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

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Date:   Fri, 19 Jul 2019 09:51:16 +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 18.07.2019 20:07, Stephen Boyd wrote:
> Quoting Alexander Steffen (2019-07-18 09:47:14)
>> On 17.07.2019 21:57, Stephen Boyd wrote:
>>>
>>> I think the idea is to let users override the quality if they decide
>>> that they don't want to use the default value specified in the driver.
>>
>> But isn't this something that applies to all TPMs, not only cr50? So
>> shouldn't this parameter be added to one of the global modules (tpm?
>> tpm_tis_core?) instead? Or do all low-level drivers (tpm_tis,
>> tpm_tis_spi, ...) need this parameter to provide a consistent interface
>> for the user?
> 
> Looking at commit 7a64c5597aa4 ("tpm: Allow tpm_tis drivers to set hwrng
> quality.") I think all low-level drivers need to set the hwrng quality
> somehow. I'm not sure how tpm_tis_spi will do that in general, but at
> least for cr50 we have derived this quality number.
> 
> I can move this module parameter to tpm_tis_core.c, but then it will be
> a global hwrng quality override for whatever tpm is registered through
> tpm_tis_core instead of per-tpm driver. This is sort of a problem right
> now too if we have two tpm_tis_spi devices. I can drop this parameter if
> you want.

Since it does not seem like a critical feature, maybe just drop it for 
now. Then we can figure out a way to do it properly and add it later.

Alexander