Re: [PATCH v2 2/2] mmc: meson-gx: add SDIO interrupt support

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

On Tue, 23 Aug 2022 at 20:16, Heiner Kallweit <hkallweit1@gmail.com> wrote:
>
> On 22.08.2022 13:33, Ulf Hansson wrote:
> > On Fri, 19 Aug 2022 at 23:14, Heiner Kallweit <hkallweit1@gmail.com> wrote:
> >>
> >> Add SDIO interrupt support. Successfully tested on a S905X4-based
> >> system (V3 register layout) with a BRCM4334 SDIO wifi module
> >> (brcmfmac driver). The implementation also considers the potential
> >> race discussed in [0].
> >>
> >> [0] https://lore.kernel.org/linux-arm-kernel/CAPDyKFoJDhjLkajBHgW3zHasvYYri77NQoDpiW-BpKgkdjtOyg@mail.gmail.com/
> >>
> >> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> >> ---
> >>  drivers/mmc/host/meson-gx-mmc.c | 76 ++++++++++++++++++++++++++++-----
> >>  1 file changed, 66 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
> >> index 9a4da2544..58b7836a5 100644
> >> --- a/drivers/mmc/host/meson-gx-mmc.c
> >> +++ b/drivers/mmc/host/meson-gx-mmc.c
> >> @@ -41,14 +41,17 @@
> >>  #define   CLK_V2_TX_DELAY_MASK GENMASK(19, 16)
> >>  #define   CLK_V2_RX_DELAY_MASK GENMASK(23, 20)
> >>  #define   CLK_V2_ALWAYS_ON BIT(24)
> >> +#define   CLK_V2_IRQ_SDIO_SLEEP BIT(25)
> >>
> >>  #define   CLK_V3_TX_DELAY_MASK GENMASK(21, 16)
> >>  #define   CLK_V3_RX_DELAY_MASK GENMASK(27, 22)
> >>  #define   CLK_V3_ALWAYS_ON BIT(28)
> >> +#define   CLK_V3_IRQ_SDIO_SLEEP BIT(29)
> >>
> >>  #define   CLK_TX_DELAY_MASK(h)         (h->data->tx_delay_mask)
> >>  #define   CLK_RX_DELAY_MASK(h)         (h->data->rx_delay_mask)
> >>  #define   CLK_ALWAYS_ON(h)             (h->data->always_on)
> >> +#define   CLK_IRQ_SDIO_SLEEP(h)                (h->data->irq_sdio_sleep)
> >>
> >>  #define SD_EMMC_DELAY 0x4
> >>  #define SD_EMMC_ADJUST 0x8
> >> @@ -135,6 +138,7 @@ struct meson_mmc_data {
> >>         unsigned int rx_delay_mask;
> >>         unsigned int always_on;
> >>         unsigned int adjust;
> >> +       unsigned int irq_sdio_sleep;
> >>  };
> >>
> >>  struct sd_emmc_desc {
> >> @@ -174,6 +178,7 @@ struct meson_host {
> >>         bool vqmmc_enabled;
> >>         bool needs_pre_post_req;
> >>
> >> +       spinlock_t lock;
> >>  };
> >>
> >>  #define CMD_CFG_LENGTH_MASK GENMASK(8, 0)
> >> @@ -430,6 +435,7 @@ static int meson_mmc_clk_init(struct meson_host *host)
> >>         clk_reg |= FIELD_PREP(CLK_CORE_PHASE_MASK, CLK_PHASE_180);
> >>         clk_reg |= FIELD_PREP(CLK_TX_PHASE_MASK, CLK_PHASE_0);
> >>         clk_reg |= FIELD_PREP(CLK_RX_PHASE_MASK, CLK_PHASE_0);
> >> +       clk_reg |= CLK_IRQ_SDIO_SLEEP(host);
> >>         writel(clk_reg, host->regs + SD_EMMC_CLOCK);
> >>
> >>         /* get the mux parents */
> >> @@ -934,32 +940,54 @@ static void meson_mmc_read_resp(struct mmc_host *mmc, struct mmc_command *cmd)
> >>         }
> >>  }
> >>
> >> +static void __meson_mmc_enable_sdio_irq(struct mmc_host *mmc, int enable)
> >> +{
> >> +       struct meson_host *host = mmc_priv(mmc);
> >> +       u32 reg_irqen = IRQ_EN_MASK;
> >> +
> >> +       if (enable)
> >> +               reg_irqen |= IRQ_SDIO;
> >> +       writel(reg_irqen, host->regs + SD_EMMC_IRQ_EN);
> >> +}
> >> +
> >>  static irqreturn_t meson_mmc_irq(int irq, void *dev_id)
> >>  {
> >>         struct meson_host *host = dev_id;
> >>         struct mmc_command *cmd;
> >> -       struct mmc_data *data;
> >>         u32 status, raw_status;
> >>         irqreturn_t ret = IRQ_NONE;
> >>
> >>         raw_status = readl(host->regs + SD_EMMC_STATUS);
> >> -       status = raw_status & IRQ_EN_MASK;
> >> +       status = raw_status & (IRQ_EN_MASK | IRQ_SDIO);
> >>
> >>         if (!status) {
> >>                 dev_dbg(host->dev,
> >>                         "Unexpected IRQ! irq_en 0x%08lx - status 0x%08x\n",
> >> -                        IRQ_EN_MASK, raw_status);
> >> +                        IRQ_EN_MASK | IRQ_SDIO, raw_status);
> >>                 return IRQ_NONE;
> >>         }
> >>
> >> -       if (WARN_ON(!host) || WARN_ON(!host->cmd))
> >> +       if (WARN_ON(!host))
> >>                 return IRQ_NONE;
> >>
> >>         /* ack all raised interrupts */
> >>         writel(status, host->regs + SD_EMMC_STATUS);
> >>
> >>         cmd = host->cmd;
> >> -       data = cmd->data;
> >> +
> >> +       if (status & IRQ_SDIO) {
> >> +               spin_lock(&host->lock);
> >> +               __meson_mmc_enable_sdio_irq(host->mmc, 0);
> >> +               sdio_signal_irq(host->mmc);
> >> +               spin_unlock(&host->lock);
> >> +               status &= ~IRQ_SDIO;
> >> +               if (!status)
> >> +                       return IRQ_HANDLED;
> >> +       }
> >> +
> >> +       if (WARN_ON(!cmd))
> >> +               return IRQ_NONE;
> >> +
> >>         cmd->error = 0;
> >>         if (status & IRQ_CRC_ERR) {
> >>                 dev_dbg(host->dev, "CRC Error - status 0x%08x\n", status);
> >> @@ -977,12 +1005,9 @@ static irqreturn_t meson_mmc_irq(int irq, void *dev_id)
> >>
> >>         meson_mmc_read_resp(host->mmc, cmd);
> >>
> >> -       if (status & IRQ_SDIO) {
> >> -               dev_dbg(host->dev, "IRQ: SDIO TODO.\n");
> >> -               ret = IRQ_HANDLED;
> >> -       }
> >> -
> >>         if (status & (IRQ_END_OF_CHAIN | IRQ_RESP_STATUS)) {
> >> +               struct mmc_data *data = cmd->data;
> >> +
> >>                 if (data && !cmd->error)
> >>                         data->bytes_xfered = data->blksz * data->blocks;
> >>                 if (meson_mmc_bounce_buf_read(data) ||
> >> @@ -1125,6 +1150,27 @@ static int meson_mmc_voltage_switch(struct mmc_host *mmc, struct mmc_ios *ios)
> >>         return -EINVAL;
> >>  }
> >>
> >> +static void meson_mmc_enable_sdio_irq(struct mmc_host *mmc, int enable)
> >> +{
> >> +       struct meson_host *host = mmc_priv(mmc);
> >> +       unsigned long flags;
> >> +
> >> +       spin_lock_irqsave(&host->lock, flags);
> >> +       __meson_mmc_enable_sdio_irq(mmc, enable);
> >> +       spin_unlock_irqrestore(&host->lock, flags);
> >> +}
> >> +
> >> +static void meson_mmc_ack_sdio_irq(struct mmc_host *mmc)
> >> +{
> >> +       struct meson_host *host = mmc_priv(mmc);
> >> +       unsigned long flags;
> >> +
> >> +       spin_lock_irqsave(&host->lock, flags);
> >> +       if (!mmc->sdio_irq_pending)
> >
> > I am not quite sure I understand why you need to check this flag here.
> >
> > The point is, in meson_mmc_irq() you are doing things in the correct
> > order, which means disabling the SDIO irq by calling
> > __meson_mmc_enable_sdio_irq(host->mmc, 0) prior calling
> > sdio_signal_irq(host->mmc) (which sets the flag).
> >
> > In this way, the host driver should be prevented from signaling
> > another new SDIO irq, until it has acked (which means re-enabling the
> > SDIO irqs) the current one to be processed.
> >
> > Or did I miss something?
> >
>
> What could happen (at least based on the code):
> Even though SDIO IRQ signalling is disabled we may receive another
> interrupt that by chance has also the SDIO IRQ status bit set.

