linux-kernel - Re: [PATCH 1/5] tpm: add functions to set and unset the tpm chips reset state

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Date:   Sun, 10 Apr 2022 11:03:01 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     peterhuewe@....de, jarkko@...nel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, stefanb@...ux.ibm.com,
        p.rosenberger@...bus.com, lukas@...ner.de
Subject: Re: [PATCH 1/5] tpm: add functions to set and unset the tpm chips
 reset state


Hi,

On 07.04.22 at 16:25, Jason Gunthorpe wrote:
> On Thu, Apr 07, 2022 at 01:18:45PM +0200, Lino Sanfilippo wrote:
>> Currently it is not possible to set the tpm chips reset state from within
>> the driver. This is problematic if the chip is still in reset after the
>> system comes up. This may e.g. happen if the reset line is pulled into
>> reset state by a pin configuration in the device tree.
>
> This kind of system is badly misdesigned.
>
> TPM PCRs fundementally cannot work if the TPM reset line is under
> software control.
>
> Jason
>


you may be right about the misdesign, but as a matter of fact
there are systems which have the TPMs reset line connected to a GPIO and not
the system reset. For those systems we should provide a way to let at least the
driver put the TPM out of reset (note that on those systems the TPM reset can
be triggered by software anyway by asserting/deasserting the GPIO line).


Regards,
Lino