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Date:   Thu, 9 Nov 2017 19:00:45 +0000
From:   <Mario.Limonciello@...l.com>
To:     <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        <dvhart@...radead.org>, <andy.shevchenko@...il.com>
CC:     <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <pali.rohar@...il.com>
Subject: RE: [PATCH v2 2/2] platform/x86: dell-*wmi*: Relay failed initial
 probe to dependent drivers



> -----Original Message-----
> From: platform-driver-x86-owner@...r.kernel.org [mailto:platform-driver-x86-
> owner@...r.kernel.org] On Behalf Of sathyanarayanan kuppuswamy
> Sent: Thursday, November 9, 2017 12:51 PM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>; dvhart@...radead.org;
> Andy Shevchenko <andy.shevchenko@...il.com>
> Cc: LKML <linux-kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org;
> pali.rohar@...il.com
> Subject: Re: [PATCH v2 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to
> dependent drivers
> 
> Hi,
> 
> 
> On 11/09/2017 09:49 AM, Mario Limonciello wrote:
> > dell-wmi and dell-smbios-wmi are dependent upon dell-wmi-descriptor
> > finishing probe successfully to probe themselves.
> if they are dependent, then why not control the device creation of
> dell-wmi and dell-smbios-wmi drivers in del-wmi-descriptor probe ?

The dependency is just in a function call that dell-wmi-descriptor provides
information to the other drivers.

Each of these is a driver that binds to a GUID on the WMI bus.
They can each be built/configured independently of one another and also 
independently bound or unbound to a GUID on the WMI bus. 

Since these are bus drivers, the WMI bus will control creation of devices
when probe routines are run.

> 
> > 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:
> > -ENODEV: Descriptor GUID missing from WMI bus
> > -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.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> > ---
> >   drivers/platform/x86/dell-smbios-wmi.c     |  5 +++--
> >   drivers/platform/x86/dell-wmi-descriptor.c | 16 ++++++++++++++++
> >   drivers/platform/x86/dell-wmi-descriptor.h |  8 +++++++-
> >   drivers/platform/x86/dell-wmi.c            |  6 ++++--
> >   4 files changed, 30 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/platform/x86/dell-smbios-wmi.c b/drivers/platform/x86/dell-
> smbios-wmi.c
> > index 35c13815b24c..ca556803c8c9 100644
> > --- a/drivers/platform/x86/dell-smbios-wmi.c
> > +++ b/drivers/platform/x86/dell-smbios-wmi.c
> > @@ -148,8 +148,9 @@ static int dell_smbios_wmi_probe(struct wmi_device
> *wdev)
> >   	int count;
> >   	int ret;
> >
> > -	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);
> > diff --git a/drivers/platform/x86/dell-wmi-descriptor.c
> b/drivers/platform/x86/dell-wmi-descriptor.c
> > index 28ef5f37cfbf..4dfef1f53481 100644
> > --- a/drivers/platform/x86/dell-wmi-descriptor.c
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.c
> > @@ -21,14 +21,26 @@
> >   #include <linux/wmi.h>
> >   #include "dell-wmi-descriptor.h"
> >
> > +#define DELL_WMI_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-
> B622A1EF5492"
> > +
> >   struct descriptor_priv {
> >   	struct list_head list;
> >   	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)
> > +{
> > +	if (!wmi_has_guid(DELL_WMI_DESCRIPTOR_GUID))
> > +		return -ENODEV;
> > +
> > +	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 +103,7 @@ 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 +115,7 @@ 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 +125,10 @@ 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..1e8cb96ffd78 100644
> > --- a/drivers/platform/x86/dell-wmi-descriptor.h
> > +++ b/drivers/platform/x86/dell-wmi-descriptor.h
> > @@ -13,7 +13,13 @@
> >
> >   #include <linux/wmi.h>
> >
> > -#define DELL_WMI_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-
> B622A1EF5492"
> > +/* possible return values:
> > + *  -ENODEV: Descriptor GUID missing from WMI bus
> > + *  -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..39d2f4518483 100644
> > --- a/drivers/platform/x86/dell-wmi.c
> > +++ b/drivers/platform/x86/dell-wmi.c
> > @@ -655,9 +655,11 @@ 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;
> > +	ret = dell_wmi_get_descriptor_valid();
> > +	if (ret)
> > +		return ret;
> >
> >   	priv = devm_kzalloc(
> >   		&wdev->dev, sizeof(struct dell_wmi_priv), GFP_KERNEL);
> 
> --
> Sathyanarayanan Kuppuswamy
> Linux kernel developer

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