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

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Date:   Wed, 17 Jul 2019 14:12:16 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Alexander Steffen <Alexander.Steffen@...ineon.com>,
        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 10:05:52AM -0700, Stephen Boyd wrote:
> Quoting Jason Gunthorpe (2019-07-17 09:56:28)
> > On Wed, Jul 17, 2019 at 09:49:42AM -0700, Stephen Boyd wrote:
> > > 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:
> > > > 
> > > > 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.
> > 
> > If it is builtin you only get one copy of cr50.o anyhow. The only
> > differences is for modules, then the two modules will both be a bit
> > bigger instead of a 3rd module being created
> > 
> 
> Yes. The space savings comes from having the extra module 'cr50.ko' that
> holds almost nothing at all when the two drivers are modules.

I'm not sure it is an actual savings, there is alot of minimum
overhead and alignment to have a module in the first place.

Jason