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

    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;
    +
    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;
    + }
    +
    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;
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