linux-kernel - Re: [PATCH 08/11] mmc: core: Fixup processing of SDIO IRQs during system suspend/resume

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Date:   Thu, 5 Sep 2019 16:48:10 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Linux MMC List <linux-mmc@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Yong Mao <yong.mao@...iatek.com>,
        Chaotian Jing <chaotian.jing@...iatek.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/11] mmc: core: Fixup processing of SDIO IRQs during
 system suspend/resume

Hi,

On Tue, Sep 3, 2019 at 7:22 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> System suspend/resume of SDIO cards, with SDIO IRQs enabled and when using
> MMC_CAP2_SDIO_IRQ_NOTHREAD is unfortunate still suffering from a fragile
> behaviour. Some problems have been taken care of so far, but more issues
> remains.
>
> For example, calling the ->ack_sdio_irq() callback to let host drivers
> re-enable the SDIO IRQs is a bad idea, unless the IRQ have been consumed,
> which may not be the case during system suspend/resume. This may lead to
> that a host driver re-signals the same SDIO IRQ over and over again,
> causing a storm of IRQs and gives a ping-pong effect towards the
> sdio_irq_work().
>
> Moreover, calling the ->enable_sdio_irq() callback at system resume to
> re-enable already enabled SDIO IRQs for the host, causes the runtime PM
> count for some host drivers to become in-balanced. This then leads to the
> host to remain runtime resumed, no matter if it's needed or not.
>
> To fix these problems, let's check if process_sdio_pending_irqs() actually
> consumed the SDIO IRQ, before we continue to ack the IRQ by invoking the
> ->ack_sdio_irq() callback.
>
> Additionally, there should be no need to re-enable SDIO IRQs as the host
> driver already knows if they were enabled at system suspend, thus also
> whether it needs to re-enable them at system resume. For this reason, drop
> the call to ->enable_sdio_irq() during system resume.
>
> In regards to these changes there is yet another issue, which is when there
> is an SDIO IRQ being signaled by the host driver, but after the SDIO card
> has been system suspended. Currently these IRQs are just thrown away, while
> we should at least make sure to try to consume them when the SDIO card has
> been system resumed. Fix this by calling sdio_signal_irq() after system
> resumed the SDIO card.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>  drivers/mmc/core/sdio.c     | 2 +-
>  drivers/mmc/core/sdio_irq.c | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
> index c557f1519b77..3114d496495a 100644
> --- a/drivers/mmc/core/sdio.c
> +++ b/drivers/mmc/core/sdio.c
> @@ -1015,7 +1015,7 @@ static int mmc_sdio_resume(struct mmc_host *host)
>                 if (!(host->caps2 & MMC_CAP2_SDIO_IRQ_NOTHREAD))
>                         wake_up_process(host->sdio_irq_thread);
>                 else if (host->caps & MMC_CAP_SDIO_IRQ)
> -                       host->ops->enable_sdio_irq(host, 1);
> +                       sdio_signal_irq(host);

Is this always safe?  On 1-function cards you won't poll CCCR_INTx so
you'll always signal an interrupt at resume time, won't you?

-Doug