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

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

On Fri, 4 Oct 2019 at 14:59, Ludovic BARRE <ludovic.barre@st.com> wrote:
>
> hi Ulf
>
> Le 10/4/19 à 8:20 AM, Ulf Hansson a écrit :
> > On Fri, 4 Oct 2019 at 08:12, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> >>
> >> On Thu, 5 Sep 2019 at 14:21, Ludovic Barre <ludovic.Barre@st.com> wrote:
> >>>
> >>> From: Ludovic Barre <ludovic.barre@st.com>
> >>>
> >>> 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).
>
> Thanks for the re-phrasing.
>
> >> -----
> >>
> >> 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.
>
> OK, I will set 10s, the max_busy_timeout could be very long for small
> frequencies (example, 25Mhz => 171s).
>
> >>
> >>> -Add MCI_DATATIMEOUT error management in mmci_cmd_irq.
> >>>
> >>> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
> >>> ---
> >>>   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..
>
> you're referring to "return" of ?
>         if (host->busy_status &&
>             (status & host->variant->busy_detect_flag)) {
>                 writel(host->variant->busy_detect_mask,
>                        host->base + MMCICLEAR);
>                 return;
>         }
>
> For stm32 variant (in patch 3/3): the "busy completion" is
> released immediately if there is an error or busyd0end,
> and cleans: irq, busyd0end mask, busy_status variable.

Right, thanks for clarifying!

>
> I could add similar action in patch 2/3 function: "ux500_busy_complete"
>
> static bool ux500_busy_complete(struct mmci_host *host, u32 status, u32
> err_msk)
> {
>         void __iomem *base = host->base;
>
>         if (status & err_msk)
>                 goto complete;
> ...
> complete:
>         /* specific action to clean busy detection, irq, mask, busy_status */
> }
>
> what do you think about it?

For the legacy variant, the MCI_DATATIMEOUT isn't an issue as it can't
be raised while waiting for busyend. So, I think this is fine as is.

Kind regards
Uffe