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

[Matthias Kaehlcke <mka@chromium.org>]

On Tue, Sep 03, 2019 at 04:22:04PM +0200, Ulf Hansson 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@linaro.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);

You could possibly limit this to cards that remain powered during
suspend, but doing it always should do no harm.

>  	}
>  
>  out:
> diff --git a/drivers/mmc/core/sdio_irq.c b/drivers/mmc/core/sdio_irq.c
> index d7965b53a6d2..900871073bd7 100644
> --- a/drivers/mmc/core/sdio_irq.c
> +++ b/drivers/mmc/core/sdio_irq.c
> @@ -115,7 +115,8 @@ static void sdio_run_irqs(struct mmc_host *host)
>  	mmc_claim_host(host);
>  	if (host->sdio_irqs) {
>  		process_sdio_pending_irqs(host);
> -		host->ops->ack_sdio_irq(host);
> +		if (!host->sdio_irq_pending)
> +			host->ops->ack_sdio_irq(host);
>  	}
>  	mmc_release_host(host);
>  }

I'm by no means a SDIO expert, but as far as I can tell this looks
good. I verified that this patch fixes a problem with SDIO interrupts
that are ignored while suspending.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>