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. James
