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Date:   Thu, 9 Nov 2017 16:13:52 +0000
From:   <Mario.Limonciello@...l.com>
To:     <pali.rohar@...il.com>
CC:     <dvhart@...radead.org>, <andy.shevchenko@...il.com>,
        <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>
Subject: RE: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe
 to dependent drivers

> -----Original Message-----
> From: Pali Rohár [mailto:pali.rohar@...il.com]
> Sent: Thursday, November 9, 2017 10:03 AM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> Cc: dvhart@...radead.org; Andy Shevchenko <andy.shevchenko@...il.com>;
> LKML <linux-kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org
> Subject: Re: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to
> dependent drivers
> 
> On Friday 03 November 2017 11:27:22 Mario Limonciello wrote:
> > dell-wmi and dell-smbios-wmi are dependent upon dell-wmi-descriptor
> > finishing probe successfully to probe themselves.
> >
> > Currently if dell-wmi-descriptor fails probing in a non-recoverable way
> > (such as invalid header) dell-wmi and dell-smbios-wmi will continue to
> > try to redo probing due to deferred probing.
> >
> > To solve this have the dependent drivers query the dell-wmi-descriptor
> > driver whether the descriptor has been determined valid. The possible
> > results are:
> > -EPROBE_DEFER: Descriptor not yet probed, dependent driver should wait
> >  and use deferred probing
> > < 0: Descriptor probed, invalid.  Dependent driver should return an
> >  error.
> > 0: Successful descriptor probe, dependent driver can continue
> >
> > Successful descriptor probe still doesn't mean that the descriptor driver
> > is necessarily bound at the time of initialization of dependent driver.
> > Userspace can unbind the driver, so all methods used from driver
> > should still be verified to return success values otherwise deferred
> > probing be used.
> 
> Darren, Andy, any comments on this patch?
> 
> I think now it should work also those corner, but legit cases.
> 
> > Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> > ---
> >  drivers/platform/x86/dell-smbios-wmi.c     |  4 ++++
> >  drivers/platform/x86/dell-wmi-descriptor.c | 11 +++++++++++
> >  drivers/platform/x86/dell-wmi-descriptor.h |  7 +++++++
> >  drivers/platform/x86/dell-wmi.c            |  5 +++++
> >  4 files changed, 27 insertions(+)
> >
> > diff --git a/drivers/platform/x86/dell-smbios-wmi.c b/drivers/platform/x86/dell-
> smbios-wmi.c
> > index 35c13815b24c..3fa53fa174b2 100644
> > --- a/drivers/platform/x86/dell-smbios-wmi.c
> > +++ b/drivers/platform/x86/dell-smbios-wmi.c
> > @@ -151,6 +151,10 @@ static int dell_smbios_wmi_probe(struct wmi_device
> *wdev)
> >  	if (!wmi_has_guid(DELL_WMI_DESCRIPTOR_GUID))
> >  		return -ENODEV;
> >
> > +	ret = dell_wmi_get_descriptor_valid();
> > +	if (ret)
> > +		return ret;
> > +
> >  	priv = devm_kzalloc(&wdev->dev, sizeof(struct wmi_smbios_priv),
> >  			    GFP_KERNEL);
> >  	if (!priv)
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.c
> b/drivers/platform/x86/dell-wmi-descriptor.c
> > index 28ef5f37cfbf..e7f4c3a7bfc4 100644
> > --- a/drivers/platform/x86/dell-wmi-descriptor.c
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.c
> > @@ -26,9 +26,16 @@ struct descriptor_priv {
> >  	u32 interface_version;
> >  	u32 size;
> >  };
> > +static int descriptor_valid = -EPROBE_DEFER;
> >  static LIST_HEAD(wmi_list);
> >  static DEFINE_MUTEX(list_mutex);
> >
