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

[Jerry Snitselaar <jsnitsel@redhat.com>]

On Thu May 07 20, 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?
>

PTT is Intel's firmware based TPM.

>My concern with a blacklist is that the existing tpm_tis module
>parameter to disable interrupts, IIRC, did not help mitigate this
>problem. So I would think that if there is a blackilst it should at
>least be amenable by module parameter for new platforms, or that
>specifying "interrupts=0" to tpm_tis.ko behaves identically to the
>device being placed on the list.
>