linux-kernel - Re: [PATCH 1/2] mmc: cqhci: Add a quirk to clear stale TC

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Message-ID: <ZUOtAePhW5O_40wV@google.com>
Date:   Thu, 2 Nov 2023 14:06:57 +0000
From:   Kornel Dulęba <korneld@...omium.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Radoslaw Biernacki <biernacki@...gle.com>,
        Gwendal Grignou <gwendal@...omium.org>
Subject: Re: [PATCH 1/2] mmc: cqhci: Add a quirk to clear stale TC

On Thu, Nov 02, 2023 at 01:01:22PM +0200, Adrian Hunter wrote:
> On 2/11/23 11:21, Kornel Dulęba wrote:
> > On Mon, Oct 30, 2023 at 8:31 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
> >>
> >> On 27/10/23 17:56, Kornel Dulęba wrote:
> >>> This fix addresses a stale task completion event issued right after the
> >>> CQE recovery. As it's a hardware issue the fix is done in form of a
> >>> quirk.
> >>>
> >>> When error interrupt is received the driver runs recovery logic is run.
> >>> It halts the controller, clears all pending tasks, and then re-enables
> >>> it. On some platforms a stale task completion event is observed,
> >>> regardless of the CQHCI_CLEAR_ALL_TASKS bit being set.
> >>>
> >>> This results in either:
> >>> a) Spurious TC completion event for an empty slot.
> >>> b) Corrupted data being passed up the stack, as a result of premature
> >>>    completion for a newly added task.
> >>>
> >>> To fix that re-enable the controller, clear task completion bits,
> >>> interrupt status register and halt it again.
> >>> This is done at the end of the recovery process, right before interrupts
> >>> are re-enabled.
> >>>
> >>> Signed-off-by: Kornel Dulęba <korneld@...omium.org>
> >>> ---
> >>>  drivers/mmc/host/cqhci-core.c | 42 +++++++++++++++++++++++++++++++++++
> >>>  drivers/mmc/host/cqhci.h      |  1 +
> >>>  2 files changed, 43 insertions(+)
> >>>
> >>> diff --git a/drivers/mmc/host/cqhci-core.c b/drivers/mmc/host/cqhci-core.c
> >>> index b3d7d6d8d654..e534222df90c 100644
> >>> --- a/drivers/mmc/host/cqhci-core.c
> >>> +++ b/drivers/mmc/host/cqhci-core.c
> >>> @@ -1062,6 +1062,45 @@ static void cqhci_recover_mrqs(struct cqhci_host *cq_host)
> >>>  /* CQHCI could be expected to clear it's internal state pretty quickly */
> >>>  #define CQHCI_CLEAR_TIMEOUT          20
> >>>
> >>> +/*
> >>> + * During CQE recovery all pending tasks are cleared from the
> >>> + * controller and its state is being reset.
> >>> + * On some platforms the controller sets a task completion bit for
> >>> + * a stale(previously cleared) task right after being re-enabled.
> >>> + * This results in a spurious interrupt at best and corrupted data
> >>> + * being passed up the stack at worst. The latter happens when
> >>> + * the driver enqueues a new request on the problematic task slot
> >>> + * before the "spurious" task completion interrupt is handled.
> >>> + * To fix it:
> >>> + * 1. Re-enable controller by clearing the halt flag.
> >>> + * 2. Clear interrupt status and the task completion register.
> >>> + * 3. Halt the controller again to be consistent with quirkless logic.
> >>> + *
> >>> + * This assumes that there are no pending requests on the queue.
> >>> + */
> >>> +static void cqhci_quirk_clear_stale_tc(struct cqhci_host *cq_host)
> >>> +{
> >>> +     u32 reg;
> >>> +
> >>> +     WARN_ON(cq_host->qcnt);
> >>> +     cqhci_writel(cq_host, 0, CQHCI_CTL);
> >>> +     if ((cqhci_readl(cq_host, CQHCI_CTL) & CQHCI_HALT)) {
> >>> +             pr_err("%s: cqhci: CQE failed to exit halt state\n",
> >>> +                     mmc_hostname(cq_host->mmc));
> >>> +     }
> >>> +     reg = cqhci_readl(cq_host, CQHCI_TCN);
> >>> +     cqhci_writel(cq_host, reg, CQHCI_TCN);
> >>> +     reg = cqhci_readl(cq_host, CQHCI_IS);
> >>> +     cqhci_writel(cq_host, reg, CQHCI_IS);
> >>> +
> >>> +     /*
> >>> +      * Halt the controller again.
> >>> +      * This is only needed so that we're consistent across quirk
> >>> +      * and quirkless logic.
> >>> +      */
> >>> +     cqhci_halt(cq_host->mmc, CQHCI_FINISH_HALT_TIMEOUT);
> >>> +}
> >>
> >> Thanks a lot for tracking this down!
> >>
> >> It could be that the "un-halt" starts a task, so it would be
> >> better to force the "clear" to work if possible, which
> >> should be the case if CQE is disabled.
> >>
> >> Would you mind trying the code below?  Note the increased
> >> CQHCI_START_HALT_TIMEOUT helps avoid trying to clear tasks
> >> when CQE has not halted.
> > 
> > I've run a quick test and it works just fine.
> 
> Thank you!
> 
> > Your approach looks better than what I proposed, since as you
> > mentioned, doing it like this avoids some weird side effects, e.g. DMA
> > to freed memory.
> > Do you plan to include it in the other series that you posted yesterday?
> 
> Yes I will do that

Feel free to add "Tested-by: Kornel Dulęba <korneld@...omium.org>" and
maybe "Reported-by".