> > +int dell_wmi_get_descriptor_valid(void)
> > +{
> > +	return descriptor_valid;
> > +}
> > +EXPORT_SYMBOL_GPL(dell_wmi_get_descriptor_valid);
> > +
> >  bool dell_wmi_get_interface_version(u32 *version)
> >  {
> >  	struct descriptor_priv *priv;
> > @@ -91,6 +98,7 @@ static int dell_wmi_descriptor_probe(struct wmi_device
> *wdev)
> >  	if (obj->type != ACPI_TYPE_BUFFER) {
> >  		dev_err(&wdev->dev, "Dell descriptor has wrong type\n");
> >  		ret = -EINVAL;
> > +		descriptor_valid = ret;
> >  		goto out;
> >  	}
> >
> > @@ -102,6 +110,7 @@ static int dell_wmi_descriptor_probe(struct wmi_device
> *wdev)
> >  			"Dell descriptor buffer has unexpected length (%d)\n",
> >  			obj->buffer.length);
> >  		ret = -EINVAL;
> > +		descriptor_valid = ret;
> >  		goto out;
> >  	}
> >
> > @@ -111,8 +120,10 @@ static int dell_wmi_descriptor_probe(struct wmi_device
> *wdev)
> >  		dev_err(&wdev->dev, "Dell descriptor buffer has invalid signature
> (%8ph)\n",
> >  			buffer);
> >  		ret = -EINVAL;
> > +		descriptor_valid = ret;
> >  		goto out;
> >  	}
> > +	descriptor_valid = 0;
> >
> >  	if (buffer[2] != 0 && buffer[2] != 1)
> >  		dev_warn(&wdev->dev, "Dell descriptor buffer has unknown
> version (%lu)\n",
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.h
> b/drivers/platform/x86/dell-wmi-descriptor.h
> > index 5f7b69c2c83a..776cddd5e135 100644
> > --- a/drivers/platform/x86/dell-wmi-descriptor.h
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.h
> > @@ -15,6 +15,13 @@
> >
> >  #define DELL_WMI_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-
> B622A1EF5492"
> >
> > +/* possible return values:
> > + *  -EPROBE_DEFER: probing for dell-wmi-descriptor not yet run
> > + *  0: valid descriptor, successfully probed
> > + *  < 0: invalid descriptor, don't probe dependent devices
> > + */
> > +int dell_wmi_get_descriptor_valid(void);
> > +
> >  bool dell_wmi_get_interface_version(u32 *version);
> >  bool dell_wmi_get_size(u32 *size);
> >
> > diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
> > index 54321080a30d..bb7c1e681792 100644
> > --- a/drivers/platform/x86/dell-wmi.c
> > +++ b/drivers/platform/x86/dell-wmi.c
> > @@ -655,10 +655,15 @@ static int dell_wmi_events_set_enabled(bool enable)
> >  static int dell_wmi_probe(struct wmi_device *wdev)
> >  {
> >  	struct dell_wmi_priv *priv;
> > +	int ret;
> >
> >  	if (!wmi_has_guid(DELL_WMI_DESCRIPTOR_GUID))
> >  		return -ENODEV;
> 
> Just one suggestion, is above check still needed in dell-wmi.c code?
> I think that now it should be job of dell_wmi_get_descriptor_valid()
> function to fully validate if dell wmi descriptor driver is able to
> provide all needed information for dell-wmi driver.
> 

Yes, I believe it's still needed because if the GUID isn't on the bus the probe
routine for dell-wmi-descriptor won't run and dell_wmi_get_descriptor_valid()
will continually return -EPROBE_DEFER.

That's the exact problem this patch exists for (preventing infinite deferred
probing).

Perhaps a "cleaner" solution is to have the init routine of dell-wmi-descriptor
do this wmi_has_guid check and set the descriptor_valid variable to -ENODEV 
so that "dependent" drivers don't need to.

> > +	ret = dell_wmi_get_descriptor_valid();
> > +	if (ret)
> > +		return ret;
> > +
> >  	priv = devm_kzalloc(
> >  		&wdev->dev, sizeof(struct dell_wmi_priv), GFP_KERNEL);
> >  	if (!priv)
> 
> --
> Pali Rohár
> pali.rohar@...il.com

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