linux-kernel - Re: [PATCH v4 4/6] tpm: tpm_tis_spi: Export functionality to other drivers

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Date:   Mon, 19 Aug 2019 19:40:05 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        Andrey Pronin <apronin@...omium.org>,
        Duncan Laurie <dlaurie@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <groeck@...omium.org>,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH v4 4/6] tpm: tpm_tis_spi: Export functionality to other
 drivers

On Mon, Aug 12, 2019 at 03:36:20PM -0700, Stephen Boyd wrote:
> Export a new function, tpm_tis_spi_init(), and the associated
> read/write/transfer APIs so that we can create variant drivers based on
> the core functionality of this TPM SPI driver. Variant drivers can wrap
> the tpm_tis_spi_phy struct with their own struct and override the
> behavior of tpm_tis_spi_transfer() by supplying their own flow control
> and pre-transfer hooks. This shares the most code between the core
> driver and any variants that want to override certain behavior without
> cluttering the core driver.

I think this is adding way too much complexity for the purpose. We
definitely do want this three layer architecture here.

Instead there should be a single tpm_tis_spi driver that dynamically
either TCG or CR50. I rather take some extra bytes in the LKM than
the added complexity.

/Jarkko