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

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

On Thu, Jun 04, 2020 at 02:17:12AM -0700, Jerry Snitselaar 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
> > 
> 
> Jarrko,
> 
> Any thoughts about how we should move forward on dealing with this?
> I've got a report about the original problem Stefan was dealing with,
> where the tpm isn't powered on when it tries to send a command to
> generate an interrupt. The tpm is functioning so it isn't urgent,
> but it would be good to get this cleaned up so users aren't getting
> transmit errors and firmware bug messages. Hans did you make any
> progress on the blacklist patch?

We need the blacklist. Up until that warnings is the best we can do.

/Jarkko