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    SubjectRe: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
    Date

    Jarkko Sakkinen @ 2020-11-23 20:26 MST:

    > On Wed, Nov 18, 2020 at 11:36:20PM -0700, Jerry Snitselaar wrote:
    >>
    >> Matthew Garrett @ 2020-10-15 15:39 MST:
    >>
    >> > On Thu, Oct 15, 2020 at 2:44 PM Jerry Snitselaar <jsnitsel@redhat.com> wrote:
    >> >>
    >> >> There is a misconfiguration in the bios of the gpio pin used for the
    >> >> interrupt in the T490s. When interrupts are enabled in the tpm_tis
    >> >> driver code this results in an interrupt storm. This was initially
    >> >> reported when we attempted to enable the interrupt code in the tpm_tis
    >> >> driver, which previously wasn't setting a flag to enable it. Due to
    >> >> the reports of the interrupt storm that code was reverted and we went back
    >> >> to polling instead of using interrupts. Now that we know the T490s problem
    >> >> is a firmware issue, add code to check if the system is a T490s and
    >> >> disable interrupts if that is the case. This will allow us to enable
    >> >> interrupts for everyone else. If the user has a fixed bios they can
    >> >> force the enabling of interrupts with tpm_tis.interrupts=1 on the
    >> >> kernel command line.
    >> >
    >> > I think an implication of this is that systems haven't been
    >> > well-tested with interrupts enabled. In general when we've found a
    >> > firmware issue in one place it ends up happening elsewhere as well, so
    >> > it wouldn't surprise me if there are other machines that will also be
    >> > unhappy with interrupts enabled. Would it be possible to automatically
    >> > detect this case (eg, if we get more than a certain number of
    >> > interrupts in a certain timeframe immediately after enabling the
    >> > interrupt) and automatically fall back to polling in that case? It
    >> > would also mean that users with fixed firmware wouldn't need to pass a
    >> > parameter.
    >>
    >> I believe Matthew is correct here. I found another system today
    >> with completely different vendor for both the system and the tpm chip.
    >> In addition another Lenovo model, the L490, has the issue.
    >>
    >> This initial attempt at a solution like Matthew suggested works on
    >> the system I found today, but I imagine it is all sorts of wrong.
    >> In the 2 systems where I've seen it, there are about 100000 interrupts
    >> in around 1.5 seconds, and then the irq code shuts down the interrupt
    >> because they aren't being handled.
    >>
    >>
    >> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
    >> index 49ae09ac604f..478e9d02a3fa 100644
    >> --- a/drivers/char/tpm/tpm_tis_core.c
    >> +++ b/drivers/char/tpm/tpm_tis_core.c
    >> @@ -27,6 +27,11 @@
    >> #include "tpm.h"
    >> #include "tpm_tis_core.h"
    >>
    >> +static unsigned int time_start = 0;
    >> +static bool storm_check = true;
    >> +static bool storm_killed = false;
    >> +static u32 irqs_fired = 0;
    >
    > Maybe kstat_irqs() would be a better idea than ad hoc stats.
    >

    Thanks, yes that would be better.

    >> +
    >> static void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value);
    >>
    >> static void tpm_tis_enable_interrupt(struct tpm_chip *chip, u8 mask)
    >> @@ -464,25 +469,31 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const u8 *buf, size_t len)
    >> return rc;
    >> }
    >>
    >> -static void disable_interrupts(struct tpm_chip *chip)
    >> +static void __disable_interrupts(struct tpm_chip *chip)
    >> {
    >> struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
    >> u32 intmask;
    >> int rc;
    >>
    >> - if (priv->irq == 0)
    >> - return;
    >> -
    >> rc = tpm_tis_read32(priv, TPM_INT_ENABLE(priv->locality), &intmask);
    >> if (rc < 0)
    >> intmask = 0;
    >>
    >> intmask &= ~TPM_GLOBAL_INT_ENABLE;
    >> rc = tpm_tis_write32(priv, TPM_INT_ENABLE(priv->locality), intmask);
    >> + chip->flags &= ~TPM_CHIP_FLAG_IRQ;
    >> +}
    >> +
    >> +static void disable_interrupts(struct tpm_chip *chip)
    >> +{
    >> + struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
    >>
    >> + if (priv->irq == 0)
    >> + return;
    >> +
    >> + __disable_interrupts(chip);
    >> devm_free_irq(chip->dev.parent, priv->irq, chip);
    >> priv->irq = 0;
    >> - chip->flags &= ~TPM_CHIP_FLAG_IRQ;
    >> }
    >>
    >> /*
    >> @@ -528,6 +539,12 @@ static int tpm_tis_send(struct tpm_chip *chip, u8 *buf, size_t len)
    >> int rc, irq;
    >> struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
    >>
    >> + if (unlikely(storm_killed)) {
    >> + devm_free_irq(chip->dev.parent, priv->irq, chip);
    >> + priv->irq = 0;
    >> + storm_killed = false;
    >> + }
    >
    > OK this kind of bad solution because if tpm_tis_send() is not called,
    > then IRQ is never freed. AFAIK, devres_* do not sleep but use spin
    > lock, i.e. you could render out both storm_check and storm_killed.
    >

    Is there a way to flag it for freeing later while in an interrupt
    context? I'm not sure where to clean it up since devm_free_irq can't be
    called in tis_int_handler.

    Before diving further into that though, does anyone else have an opinion
    on ripping out the irq code, and just using polling? We've been only
    polling since 2015 anyways.

    >> +
    >> if (!(chip->flags & TPM_CHIP_FLAG_IRQ) || priv->irq_tested)
    >> return tpm_tis_send_main(chip, buf, len);
    >>
    >> @@ -748,6 +765,21 @@ static irqreturn_t tis_int_handler(int dummy, void *dev_id)
    >> u32 interrupt;
    >> int i, rc;
    >>
    >> + if (storm_check) {
    >> + irqs_fired++;
    >> +
    >> + if (!time_start) {
    >> + time_start = jiffies_to_msecs(jiffies);
    >> + } else if ((irqs_fired > 1000) && (jiffies_to_msecs(jiffies) - jiffies < 500)) {
    >> + __disable_interrupts(chip);
    >> + storm_check = false;
    >> + storm_killed = true;
    >> + return IRQ_HANDLED;
    >> + } else if ((jiffies_to_msecs(jiffies) - time_start > 500) && (irqs_fired < 1000)) {
    >> + storm_check = false;
    >> + }
    >> + }
    >> +
    >> rc = tpm_tis_read32(priv, TPM_INT_STATUS(priv->locality), &interrupt);
    >> if (rc < 0)
    >> return IRQ_NONE;
    >>
    >>
    >
    > /Jarkko

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