linux-kernel - Re: [PATCH v5 16/17] tpm: take TPM chip power gating out of tpm

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Message-ID: <20181108230700.GA8038@linux.intel.com>
Date:   Fri, 9 Nov 2018 01:07:00 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Winkler, Tomas" <tomas.winkler@...el.com>
Cc:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        "Struk, Tadeusz" <tadeusz.struk@...el.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 16/17] tpm: take TPM chip power gating out of
 tpm_transmit()

On Thu, Nov 08, 2018 at 06:38:59PM +0000, Winkler, Tomas wrote:
> > Call tpm_chip_start() and tpm_chip_stop() in
> > 
> > * tpm_try_get_ops() and tpm_put_ops()
> > * tpm_chip_register()
> > * tpm2_del_space()
> > 
> > And remove these calls from tpm_transmit(). The core reason for this change
> > is that in tpm_vtpm_proxy a locality change requires a virtual TPM command
> > (a command made up just for that driver).
> > 
> I don't think you can do that,  locality has to be request for each
> command, as  for example tboot can request higher locality any time.

That could be a potential problem. How tboot intervention gets prevented
without this patch?

> Same for cmd_ready()/go_idle() powergatin, you will prevent the whole
> platform entering power save state.

Why would you want that in a middle of using the TPM anyway?

> Thanks
> Tomas

/Jarkko