RE: [PATCH v2 0/2] char: tpm: add new driver for tpm i2c ptp

[Benoit HOUYERE <benoit.houyere@st.com>]

Hi Alexander, Jarkko and Eyal,

A first I2C TCG patch (tpm_tis_i2c.c) has been proposed in the same time as tpm_tis_spi.c by Christophe 3 years ago.

https://patchwork.kernel.org/patch/8628681/

At the time, we have had two concerns :
	1) I2C TPM component number, in the market, compliant with new I2C TCG specification to validate new I2C driver.
	2) Lots changing  was already provided by tpm_tis_spi.c on 4.8.

That's why Tpm_tis_i2c.c has been postponed.

Tpm_tis_spi Linux driver is now robust, if we have several different I2C TPM solutions today to validate a tpm_tis_i2c driver, I 'm ready to contribute to it for validation (STmicro TPM) or propose a solution compatible on 5.1 linux driver if needed under timeframe proposed (second half of august).

Best Regards,

Benoit



-----Original Message-----
From: linux-integrity-owner@vger.kernel.org <linux-integrity-owner@vger.kernel.org> On Behalf Of Alexander Steffen
Sent: jeudi 18 juillet 2019 19:10
To: Eyal.Cohen@nuvoton.com; jarkko.sakkinen@linux.intel.com; tmaimon77@gmail.com
Cc: oshrialkoby85@gmail.com; robh+dt@kernel.org; mark.rutland@arm.com; peterhuewe@gmx.de; jgg@ziepe.ca; arnd@arndb.de; gregkh@linuxfoundation.org; oshri.alkoby@nuvoton.com; devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-integrity@vger.kernel.org; gcwilson@us.ibm.com; kgoldman@us.ibm.com; nayna@linux.vnet.ibm.com; Dan.Morav@nuvoton.com; oren.tanami@nuvoton.com
Subject: Re: [PATCH v2 0/2] char: tpm: add new driver for tpm i2c ptp

On 18.07.2019 14:51, Eyal.Cohen@nuvoton.com 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).

> 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?

> 3. Handling Chip specific issues, since I2C implementation might be 
> slightly different across the various TPM vendors

Right, that seems similar to the cr50 issues (https://lkml.org/lkml/2019/7/17/677), so there should probably be a similar way to do it.

> 4. Modify tpm_tis_send_data and tpm_tis_recv_data to work according 
> the TCG Device Driver Guide (optimization on TPM_STS access and 
> send/recv retry)

Optimizations are always welcome, but I'd expect basic communication to work already with the current code (though maybe not as efficiently as possible).

> Besides this, during development we might encounter additional differences between SPI and I2C.
> 
> We currently target to allocate an eng. to work on this on the second half of August with a goal to have the driver ready for the next kernel merge window.
> 
> Regards,
> Eyal.