That sounds like a broken HW to me, but I get your point.

> And if the hard irq handler interrupts sdio_run_irqs() here then
> we may have a problem.
>
> if (!host->sdio_irq_pending)
>         host->ops->ack_sdio_irq(host);
>
> Therefore the additional check (because checking the flag and calling
> __meson_mmc_enable_sdio_irq() is protected by the spinlock).
> However that's a theoretical worst case scenario. It don't know enough
> about SDIO interrupts to state whether it actually can happen.

If you are worried about getting spurious IRQs with the SDIO IRQ
status bit set, then I prefer that you use a meson host driver
specific flag. The flag could indicate whether the IRQ_SDIO bit has
been set in the IRQ_EN_MASK (__meson_mmc_enable_sdio_irq()) and then
simply prevent (or postpone) signaling a new SDIO IRQ
(sdio_signal_irq()).

>
> By the way: I'd also be reluctant to omit checking the SDIO IRQ status bit
> if host->sdio_irq_pending is true because then we might miss a SDIO interrupt.

Again, that sounds like a broken HW to me.

If you are worried that we may miss an SDIO irq, then it's seems
better to "cache" that additional SDIO IRQ in a state variable (from
the irq handler) and then check that variable in ->ack_sdio_irq() to
immediately signal a new SDIO irq (sdio_signal_irq()).

>
> But if you say it's not needed I'll remove the duplicated flag check.

Let me put it like this, if the HW works as expected, the additional
check/protection should not be needed. So in the end, this is your
call.

>
> >> +               __meson_mmc_enable_sdio_irq(mmc, 1);
> >> +       spin_unlock_irqrestore(&host->lock, flags);
> >> +}
> >>

[...]

Kind regards
Uffe

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