On Fri, Aug 16, 2019 at 7:12 PM Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx> wrote: > > On 15.08.2019 19:03, Oshri Alkobi wrote: > > On Thu, Jul 18, 2019 at 8:10 PM Alexander Steffen > > <Alexander.Steffen@xxxxxxxxxxxx> wrote: > >> > >> On 18.07.2019 14:51, Eyal.Cohen@xxxxxxxxxxx wrote: > >>> Hi Jarkko and Alexander, > >>> > >>> We have made an additional code review on the TPM TIS core driver, it looks quite good and we can connect our new I2C driver to this layer. > >> > >> Great :) In the meantime, I've done some experiments creating an I2C > >> driver based on tpm_tis_core, see > >> https://patchwork.kernel.org/patch/11049363/ Please have a look at that > >> and provide your feedback (and/or use it as a basis for further > >> implementations). > >> > > > > Sorry for the late response. > > > > Thanks Alexander, indeed it looks much simpler. > > I've checked it with Nuvoton's TPM - basic TPM commands work > > Nice :) > > > I only > > had to remove the first msg from the read/write I2C transmitting > > (from/to TPM_LOC_SEL), the TPM couldn't handle two register writes in > > a sequence. > > Actually it is more efficient to set TPM_LOC_SEL only before locality > > check/request/relinquish - it is sticky. > > There is one problem though: Do we assume that only the kernel driver > will communicate with the TPM or might there be something else that also > talks to the TPM? > > If it is only the kernel driver, we could probably skip setting > TPM_LOC_SEL at all, since it defaults to 0 and the driver will never use > anything else. If something else does its own I2C communication with the > TPM, it might write different values to TPM_LOC_SEL at any time, causing > the kernel driver to use a different locality than intended. This was > the reason I always set TPM_LOC_SEL within the same transaction. > > > I still didn't manage to work with interrupts, will debug it. > > Interrupt support might be broken in general at the moment, see this > thread: https://www.spinics.net/lists/linux-integrity/msg08663.html > > > We weren't aware to the implementation of Christophe/ST which looks > > good and can be complement to yours. > > If no one is currently working on that, we can prepare a new patch > > that is based on both. > > Please let us know. > > I won't have the time to do anything, at least for the next two weeks, > so feel free to pick it up. > Great, we will start working on it. > >>> However, there are several differences between the SPI interface and the I2C interface that will require changes to the TIS core. > >>> At a minimum we thought of: > >>> 1. Handling TPM Localities in I2C is different > >> > >> It turned out not to be that different in the end, see the code > >> mentioned above and my comment here: > >> https://patchwork.kernel.org/cover/11049365/ > >> > >>> 2. Handling I2C CRC - relevant only to I2C bus hence not supported today by TIS core > >> > >> That is completely optional, so there is no need to implement it in the > >> beginning. Also, do you expect a huge benefit from that functionality? > >> Are bit flips that much more likely on I2C compared to SPI, which has no > >> CRC at all, but still works fine? > >> > > > > I2C is noisy bus with potentially more devices with larger variety > > than SPI. I2C may have more than one master and may have collisions > > and/or arbitration. > > If multi-master usage is a concern, there are probably a lot more places > in the driver that need to be adapted to deal with concurrent > access/data corruption. For now, I'd assume a single master, similar to SPI. > > Alexander Oshri
