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    SubjectRe: [PATCH] tpm_tis: Disable interrupts on ThinkPad T490s
    On Tue, Nov 24, 2020 at 05:27:30AM +0200, Jarkko Sakkinen wrote:
    > On Thu, Nov 19, 2020 at 03:42:35PM +0100, Hans de Goede wrote:
    > > Hi,
    > >
    > > On 11/19/20 7:36 AM, 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.
    > >
    > > Is that with your patch? The IRQ should be silenced as soon as
    > > devm_free_irq(chip->dev.parent, priv->irq, chip); is called.
    > >
    > > Depending on if we can get your storm-detection to work or not,
    > > we might also choose to just never try to use the IRQ (at least on
    > > x86 systems). AFAIK the TPM is never used for high-throughput stuff
    > > so the polling overhead should not be a big deal (and I'm getting the feeling
    > > that Windows always polls).
    > >
    > > Regards,
    > >
    > > Hans
    >
    > Yeah, this is what I've been wondering for a while. Why could not we
    > just strip off IRQ code? Why does it matter?

    And we DO NOT use interrupts in tpm_crb and nobody has ever complained.

    /Jarkko

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