Re: [PATCH 1/4] mmc: mmci: avoid fake busy polling

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

On Thu, 25 Apr 2019 at 11:22, Ludovic BARRE <ludovic.barre@st.com> wrote:
>
> hi Ulf
>
> On 4/23/19 3:39 PM, Ulf Hansson wrote:
> > On Tue, 5 Mar 2019 at 17:10, Ludovic Barre <ludovic.Barre@st.com> wrote:
> >>
> >> From: Ludovic Barre <ludovic.barre@st.com>
> >>
> >> The busy status bit could occurred even if no busy response is
> >> expected (example cmd11). On sdmmc variant, the busy_detect_flag
> >> reflects inverted value of d0 state, it's sampled at the end of a
> >> CMD response and a second time 2 clk cycles after the CMD response.
> >> To avoid a fake busy, the busy status could be checked and polled
> >> only if the command has RSP_BUSY flag.
> >
> > I would appreciate a better explanation of what this patch really changes.
> >
> > The above is giving some background to the behavior of sdmmc variant,
> > but at this point that variant doesn't even have the
> > ->variant->busy_detect flag set.
> >
>
> Yes, I will try to explain more and focus on common behavior.
>
> >>
> >> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
> >> ---
> >>   drivers/mmc/host/mmci.c | 19 +++++++++++++------
> >>   1 file changed, 13 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> >> index 387ff14..4901b73 100644
> >> --- a/drivers/mmc/host/mmci.c
> >> +++ b/drivers/mmc/host/mmci.c
> >> @@ -1220,12 +1220,13 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >>               unsigned int status)
> >>   {
> >>          void __iomem *base = host->base;
> >> -       bool sbc;
> >> +       bool sbc, busy_resp;
> >>
> >>          if (!cmd)
> >>                  return;
> >>
> >>          sbc = (cmd == host->mrq->sbc);
> >> +       busy_resp = !!(cmd->flags & MMC_RSP_BUSY);
> >>
> >>          /*
> >>           * We need to be one of these interrupts to be considered worth
> >> @@ -1239,8 +1240,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >>          /*
> >>           * ST Micro variant: handle busy detection.
> >>           */
> >> -       if (host->variant->busy_detect) {
> >> -               bool busy_resp = !!(cmd->flags & MMC_RSP_BUSY);
> >> +       if (busy_resp && host->variant->busy_detect) {
> >>
> >>                  /* We are busy with a command, return */
> >>                  if (host->busy_status &&
> >> @@ -1253,7 +1253,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
> >>                   * that the special busy status bit is still set before
> >>                   * proceeding.
> >>                   */
> >> -               if (!host->busy_status && busy_resp &&
> >> +               if (!host->busy_status &&
> >>                      !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) &&
> >>                      (readl(base + MMCISTATUS) & host->variant->busy_detect_flag)) {
> >
> > All the changes above makes perfect sense to me, but looks more like a
> > cleanup of the code, rather than actually changing the behavior.
>
> yes, few changing (this just avoid to enter in
> "if (host->variant->busy_detect)") at each time.
> I could move this part in cleanup patch (before this patch)

Sounds good to me!

>
> >
> >>
> >> @@ -1508,6 +1508,7 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
> >>   {
> >>          struct mmci_host *host = dev_id;
> >>          u32 status;
> >> +       bool busy_resp;
> >>          int ret = 0;
> >>
> >>          spin_lock(&host->lock);
> >> @@ -1550,9 +1551,15 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
> >>                  }
> >>
> >>                  /*
> >> -                * Don't poll for busy completion in irq context.
> >> +                * Don't poll for:
> >> +                * -busy completion in irq context.
> >> +                * -no busy response expected.
> >>                   */
> >> -               if (host->variant->busy_detect && host->busy_status)
> >> +               busy_resp = host->cmd ?
> >> +                       !!(host->cmd->flags & MMC_RSP_BUSY) : false;
> >
> > This doesn't make sense to me, but I may be missing something.
> >
> > host->busy_status is being updated by mmci_cmd_irq() and only when
> > MMC_RSP_BUSY is set for the command in flight. In other words,
> > checking for MMC_RSP_BUSY here as well is redundant. No?
>
> In mmci_irq the "do while" loops until the status is totally cleared.
>
> Today (for variant with busy_detect option), the status busy_detect_flag
> is excluded only while busy_status period (command with MMC_RSP_BUSY and
> while busy line is low => "busy_status=1")
>
> On SDMMC variant I noticed that busy_detect_flag status could be enabled
> even if the command is not MMC_RSP_BUSY, for example sdmmc variant stay
> in loop while cmd11 voltage switch.

Right, I see.

>
> So I wish extend host->variant->busy_detect_flag exclusion for all
> commands which is not a MMC_RSP_BUSY. I suppose that other variants
> could have the same behavior, and else there is no impact, normally.

I am guessing this is because the variant->busy_dpsm_flag has been set
in the datactrl register, which is needed for mmci_card_busy().

That said, I am kind of wondering if we ever should need repeat the
while loop if 'status' contains the bit for
host->variant->busy_detect_flag. I mean we have already called
mmci_cmd_irq() to handle it.

So, couldn't we just always do:

if (host->variant->busy_detect_flag)
    status &= ~host->variant->busy_detect_flag;

No?

>
> >
> >> +
> >> +               if (host->variant->busy_detect &&
> >> +                   (!busy_resp || host->busy_status))
> >>                          status &= ~host->variant->busy_detect_flag;
> >>
> >>                  ret = 1;
> >> --
> >> 2.7.4
> >>
> >
> > Kind regards
> > Uffe
> >

Kind regards
Uffe