On 6/25/20 1:28 PM, Jason Gunthorpe wrote:

On Thu, Jun 25, 2020 at 10:56:43AM -0400, Stefan Berger wrote:

quoted

Hello!

  I want to enable IRQs now in QEMU's TPM TIS device model and I need to work
with the following patch to Linux TIS. I am wondering whether the changes
there look reasonable to you? Windows works with the QEMU modifications
as-is, so maybe it's a bug in the TIS code (which I had not run into
before).


The point of the loop I need to introduce in the interrupt handler is that
while the interrupt handler is running another interrupt may occur/be posted
that then does NOT cause the interrupt handler to be invoked again but
causes a stall, unless the loop is there.

That seems like a qemu bug, TPM interrupts are supposed to be level
interrupts, not edge.

Following this document here the hardware may choose to support 
different types of interrutps:

https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p04_r0p37_pub-1.pdf

Table 23. Edge falling or rising, level low or level high.

So with different steps in the driver causing different types of 
interrupts, we may get into such situations where we process some 
interrupt 'reasons' but then another one gets posted, I guess due to 
parallel processing.

   Stefan