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

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Date:   Thu, 18 Jul 2019 18:47:22 +0200
From:   Alexander Steffen <Alexander.Steffen@...ineon.com>
To:     Stephen Boyd <swboyd@...omium.org>,
        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

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.

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?

Alexander