Re: [PATCH 2/3] mmc: dw_mmc: Convert to use MMC_CAP2_SDIO_IRQ_NOTHREAD for SDIO IRQs

[Doug Anderson <dianders@google.com>]

Hi,

On Tue, Apr 18, 2017 at 5:32 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> Convert to use the more lightweight method for processing SDIO IRQs, which
> involves the following changes:
>
> - Enable MMC_CAP2_SDIO_IRQ_NOTHREAD when SDIO IRQ is supported.
> - Mask SDIO IRQ when signaling it for processing.
> - Re-enable (unmask) the SDIO IRQ from the ->ack_sdio_irq() callback.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>  drivers/mmc/host/dw_mmc.c | 29 ++++++++++++++++++++++++++---
>  1 file changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 249ded6..f086791 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1635,9 +1635,8 @@ static void dw_mci_init_card(struct mmc_host *mmc, struct mmc_card *card)
>         }
>  }
>
> -static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
> +static void __dw_mci_enable_sdio_irq(struct dw_mci_slot *slot, int enb)
>  {
> -       struct dw_mci_slot *slot = mmc_priv(mmc);
>         struct dw_mci *host = slot->host;
>         unsigned long irqflags;
>         u32 int_mask;
> @@ -1655,6 +1654,20 @@ static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
>         spin_unlock_irqrestore(&host->irq_lock, irqflags);
>  }
>
> +static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
> +{
> +       struct dw_mci_slot *slot = mmc_priv(mmc);
> +
> +       __dw_mci_enable_sdio_irq(slot, enb);
> +}
> +
> +static void dw_mci_ack_sdio_irq(struct mmc_host *mmc)
> +{
> +       struct dw_mci_slot *slot = mmc_priv(mmc);
> +
> +       __dw_mci_enable_sdio_irq(slot, 1);

I have some slight paranoia that some code out there might decide to
call enable_sdio_irq(0) while an interrupt is being processed.  In
that case we'll be turning interrupts back on here.  It seems like it
would be "better safe than sorry" to keep track of the "enabled /
disabled" state somewhere.  ...and when we "unmask" we treat it as a
no-op if the interrupt is currently disabled.

> +}
> +
>  static int dw_mci_execute_tuning(struct mmc_host *mmc, u32 opcode)
>  {
>         struct dw_mci_slot *slot = mmc_priv(mmc);
> @@ -1756,6 +1769,7 @@ static const struct mmc_host_ops dw_mci_ops = {
>         .get_cd                 = dw_mci_get_cd,
>         .hw_reset               = dw_mci_hw_reset,
>         .enable_sdio_irq        = dw_mci_enable_sdio_irq,
> +       .ack_sdio_irq           = dw_mci_ack_sdio_irq,
>         .execute_tuning         = dw_mci_execute_tuning,
>         .card_busy              = dw_mci_card_busy,
>         .start_signal_voltage_switch = dw_mci_switch_voltage,
> @@ -2645,9 +2659,14 @@ static irqreturn_t dw_mci_interrupt(int irq, void *dev_id)
>                                 continue;
>
>                         if (pending & SDMMC_INT_SDIO(slot->sdio_id)) {
> +                               u32 int_mask;
> +
>                                 mci_writel(host, RINTSTS,
>                                            SDMMC_INT_SDIO(slot->sdio_id));
> -                               mmc_signal_sdio_irq(slot->mmc);
> +                               int_mask = mci_readl(host, INTMASK);
> +                               int_mask &= ~SDMMC_INT_SDIO(slot->sdio_id);
> +                               mci_writel(host, INTMASK, int_mask);

Seems like you should be calling "__dw_mci_enable_sdio_irq(slot, 0)"
here.  Specifically the interrupt handler won't have the spinlock so
you're doing an unsafe read/modify/write here.  Yeah, the spinlock is
kinda silly in dw_mmc.  Really the whole interrupt handling needs to
be re-done to use a threaded IRQ instead of the current solution...

> +                               sdio_signal_irq(slot->mmc);
>                         }
>                 }
>
> @@ -2748,6 +2767,10 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
>         if (ret)
>                 goto err_host_allocated;
>
> +       /* Process SDIO IRQs through the sdio_irq_work. */
> +       if (mmc->caps & MMC_CAP_SDIO_IRQ)
> +               mmc->caps2 |= MMC_CAP2_SDIO_IRQ_NOTHREAD;
> +
>         /* Useful defaults if platform data is unset. */
>         if (host->use_dma == TRANS_MODE_IDMAC) {
>                 mmc->max_segs = host->ring_size;
> --
> 2.7.4
>