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

["Pali Rohár" <pali.rohar@gmail.com>]

On Tuesday 31 October 2017 16:31:46 Darren Hart wrote:
> On Mon, Oct 30, 2017 at 01:32:57PM +0000, Mario.Limonciello@dell.com wrote:
> > 
> > 
> > > -----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.
> 
> In this case, I believe the synchronous request_module("dell-wmi-descriptor")
> would provide the desired result. The exit status doesn't even need to be
> checked. If that is successful, and the interface_version still returns false,
> then it can be considered an error and we can exit. If it fails, the
> interface_version will return false, and it is also an error.
> 
> This can be easily added as a single patch on top of this series:
> 
> diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
> index dcfa5de..964ca54 100644
> --- a/drivers/platform/x86/dell-wmi.c
> +++ b/drivers/platform/x86/dell-wmi.c
> @@ -665,8 +665,9 @@ static int dell_wmi_probe(struct wmi_device *wdev)
>  		return -ENOMEM;
>  	dev_set_drvdata(&wdev->dev, priv);
>  
> +	request_module("dell-wmi-descriptor");
>  	if (!dell_wmi_get_interface_version(&priv->interface_version))
> -		return -EPROBE_DEFER;
> +		return -ENODEV;
>  
>  	return dell_wmi_input_setup(wdev);
>  }
> 
> Pali, I believe this addresses your concern?

I'm not sure what happen if both drivers are statically linked into
vmlinuz and dell-wmi probe method would be called before
dell-wmi-descriptor method.

What is doing request_module when requested module is statically linked
into vmlinuz?

-- 
Pali Rohár
pali.rohar@gmail.com