linux-kernel - Re: [PATCH] tpm: Add explicit chip->ops locking for sysfs attributes.

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Date:   Tue, 21 Nov 2017 10:28:58 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Peter Huewe <peterhuewe@....de>,
        Andrey Pronin <apronin@...omium.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Add explicit chip->ops locking for sysfs attributes.

On Tue, Nov 21, 2017 at 01:49:47AM +0200, Jarkko Sakkinen wrote:
> On Mon, Nov 20, 2017 at 04:17:28PM -0700, Jason Gunthorpe wrote:
> > On Mon, Nov 20, 2017 at 02:45:23PM -0800, Guenter Roeck wrote:
> > 
> > > "tpm: Enable sysfs support for TPM2 devices
> > > 
> > > Access to chip->ops on TPM2 devices requires an explicit lock,
> > > since the pointer is set to NULL in tpm_class_shutdown().
> > > Implement that lock for sysfs access functions and enable sysfs
> > > support for TPM2 devices."
> > 
> > Wait.. one of the reasons we let it go with no sysfs for so long was
> > because there was not many sysfs files that were compatible with tpm2?
> > 
> > For TPM2 we have sort of had an API break of sorts from TPM1 in a
> > couple places around sysfs, and I would like to not re-introduce any
> > badly designed sysfs files for TPM2..
> > 
> > So.. When you apply this patch, what changes actually happen in the
> > sysfs directory?
> > 
> > Jason
> 
> Oops. I was too quick. This will cause all the TPM 1.x attributes
> added also for TPM 2.0. That's not a great idea. The tpm_dev_group
> should be only assigned for TPM 1.x devices. This commit should only
> enable addition of sysfs attributes for TPM 2.0 devices.
> 

After having a closer look, I agree. Sorry for my naivite.

I'll split the patch into two parts, and only add (hopefully)
non-controversial tpm2 attributes for now (which I think is durations
and timeouts). Or, in other words, I'll split the attributes into
two groups - one generic and one for tpm1.

Thanks,
Guenter