RE: [PATCH v11 05/15] platform/x86: dell-wmi-descriptor: split WMI descriptor into it's own driver

[<Mario.Limonciello@dell.com>]

> -----Original Message-----
> From: Pali Rohár [mailto:pali.rohar@gmail.com]
> Sent: Monday, October 30, 2017 6:47 AM
> To: Limonciello, Mario <Mario_Limonciello@Dell.com>
> Cc: dvhart@infradead.org; Andy Shevchenko <andy.shevchenko@gmail.com>;
> LKML <linux-kernel@vger.kernel.org>; platform-driver-x86@vger.kernel.org; Andy
> Lutomirski <luto@kernel.org>; quasisec@google.com; rjw@rjwysocki.net;
> mjg59@google.com; hch@lst.de; Greg KH <greg@kroah.com>; Alan Cox
> <gnomes@lxorguk.ukuu.org.uk>
> Subject: Re: [PATCH v11 05/15] platform/x86: dell-wmi-descriptor: split WMI
> descriptor into it's own driver
> 
> On Friday 20 October 2017 12:40:20 Mario Limonciello wrote:
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.c
> b/drivers/platform/x86/dell-wmi-descriptor.c
> > new file mode 100644
> > index 000000000000..3204c408e261
> > --- /dev/null
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.c
> 
> This dell-wmi-descriptor.c looks good now!
> 
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.h
> b/drivers/platform/x86/dell-wmi-descriptor.h
> > new file mode 100644
> > index 000000000000..5f7b69c2c83a
> > --- /dev/null
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.h
> > @@ -721,7 +652,9 @@ static int dell_wmi_events_set_enabled(bool enable)
> >  static int dell_wmi_probe(struct wmi_device *wdev)
> >  {
> >  	struct dell_wmi_priv *priv;
> > -	int err;
> > +
> > +	if (!wmi_has_guid(DELL_WMI_DESCRIPTOR_GUID))
> > +		return -ENODEV;
> >
> >  	priv = devm_kzalloc(
> >  		&wdev->dev, sizeof(struct dell_wmi_priv), GFP_KERNEL);
> > @@ -729,9 +662,8 @@ static int dell_wmi_probe(struct wmi_device *wdev)
> >  		return -ENOMEM;
> >  	dev_set_drvdata(&wdev->dev, priv);
> >
> > -	err = dell_wmi_check_descriptor_buffer(wdev);
> > -	if (err)
> > -		return err;
> > +	if (!dell_wmi_get_interface_version(&priv->interface_version))
> > +		return -EPROBE_DEFER;
> 
> But here is still a problem. You added check that
> DELL_WMI_DESCRIPTOR_GUID exists in APCI table, but it does not mean that
> probe method of dell-wmi-descriptor cannot fail.
> 
> With PROBE_DEFER, dell_wmi_probe function would be called later again
> and again, even when probing dell-wmi-descriptor failed and so dell-wmi
> in this case cannot work.
> 

Yes it's possible that probe method can fail, but it depends on the reason for
failure if it will fail again later.  For example if not enough memory, it may work
later.  Or maybe user manually unbound from GUID, should continue to try until
it's bound again.

So in short, I believe this is the correct behavior to adopt.