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Subject: Re: [PATCH v2 5/6] tpm: add driver for cr50 on SPI
To:     Stephen Boyd <swboyd@chromium.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Peter Huewe <peterhuewe@gmx.de>
CC:     Andrey Pronin <apronin@chromium.org>,
        <linux-kernel@vger.kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <linux-integrity@vger.kernel.org>,
        Duncan Laurie <dlaurie@chromium.org>,
        Guenter Roeck <groeck@chromium.org>
References: <20190716224518.62556-1-swboyd@chromium.org>
 <20190716224518.62556-6-swboyd@chromium.org>
 <f824e3ab-ae2f-8c2f-549a-16569b10966e@infineon.com>
 <5d2f7daf.1c69fb81.c0b13.c3d4@mx.google.com>
 <5d2f955d.1c69fb81.35877.7018@mx.google.com>
 <b05904bf-00b9-bf30-0fc9-9f363e181d80@infineon.com>
 <5d30b649.1c69fb81.f440e.9a0a@mx.google.com>
From:   Alexander Steffen <Alexander.Steffen@infineon.com>
Message-ID: <1bb8d417-3199-7aff-ad60-b25464502cb3@infineon.com>
Date:   Fri, 19 Jul 2019 09:53:00 +0200
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On 18.07.2019 20:11, Stephen Boyd wrote:
> 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.

Sure, I'd expect Jarkko will say something once he's back from vacation.

Alexander