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

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Message-ID: <5d2f51a7.1c69fb81.6495.fbe8@mx.google.com>
Date:   Wed, 17 Jul 2019 09:49:42 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Alexander Steffen <Alexander.Steffen@...ineon.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     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

Quoting Jason Gunthorpe (2019-07-17 05:25:58)
> On Wed, Jul 17, 2019 at 02:00:06PM +0200, Alexander Steffen wrote:
> > On 17.07.2019 00:45, Stephen Boyd wrote:
> > > 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

Good point. I'll fix it.

> 
> 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
> 

Sometimes we have both drivers built-in. To maintain the tiny space
savings I'd prefer to just leave this as helpless and tristate.