Re: [PATCH 1/1] mmc: mmci: add threaded irq to abort DPSM of non-functional state

[Ulf Hansson <ulf.hansson@linaro.org>]

On Wed, 13 Nov 2019 at 18:25, Ludovic Barre <ludovic.Barre@st.com> wrote:
>
> From: Ludovic Barre <ludovic.barre@st.com>
>
> If datatimeout occurs on R1B request, the Data Path State Machine stays
> in busy and is non-functional. Only a reset aborts the DPSM.

Please clarify/extend this information to tell that this is for the
variant, that keeps DPSM enabled and uses the data timer while sending
a CMD12. Or something along those lines.

>
> Like a reset must be outside of critical section, this patch adds

/s/critical section/atomic context

> threaded irq function to release state machine. In this case,
> the mmc_request_done is called at the end of threaded irq and
> skipped into irq handler.
>
> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
> ---
>  drivers/mmc/host/mmci.c | 44 ++++++++++++++++++++++++++++++++++++-----
>  drivers/mmc/host/mmci.h |  1 +
>  2 files changed, 40 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> index 40e72c30ea84..ec6e249c87ca 100644
> --- a/drivers/mmc/host/mmci.c
> +++ b/drivers/mmc/host/mmci.c
> @@ -556,6 +556,9 @@ static void mmci_dma_error(struct mmci_host *host)
>  static void
>  mmci_request_end(struct mmci_host *host, struct mmc_request *mrq)
>  {
> +       if (host->irq_action == IRQ_WAKE_THREAD)
> +               return;
> +
>         writel(0, host->base + MMCICOMMAND);
>
>         BUG_ON(host->data);
> @@ -1321,6 +1324,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
>         } else if (host->variant->busy_timeout && busy_resp &&
>                    status & MCI_DATATIMEOUT) {
>                 cmd->error = -ETIMEDOUT;
> +               host->irq_action = IRQ_WAKE_THREAD;
>         } else {
>                 cmd->resp[0] = readl(base + MMCIRESPONSE0);
>                 cmd->resp[1] = readl(base + MMCIRESPONSE1);
> @@ -1532,9 +1536,9 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
>  {
>         struct mmci_host *host = dev_id;
>         u32 status;
> -       int ret = 0;
>
>         spin_lock(&host->lock);
> +       host->irq_action = IRQ_HANDLED;
>
>         do {
>                 status = readl(host->base + MMCISTATUS);
> @@ -1574,12 +1578,41 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
>                 if (host->variant->busy_detect_flag)
>                         status &= ~host->variant->busy_detect_flag;
>
> -               ret = 1;
>         } while (status);
>
>         spin_unlock(&host->lock);
>
> -       return IRQ_RETVAL(ret);
> +       return host->irq_action;
> +}
> +
> +/*
> + * mmci_irq_threaded is call if the mmci host need to release state machines
> + * before to terminate the request.
> + * If datatimeout occurs on R1B request, the Data Path State Machine stays
> + * in busy and is non-functional. Only a reset can to abort the DPSM.
> + */
> +static irqreturn_t mmci_irq_threaded(int irq, void *dev_id)
> +{
> +       struct mmci_host *host = dev_id;
> +       unsigned long flags;
> +
> +       if (host->rst) {
> +               reset_control_assert(host->rst);
> +               udelay(2);
> +               reset_control_deassert(host->rst);
> +       }
> +
> +       spin_lock_irqsave(&host->lock, flags);
> +       writel(host->clk_reg, host->base + MMCICLOCK);
> +       writel(host->pwr_reg, host->base + MMCIPOWER);
> +       writel(MCI_IRQENABLE | host->variant->start_err,
> +              host->base + MMCIMASK0);
> +
> +       host->irq_action = IRQ_HANDLED;
> +       mmci_request_end(host, host->mrq);
> +       spin_unlock_irqrestore(&host->lock, flags);
> +
> +       return host->irq_action;
>  }
>
>  static void mmci_request(struct mmc_host *mmc, struct mmc_request *mrq)
> @@ -2071,8 +2104,9 @@ static int mmci_probe(struct amba_device *dev,
>                         goto clk_disable;
>         }
>
> -       ret = devm_request_irq(&dev->dev, dev->irq[0], mmci_irq, IRQF_SHARED,
> -                       DRIVER_NAME " (cmd)", host);
> +       ret = devm_request_threaded_irq(&dev->dev, dev->irq[0], mmci_irq,
> +                                       mmci_irq_threaded, IRQF_SHARED,
> +                                       DRIVER_NAME " (cmd)", host);

In general it's a good idea to move drivers into using a threaded IRQ handler.

However, the reason this hasn't been done for mmci before, is because
there are some legacy variants, that doesn't support HW flow control.

Unless I am mistaken, that means when the fifo gets full during data
transfers - it's too late to act. In other words, running the handler
in hard IRQ context, should increase the probability of not missing
the deadline.

If a threaded IRQ handler also is sufficient for these legacy
variants, only tests can tell.

An option, would be to use a threaded handler for those variants that
supports HW flow control. Not sure how messy the code would be with
this option, perhaps you can give this a try?


>         if (ret)
>                 goto clk_disable;
>
> diff --git a/drivers/mmc/host/mmci.h b/drivers/mmc/host/mmci.h
> index 158e1231aa23..5e63c0596364 100644
> --- a/drivers/mmc/host/mmci.h
> +++ b/drivers/mmc/host/mmci.h
> @@ -412,6 +412,7 @@ struct mmci_host {
>
>         struct timer_list       timer;
>         unsigned int            oldstat;
> +       u32                     irq_action;
>
>         /* pio stuff */
>         struct sg_mapping_iter  sg_miter;
> --
> 2.17.1
>

Kind regards
Uffe