On Tue, Mar 12, 2019 at 07:42:46AM -0700, James Bottomley wrote: > On Tue, 2019-03-12 at 14:50 +0200, Jarkko Sakkinen wrote: > > On Mon, Mar 11, 2019 at 05:27:43PM -0700, James Bottomley wrote: > > > On Mon, 2019-03-11 at 16:54 -0700, Calvin Owens wrote: > > > > e're having lots of problems with TPM commands timing out, and > > > > we're seeing these problems across lots of different hardware > > > > (both v1/v2). > > > > > > > > I instrumented the driver to collect latency data, but I wasn't > > > > able to find any specific timeout to fix: it seems like many of > > > > them are too aggressive. So I tried replacing all the timeout > > > > logic with a single universal long timeout, and found that makes > > > > our TPMs 100% reliable. > > > > > > > > Given that this timeout logic is very complex, problematic, and > > > > appears to serve no real purpose, I propose simply deleting all > > > > of it. > > > > > > "no real purpose" is a bit strong given that all these timeouts are > > > standards mandated. The purpose stated by the standards is that > > > there needs to be a way of differentiating the TPM crashed from the > > > TPM is taking a very long time to respond. For a normally > > > functioning TPM it looks complex and unnecessary, but for a > > > malfunctioning one it's a lifesaver. > > > > Standards should be only followed when they make practical sense and > > ignored when not. The range is only up to 2s anyway. > > I don't disagree ... and I'm certainly not going to defend the TCG > because I do think the complexity of some of its standards contributed > to the lack of use of TPM 1.2. > > However, I am saying we should root cause this problem rather than take > a blind shot at the apparent timeout complexity. My timeout > instability is definitely related to the polling adjustments, so it's > not unreasonable to think Facebooks might be as well. Yeah, referring to my review comment, I think the very first thing that should be done is to split patch into two. Then we can probably give better feedback. /Jarkko
