linux-kernel - Re: [tpmdd-devel] [PATCH v1 12/12] tpm: TPM2 sysfs attributes

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Message-ID: <20140924185014.GA6801@intel.com>
Date:	Wed, 24 Sep 2014 21:50:14 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Stefan Berger <stefanb@...ux.vnet.ibm.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH v1 12/12] tpm: TPM2 sysfs attributes

On Wed, Sep 24, 2014 at 11:59:40AM -0600, Jason Gunthorpe wrote:
> On Wed, Sep 24, 2014 at 01:34:11PM -0400, Stefan Berger wrote:
> > On 09/24/2014 01:13 PM, Jason Gunthorpe wrote:
> > >On Wed, Sep 24, 2014 at 12:06:02PM +0300, Jarkko Sakkinen wrote:
> > >>+static ssize_t durations_show(struct device *dev, struct device_attribute *attr,
> > >>+			      char *buf)
> > >>+{
> > >>+	struct tpm_chip *chip = dev_get_drvdata(dev);
> > >>+
> > >>+	if (chip->vendor.duration[TPM_LONG] == 0)
> > >>+		return 0;
> > >>+
> > >>+	return sprintf(buf, "%d %d %d [%s]\n",
> > >>+		       jiffies_to_usecs(chip->vendor.duration[TPM_SHORT]),
> > >>+		       jiffies_to_usecs(chip->vendor.duration[TPM_MEDIUM]),
> > >>+		       jiffies_to_usecs(chip->vendor.duration[TPM_LONG]),
> > >>+		       chip->vendor.duration_adjusted
> > >>+		       ? "adjusted" : "original");
> > >>+}
> > >>+static DEVICE_ATTR_RO(durations);
> > >Seem useless since the durations are constant, drop it?
> > 
> > We show them for TPM 1.2 as well, so I'd keep them fo TPM2.
> 
> The durations are constant and hardwired in the driver for TPM2, and
> the sysfs file format does not follow the one-value-per-file
> rule.
> 
> So it doesn't display anything useful. In TPM2 mode all the timeouts
> are constant and known, so I'd rather see it go away.
> 
> > With all the problems we had with TPM 1.2 TPM's wrong timeouts and
> > showing them in sysfs, why not show them for TPM2 as well?
> 
> We had problems with devices reporting the wrong timeout from their
> cap queries - that isn't possible in TPM2.
> 
> Both of these values should live in debugfs anyhow.
> 
> It would be nice to start with a fresh set of correct sysfs files for
> TPM2, since essentially everything is different about the userspace
> interface we can safely make a breaking change here.

I'll drop timeouts and durations. It's easy to add them later if they
are needed.

> Jason

/Jarkko
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