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

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Date:   Fri, 9 Nov 2018 21:37:48 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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?
As it was said, need to request locality and relinquish it for each command, I believe thought this is not required for client platforms only for servers. 
> 
> > 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?
If I'm reading this patch correctly you do cmd_ready when tpm is opened, it doesn't mean there is a real traffic, so why to keep it awake. 
Thanks
Tomas