Re: [PATCH] tpm_tis_core: Disable broken IRQ handling code

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Thu, May 07, 2020 at 02:51:43PM -0700, Dan Williams wrote:
> On Thu, May 7, 2020 at 7:17 AM Jerry Snitselaar <jsnitsel@redhat.com> wrote:
> >
> > On Thu May 07 20, Hans de Goede wrote:
> > >Hi All,
> > >
> > >On 4/10/20 11:06 PM, Jarkko Sakkinen wrote:
> > >>On Thu, Apr 09, 2020 at 11:10:44PM +0200, Hans de Goede wrote:
> > >>>Since commit dda8b2af395b ("tpm: Revert "tpm_tis_core: Set
> > >>>TPM_CHIP_FLAG_IRQ before probing for interrupts"") we no longer set
> > >>>the TPM_CHIP_FLAG_IRQ ever.
> > >>>
> > >>>So the whole IRQ probing code is not useful, worse we rely on the
> > >>>IRQ-test path of tpm_tis_send() to call disable_interrupts() if
> > >>>interrupts do not work, but that path never gets entered because we
> > >>>never set the TPM_CHIP_FLAG_IRQ.
> > >>>
> > >>>So the remaining IRQ probe code calls request_irq() and never calls
> > >>>free_irq() even when the interrupt is not working.
> > >>>
> > >>>On some systems, e.g. the Lenovo X1 8th gen,  the interrupt we try
> > >>>to use and never free creates an interrupt storm followed by
> > >>>an "irq XX: nobody cared" oops.
> > >>>
> > >>>Since it is non-functional at the moment anyways, lets just completely
> > >>>disable the IRQ code in tpm_tis_core for now.
> > >>>
> > >>>Fixes: dda8b2af395b ("tpm: Revert "tpm_tis_core: Set TPM_CHIP_FLAG_IRQ before probing for interrupts"")
> > >>>Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> > >>>---
> > >>>Note I'm working with Lenovo to try and get to the bottom of this.
> > >>>---
> > >>
> > >>OK if I recall correctly the reason for reverting was that the fixes
> > >>Stefan was sending were broken and no access to hardware were the
> > >>issues would be visible. The reason for not doing anything til this
> > >>day is that we don't have T490 available.
> > >
> > >So as promised I have been in contact with Lenovo about this.
> > >
> > >Specifically I have been in contact with Lenovo about seeing an
> > >IRQ storm when the tpm_tis code tries to use the IRQ on a X1 carbon
> > >8th gen (X1C8), because of the now public plan that Lenovo will
> > >offer ordering this model with Fedora pre-installed:
> > >https://lwn.net/Articles/818595/
> > >
> > >On the X1C8 the problem has been diagnosed to be a misconfigured
> > >GPIO pin on the CPU (the SoC). The X1C8 uses an SPI connected
> > >TPM chip with its IRQ connected to a GPIO on the SoC which is
> > >configured in Direct IRQ mode, so that it directly asserts
> > >IRQs on one of the APIC IRQs.  The problem is that due to the
> > >misconfiguration as soon as the IRQ is enabled it fires
> > >continuously.
> > >
> > >For the X1C8 this should be fixed in the BIOS of the first
> > >batch which gets shipped out to customers so there we should
> > >not have to worry about this.
> > >
> > >It is likely (but not yet confirmed) that the issue on the T490
> > >is the same, although on my test X1C8 device I got an IRQ storm,
> > >followed by the kernel disabling the IRQ, not a non booting system.
> > >I guess this might be due to kernel configuration differences.
> > >
> > >Assuming that the issue on the T490 is the same, we might see a
> > >BIOS update fixing this, but given that non-booting is
> > >'not good ("tm")' even if there will be a BIOS fix we should
> > >still do something at the kernel level to also work with the
> > >older unfixed BIOS which is already out there.
> > >
> > >I've been thinking about this and I'm afraid that the only thing
> > >what we can do is add a DMI product-name (product-version for Lenovo)
> > >string based blacklist for IRQ usage to drivers/char/tpm/tpm_tis.c
> > >and set tpm_info.irq = -1 for devices on that list.
> > >
> > >My plan is to prepare a RFC patch of such a blacklist, while we
> > >wait for confirmation that the root cause on the T490 is the same
> > >as on the X1C8, but before I work on that I'm wondering if
> > >people agree that that is the best approach, or if there are
> > >other suggestions for dealing with this ?
> > >
> > >Regards,
> > >
> > >Hans
> > >
> >
> > Dan,
> >
> > Could this be the cause of the problem on the system you were
> > seeing the issue with, or was that using PTT?
> 
> It sounds similar, I'm just not immediately aware of where I can find
> out how the GPIOs are routed on that development board. I'll poke
> around.
> 
> What's PTT?

Intel fTPM.

/Jarkko