Hi,

On 10/16/20 12:39 AM, Matthew Garrett wrote:

On Thu, Oct 15, 2020 at 2:44 PM Jerry Snitselaar [off-list ref] wrote:

quoted

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.

IIRC then at least on the T490 the irq storm caused systems to not boot
in some cases. I guess if we detect the storm and disable the irq we might
fix that... OTOH this problem seems to only hit a certain generation of
Thinkpads so with some luck the denylist should not be too big and the denylist
approach should work.

Regards,

Hans