On Tue, Nov 24, 2020 at 10:10:21AM -0800, James Bottomley wrote: > On Tue, 2020-11-24 at 10:52 -0700, Jerry Snitselaar wrote: > > Before diving further into that though, does anyone else have an > > opinion on ripping out the irq code, and just using polling? We've > > been only polling since 2015 anyways. > > Well only a biased one, obviously: polling causes large amounts of busy > waiting, which is a waste of CPU resources and does increase the time > it takes us to do TPM operations ... not a concern if you're doing long > computation ones, like signatures, but it is a problem for short > operations like bulk updates of PCRs. The other potential issue, as we > saw with atmel is that if you prod the chip too often (which you have > to do with polling) you risk upsetting it. We've spent ages trying to > tune the polling parameters to balance reduction of busy wait with chip > upset and still, apparently, not quite got it right. If the TPM has a > functioning IRQ then it gets us out of the whole polling mess entirely. > The big question is how many chips that report an IRQ actually have a > malfunctioning one? > > James Do we have a way to know is Windows TPM code using IRQ's? /Jarkko
