Re: [PATCH V6 1/3] mmc: mmci: add hardware busy timeout feature

[Ulf Hansson]

On Fri, 4 Oct 2019 at 08:12, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Thu, 5 Sep 2019 at 14:21, Ludovic Barre <ludovic.Barre@xxxxxx> wrote:
> >
> > From: Ludovic Barre <ludovic.barre@xxxxxx>
> >
> > In some variants, the data timer starts and decrements
> > when the DPSM enters in Wait_R or Busy state
> > (while data transfer or MMC_RSP_BUSY), and generates a
> > data timeout error if the counter reach 0.
>
>
> >
> > -Define max_busy_timeout (in ms) according to clock.
> > -Set data timer register if the command has rsp_busy flag.
> >  If busy_timeout is not defined by framework, the busy
> >  length after Data Burst is defined as 1 second
> >  (refer: 4.6.2.2 Write of sd specification part1 v6-0).
>
> How about re-phrasing this as below:
>
> -----
> In the stm32_sdmmc variant, the datatimer is active not only during
> data transfers with the DPSM, but also while waiting for the busyend
> IRQs from commands having the MMC_RSP_BUSY flag set. This leads to an
> incorrect IRQ being raised to signal MCI_DATATIMEOUT error, which
> simply breaks the behaviour.
>
> Address this by updating the datatimer value before sending a command
> having the MMC_RSP_BUSY flag set. To inform the mmc core about the
> maximum supported busy timeout, which also depends on the current
> clock rate, set ->max_busy_timeout (in ms).
> -----
>
> Regarding the busy_timeout, the core should really assign it a value
> for all commands having the RSP_BUSY flag set. However, I realize the
> core needs to be improved to cover all these cases - and I am looking
> at that, but not there yet.
>
> I would also suggest to use a greater value than 1s, as that seems a
> bit low for the "undefined" case. Perhaps use the max_busy_timeout,
> which would be nice a simple or 10s, which I think is used by some
> other drivers.
>
> > -Add MCI_DATATIMEOUT error management in mmci_cmd_irq.
> >
> > Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx>
> > ---
> >  drivers/mmc/host/mmci.c | 42 ++++++++++++++++++++++++++++++++++++-----
> >  drivers/mmc/host/mmci.h |  3 +++
> >  2 files changed, 40 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> > index c37e70dbe250..c30319255dc2 100644
> > --- a/drivers/mmc/host/mmci.c
> > +++ b/drivers/mmc/host/mmci.c
> > @@ -1075,6 +1075,7 @@ static void
> >  mmci_start_command(struct mmci_host *host, struct mmc_command *cmd, u32 c)
> >  {
> >         void __iomem *base = host->base;
> > +       unsigned long long clks;
> >
> >         dev_dbg(mmc_dev(host->mmc), "op %02x arg %08x flags %08x\n",
> >             cmd->opcode, cmd->arg, cmd->flags);
> > @@ -1097,6 +1098,16 @@ mmci_start_command(struct mmci_host *host, struct mmc_command *cmd, u32 c)
> >                 else
> >                         c |= host->variant->cmdreg_srsp;
> >         }
> > +
> > +       if (host->variant->busy_timeout && cmd->flags & MMC_RSP_BUSY) {
> > +               if (!cmd->busy_timeout)
> > +                       cmd->busy_timeout = 1000;
> > +
> > +               clks = (unsigned long long)cmd->busy_timeout * host->cclk;
> > +               do_div(clks, MSEC_PER_SEC);
> > +               writel_relaxed(clks, host->base + MMCIDATATIMER);
> > +       }
> > +
> >         if (/*interrupt*/0)
> >                 c |= MCI_CPSM_INTERRUPT;
> >
> > @@ -1201,6 +1212,7 @@ static void
> >  mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >              unsigned int status)
> >  {
> > +       u32 err_msk = MCI_CMDCRCFAIL | MCI_CMDTIMEOUT;
> >         void __iomem *base = host->base;
> >         bool sbc, busy_resp;
> >
> > @@ -1215,8 +1227,11 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >          * handling. Note that we tag on any latent IRQs postponed
> >          * due to waiting for busy status.
> >          */
> > -       if (!((status|host->busy_status) &
> > -             (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT|MCI_CMDSENT|MCI_CMDRESPEND)))
> > +       if (host->variant->busy_timeout && busy_resp)
> > +               err_msk |= MCI_DATATIMEOUT;
> > +
> > +       if (!((status | host->busy_status) &
> > +             (err_msk | MCI_CMDSENT | MCI_CMDRESPEND)))
> >                 return;
> >
> >         /* Handle busy detection on DAT0 if the variant supports it. */
> > @@ -1235,8 +1250,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >                  * while, to allow it to be set, but tests indicates that it
> >                  * isn't needed.
> >                  */
> > -               if (!host->busy_status &&
> > -                   !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) &&
> > +               if (!host->busy_status && !(status & err_msk) &&
> >                     (readl(base + MMCISTATUS) & host->variant->busy_detect_flag)) {
> >
> >                         writel(readl(base + MMCIMASK0) |
> > @@ -1290,6 +1304,9 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >                 cmd->error = -ETIMEDOUT;
> >         } else if (status & MCI_CMDCRCFAIL && cmd->flags & MMC_RSP_CRC) {
> >                 cmd->error = -EILSEQ;
> > +       } else if (host->variant->busy_timeout && busy_resp &&
> > +                  status & MCI_DATATIMEOUT) {
> > +               cmd->error = -ETIMEDOUT;
>
> It's not really clear to me what happens with the busy detection
> status bit (variant->busy_detect_flag), in case a MCI_DATATIMEOUT IRQ
> is raised, while also having host->busy_status set (waiting for
> busyend).
>
> By looking at the code a few lines above this, we may do a "return;"
> while waiting for the busyend IRQ even if MCI_DATATIMEOUT also is
> raised, potentially losing that from being caught. Is that really
> correct?

A second thought. That "return;" is to manage the busyend IRQ being
raised of the first edge due to broken HW. So I guess, this isn't an
issue for stm32_sdmmc variant after all?

I have a look at the next patches in the series..

[...]

Kind regards
Uffe