On Wed, Sep 30, 2020 at 03:31:20PM -0700, James Bottomley wrote: > On Thu, 2020-10-01 at 00:09 +0300, Jarkko Sakkinen wrote: > > On Wed, Sep 30, 2020 at 01:48:15PM -0700, James Bottomley wrote: > > > On Wed, 2020-09-30 at 18:37 +0300, Jarkko Sakkinen wrote: > > > > On Wed, Sep 30, 2020 at 07:54:58AM -0700, James Bottomley wrote: > > > > > On Wed, 2020-09-30 at 05:16 +0300, Jarkko Sakkinen wrote: > > > > > > On Mon, Sep 28, 2020 at 03:11:39PM -0700, James Bottomley > > > > > > wrote: > > > > > > > On Sun, 2020-09-27 at 22:59 -0700, Hao Wu wrote: > > > > > > > [...] > > > > > > > > > However, there is another possibility: it's something > > > > > > > > > to do > > > > > > > > > with the byte read; I notice you don't require the same > > > > > > > > > slowdown for the burst count read, which actually reads > > > > > > > > > the > > > > > > > > > status register and burst count as a read32. If that > > > > > > > > > really is the case, for the atmel would substituting a > > > > > > > > > read32 and just throwing the upper bytes away in > > > > > > > > > tpm_tis_status() allow us to keep the current > > > > > > > > > timings? I > > > > > > > > > can actually try doing this and see if it fixes my > > > > > > > > > nuvoton. > > > > > > > > > > > > > > > > If would be helpful if you can find the solution without > > > > > > > > reducing performance. I think it is a separate problem to > > > > > > > > address though. Maybe not worth to mix them in the same > > > > > > > > fix. > > > > > > > > > > > > > > Well, if it works, no other fix is needed. > > > > > > > > > > > > > > This is what I'm currently trying out on my nuvoton with > > > > > > > the > > > > > > > timings reverted to being those in the vanilla kernel. So > > > > > > > far > > > > > > > it hasn't crashed, but I haven't run it for long enough to > > > > > > > be > > > > > > > sure yet. > > > > > > > > > > > > > > James > > > > > > > > > > > > OK, so the bus does not like one byte reads but prefers full > > > > > > (32- > > > > > > bit) word reads? I.e. what's the context? > > > > > > > > > > It's not supported by anything in the spec just empirical > > > > > observation. However, the spec says the status register is 24 > > > > > bits: the upper 16 being the burst count. When we read the > > > > > whole > > > > > status register, including the burst count, we do a read32. I > > > > > observed that the elongated timing was only added for the read8 > > > > > code not the read32 which supports the theory that the former > > > > > causes the Atmel to crash but the latter doesn't. Of course > > > > > it's > > > > > always possible that probabilistically the Atmel is going to > > > > > crash > > > > > on the burst count read, but that's exercised far less than the > > > > > status only read. > > > > > > > > This paragraph is good enough explanation for me. Can you include > > > > it > > > > to the final commit as soon as we hear how your fix works for > > > > Hao? > > > > > > Sure. I'm afraid I have to report that it didn't work for me. My > > > Nuvoton is definitely annoyed by the frequency of the prodding > > > rather > > > than the register width. > > > > Sorry, this might have been stated at some point but what type of bus > > is it connected with? > > It's hard to tell: this is my Dell Laptop, but I'd have to bet LPC. > > > Does it help in any way to tune the frequency? > > Of the bus? We simply don't have access: a TIS TPM is projected at a > specific memory mapped address and all the conversion to the LPC back > end is done by memory read/write operations. The TPM itself has a > clock but doesn't give the TIS interface software control. Some TPM's use tpm_tis_spi instead of MMIO. > > I also wonder if we could adjust the frequency dynamically. I.e. > > start with optimistic value and lower it until finding the sweet > > spot. > > The problem is the way this crashes: the TPM seems to be unrecoverable. > If it were recoverable without a hard reset of the entire machine, we > could certainly play around with it. I can try alternative mechanisms > to see if anything's viable, but to all intents and purposes, it looks > like my TPM simply stops responding to the TIS interface. A quickly scraped idea probably with some holes in it but I was thinking something like 1. Initially set slow value for latency, this could be the original 15 ms. 2. Use this to read TPM_PT_VENDOR_STRING_*. 3. Lookup based vendor string from a fixup table a latency that works (the fallback latency could be the existing latency). 4. Set the legit latency. /Jarkko
