linux-kernel - Re: [PATCH v2 5/6] tpm: add driver for cr50 on SPI

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Date:   Wed, 17 Jul 2019 09:25:58 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alexander Steffen <Alexander.Steffen@...ineon.com>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Andrey Pronin <apronin@...omium.org>,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org,
        Duncan Laurie <dlaurie@...omium.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH v2 5/6] tpm: add driver for cr50 on SPI

On Wed, Jul 17, 2019 at 02:00:06PM +0200, Alexander Steffen wrote:
> On 17.07.2019 00:45, 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.
> > 
> > Signed-off-by: Andrey Pronin <apronin@...omium.org>
> > [swboyd@...omium.org: Replace boilerplate with SPDX tag, drop
> > suspended bit and remove ifdef checks in cr50.h, push tpm.h
> > include into cr50.c]
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> >   drivers/char/tpm/Kconfig    |  16 ++
> >   drivers/char/tpm/Makefile   |   2 +
> >   drivers/char/tpm/cr50.c     |  33 +++
> >   drivers/char/tpm/cr50.h     |  15 ++
> >   drivers/char/tpm/cr50_spi.c | 450 ++++++++++++++++++++++++++++++++++++
> >   5 files changed, 516 insertions(+)
> >   create mode 100644 drivers/char/tpm/cr50.c
> >   create mode 100644 drivers/char/tpm/cr50.h
> >   create mode 100644 drivers/char/tpm/cr50_spi.c
> > 
> > diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> > index 88a3c06fc153..b7028bfa6f87 100644
> > +++ b/drivers/char/tpm/Kconfig
> > @@ -114,6 +114,22 @@ config TCG_ATMEL
> >   	  will be accessible from within Linux.  To compile this driver
> >   	  as a module, choose M here; the module will be called tpm_atmel.
> > +config TCG_CR50
> > +	bool
> > +	---help---
> > +	  Common routines shared by drivers for Cr50-based devices.
> > +
> 
> Is it a common pattern to add config options that are not useful on their
> own? When would I ever enable TCG_CR50 without also enabling TCG_CR50_SPI?
> Why can't you just use TCG_CR50_SPI for everything?

This is an internal kconfig symbol, it isn't seen by the user, which
is a pretty normal pattern.

But I don't think the help should be included (since it cannot be
seen), and I'm pretty sure it should be a tristate

But overall, it might be better to just double link the little helper:

obj-$(CONFIG_TCG_CR50_SPI) += cr50.o cr50_spi.o
obj-$(CONFIG_TCG_CR50_I2C) += cr50.o cr50_i2c.o

As we don't actually ever expect to load both modules into the same
system

Jason