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

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Message-ID: <5d30b649.1c69fb81.f440e.9a0a@mx.google.com>
Date:   Thu, 18 Jul 2019 11:11:20 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Alexander Steffen <Alexander.Steffen@...ineon.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Peter Huewe <peterhuewe@....de>
Cc:     Andrey Pronin <apronin@...omium.org>, linux-kernel@...r.kernel.org,
        Jason Gunthorpe <jgg@...pe.ca>, 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 Alexander Steffen (2019-07-18 09:47:22)
> On 17.07.2019 23:38, Stephen Boyd wrote:
> > Quoting Stephen Boyd (2019-07-17 12:57:34)
> >> Quoting Alexander Steffen (2019-07-17 05:00:06)
> >>>
> >>> Can't the code be shared more explicitly, e.g. by cr50_spi wrapping
> >>> tpm_tis_spi, so that it can intercept the calls, execute the additional
> >>> actions (like waking up the device), but then let tpm_tis_spi do the
> >>> common work?
> >>>
> >>
> >> I suppose the read{16,32} and write32 functions could be reused. I'm not
> >> sure how great it will be if we combine these two drivers, but I can
> >> give it a try today and see how it looks.
> >>
> > 
> > Here's the patch. I haven't tested it besides compile testing.

The code seems to work but I haven't done any extensive testing besides
making sure that the TPM responds to pcr reads and some commands like
reading random numbers.

> 
> Thanks for providing this. Makes it much easier to see what the actual 
> differences between the devices are.
> 
> Do we have a general policy on how to support devices that are very 
> similar but need special handling in some places? Not duplicating the 
> whole driver just to change a few things definitely seems like an 
> improvement (and has already been done in the past, as with 
> TPM_TIS_ITPM_WORKAROUND). But should all the code just be added to 
> tpm_tis_spi.c? Or is there some way to keep a clearer separation, 
> especially when (in the future) we have multiple devices that all have 
> their own set of deviations from the spec?
> 

If you have any ideas on how to do it please let me know. At this point,
I'd prefer if the maintainers could provide direction on what they want.