Re: [PATCH 1/3] tpm/tpm_crb: implement tpm crb idle state

[Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Wed, Sep 07, 2016 at 10:15:48AM -0600, Jason Gunthorpe wrote:
> On Wed, Sep 07, 2016 at 02:32:31PM +0300, Tomas Winkler wrote:
> > The register TPM_CRB_CTRL_REQ_x contains bits goIdle and cmdReady for
> > SW to indicate that the device can enter or should exit the idle state.
> > 
> > The legacy ACPI-start (SMI + DMA) based devices do not support these
> > bits and the idle state management is not exposed to the host SW.
> > Thus, this functionality only is enabled only for a CRB start (MMIO)
> > based devices.
> > 
> > We introduce two new callbacks for command ready and go idle for TPM CRB
> > device which are called across TPM transactions.
> 
> Jarkko and I have been talking about higher level locking (eg to
> sequence a series of operations) it might make more sense to move the
> power management up to that layer. No sense in going to idle mode if
> we know another command is about to come.

Maybe if TIS/FIFO driver have similar feature in future we can
generalize but I generally like bottom up approach. Do things first
at the low level and bump them up when it starts to make sense.

I think right now what this patch set contains is sufficient from
performance perspetice even if goToIdle is done for every transaction
given the workloads. We can improve from this later on by using PM
runtime framework and its autosuspend feature.

Does this sound fair?

/Jarkko

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