linux-kernel - Re: [tpmdd-devel] [PATCH] tpm: do not suspend/resume if power stays on

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Date:   Wed, 1 Mar 2017 14:39:09 -0800
From:   Sonny Rao <sonnyrao@...omium.org>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [PATCH] tpm: do not suspend/resume if power stays on

On Wed, Mar 1, 2017 at 10:43 AM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
>> > +Optional properties:
>> > +- powered-while-suspended: present when the TPM is left powered on between
>> > +  suspend and resume (makes the suspend/resume callbacks do nothing).
>>
>> This reads like configuration rather than a HW property.
>
> I read this to mean the HW does not cut power to the TPM when Linux
> does 'suspend'.

That's correct, it is a hardware property describing whether power is
removed during suspend.

>
> We recently added global suspend/resume callbacks to the TPM
> core. Those call backs do not power off the TPM, they just prepare its
> internal state to loose power to the chip. Skipping that process on
> hardware that does not power-off the TPM makes sense to me.
>
> But, Sonny, perhaps this should be a global flag in tpm_chip, not a
> per-interface-driver override?

It's a property of the board design not the chip -- maybe I'm misunderstanding?

>
> Jason