linux-kernel - Re: [PATCH 2/2] platform/x86: Add Intel Software Defined Silicon driver

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Date:   Mon, 27 Sep 2021 10:53:09 -0700
From:   "David E. Box" <david.e.box@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     lee.jones@...aro.org, hdegoede@...hat.com, mgross@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, srinivas.pandruvada@...el.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH 2/2] platform/x86: Add Intel Software Defined Silicon
 driver

On Mon, 2021-09-27 at 06:03 +0200, Greg KH wrote:
> On Sun, Sep 26, 2021 at 06:15:16PM -0700, David E. Box wrote:
> > > > +static int sdsi_remove(struct platform_device *pdev)
> > > > +{
> > > > +       struct sdsi_priv *priv = platform_get_drvdata(pdev);
> > > > +
> > > > +       priv->dev_present = false;
> > > > +       sysfs_remove_bin_file(&priv->pdev->dev.kobj, &priv->registers_bin_attr);
> > > > +       misc_deregister(&priv->miscdev);
> > > > +       kref_put(&priv->kref, sdsi_priv_release);
> > > 
> > > Why do you need a kref for a structure that already can be controlled by
> > > a different lifetime rule?
> > 
> > Which rule am I missing? This kref allows the structure to remain in case the device is removed
> > while the file is open.
> 
> This device is on a hardware bus that allows removal?

Well the device can be unbound. A test case covers this.

> 
> Anyway, you now are dealing with lifetime rules of 3 structures all at
> once, and the interactions between them is not very obvious.  It would
> probably be simpler just to stick with 2, right?  You really only care
> about the misc structure here.

In the case that the device is unbound, both the pdev and miscdev go away. Something has to outlive
them in order to handle any open files still trying to use the ioctl.

David

> 
> thanks,
> 
> greg k-h