me try again.

There are a strict dependency chain when suspending/resuming devices
that must be maintained. Currently this is controlled via device
registration/probe order.

An SDIO func driver/device must always be suspended *before* the SDIO
card device. Additionally the corresponding MMC host, must be
suspended after the SDIO card device. Vice verse applies to the resume
sequence.

As this patch enables asynchronous suspend, I am worried that it will
break this dependency chain. What do you think?

Kind regards
Ulf Hansson

> ---
> Changes in v3:
> - Add test result in commit message
>
>  drivers/mmc/core/sdio.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
> index 16d838e..530ce88 100644
> --- a/drivers/mmc/core/sdio.c
> +++ b/drivers/mmc/core/sdio.c
> @@ -1113,6 +1113,8 @@ int mmc_attach_sdio(struct mmc_host *host)
>                 pm_runtime_enable(&card->dev);
>         }
>
> +       device_enable_async_suspend(&card->dev);
> +
>         /*
>          * The number of functions on the card is encoded inside
>          * the ocr.
> @@ -1133,6 +1135,8 @@ int mmc_attach_sdio(struct mmc_host *host)
>                  */
>                 if (host->caps & MMC_CAP_POWER_OFF_CARD)
>                         pm_runtime_enable(&card->sdio_func[i]->dev);
> +
> +               device_enable_async_suspend(&card->sdio_func[i]->dev);
>         }
>
>         /*
> -- 1.7.1
>
--
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