linux-kernel - Re: [PATCH v2 0/2] char: tpm: add new driver for tpm i2c ptp

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Message-ID: <2e2e646c3fae87307a149ee06e9fd4a7e493830d.camel@linux.intel.com>
Date:   Fri, 05 Jul 2019 14:15:37 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Alexander Steffen <Alexander.Steffen@...ineon.com>,
        Oshri Alkoby <oshrialkoby85@...il.com>, robh+dt@...nel.org,
        mark.rutland@....com, peterhuewe@....de, jgg@...pe.ca,
        arnd@...db.de, gregkh@...uxfoundation.org, oshri.alkoby@...oton.com
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org, gcwilson@...ibm.com,
        kgoldman@...ibm.com, nayna@...ux.vnet.ibm.com,
        dan.morav@...oton.com, tomer.maimon@...oton.com
Subject: Re: [PATCH v2 0/2] char: tpm: add new driver for tpm i2c ptp

On Thu, 2019-07-04 at 13:29 +0200, Alexander Steffen wrote:
> On 04.07.2019 10:43, Jarkko Sakkinen wrote:
> > Check out tpm_tis_core.c and tpm_tis_spi.c. TPM TIS driver implements
> > that spec so you should only implement a new physical layer.
> 
> I had the same thought. Unfortunately, the I2C-TIS specification 
> introduces two relevant changes compared to tpm_tis/tpm_tis_spi:

I doubt that there was any comparison made.

> 1. Locality is not encoded into register addresses anymore, but stored 
> in a separate register.
> 2. Several register addresses have changed (but still contain compatible 
> contents).
> 
> I'd still prefer not to duplicate all the high-level logic from 
> tpm_tis_core. But this will probably mean to introduce some new 
> interfaces between tpm_tis_core and the physical layers.

Agreed. Some plumbing needs to be done in tpm_tis_core to make it work
for this. We definitely do not want to duplicate code that has been
field tested for years.

> Also, shouldn't the new driver be called tpm_tis_i2c, to group it with 
> all the other (TIS) drivers, that implement a vendor-independent 
> protocol? With tpm_i2c_ptp users might assume that ptp is just another 
> vendor.

Yes, absolutely. I guess the driver has been done without looking at
what already exist in the TPM kernel stack.

/Jarkko