linux-kernel - Re: [PATCH v6 4/4] tpm: tpm_tis

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Date:   Tue, 03 Sep 2019 09:52:07 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Peter Huewe <peterhuewe@....de>
Cc:     Andrey Pronin <apronin@...omium.org>, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.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>,
        Heiko Stuebner <heiko@...ech.de>
Subject: Re: [PATCH v6 4/4] tpm: tpm_tis_spi: Support cr50 devices

Quoting Jarkko Sakkinen (2019-09-03 09:39:51)
> On Thu, 2019-08-29 at 15:41 -0700, Stephen Boyd wrote:
> > From: Andrey Pronin <apronin@...omium.org>
> > 
> > Add TPM2.0 PTP FIFO compatible SPI interface for chips with Cr50
> > firmware. The firmware running on the currently supported H1 Secure
> > Microcontroller requires a special driver to handle its specifics:
> > 
> >  - need to ensure a certain delay between SPI transactions, or else
> >    the chip may miss some part of the next transaction
> >  - if there is no SPI activity for some time, it may go to sleep,
> >    and needs to be waken up before sending further commands
> >  - access to vendor-specific registers
> > 
> > Cr50 firmware has a requirement to wait for the TPM to wakeup before
> > sending commands over the SPI bus. Otherwise, the firmware could be in
> > deep sleep and not respond. The method to wait for the device to wakeup
> > is slightly different than the usual flow control mechanism described in
> > the TCG SPI spec. Add a completion to tpm_tis_spi_transfer() before we
> > start a SPI transfer so we can keep track of the last time the TPM
> > driver accessed the SPI bus to support the flow control mechanism.
> > 
> > Split the cr50 logic off into a different file to keep it out of the
> > normal code flow of the existing SPI driver while making it all part of
> > the same module when the code is optionally compiled into the same
> > module. Export a new function, tpm_tis_spi_init(), and the associated
> > read/write/transfer APIs so that we can do this. Make the cr50 code wrap
> > the tpm_tis_spi_phy struct with its own struct to override the behavior
> > of tpm_tis_spi_transfer() by supplying a custom flow control hook. This
> > shares the most code between the core driver and the cr50 support
> > without combining everything into the core driver or exporting module
> > symbols.
> > 
> > Signed-off-by: Andrey Pronin <apronin@...omium.org>
> > Cc: Andrey Pronin <apronin@...omium.org>
> > Cc: Duncan Laurie <dlaurie@...omium.org>
> > Cc: Jason Gunthorpe <jgg@...pe.ca>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Guenter Roeck <groeck@...omium.org>
> > Cc: Alexander Steffen <Alexander.Steffen@...ineon.com>
> > Cc: Heiko Stuebner <heiko@...ech.de>
> 
> Had to time to look at this patch set after all before LPC. I just
> realized that the kconfig has taken away. Not sure why is that
> because there's been only request to not have a new LKM. There
> still should be ability opt-out to have Cr50 support in vmlinux.
> 

That's fair. I'll put the Kconfig option back. There's still the small
issue of what to do about the module name. Should I rename the
tpm_tis_spi.c file to something else so that the module can keep the
same name? Or was the tpm_tis_spi_mod.ko trick from v5 good enough?