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    SubjectRE: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to dependent drivers
    Date
    > -----Original Message-----
    > From: platform-driver-x86-owner@vger.kernel.org [mailto:platform-driver-x86-
    > owner@vger.kernel.org] On Behalf Of Pali Rohár
    > Sent: Thursday, November 9, 2017 11:29 AM
    > To: Limonciello, Mario <Mario_Limonciello@Dell.com>
    > Cc: dvhart@infradead.org; andy.shevchenko@gmail.com; linux-
    > kernel@vger.kernel.org; platform-driver-x86@vger.kernel.org
    > Subject: Re: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to
    > dependent drivers
    >
    > On Thursday 09 November 2017 16:13:52 Mario.Limonciello@dell.com wrote:
    > > > -----Original Message-----
    > > > From: Pali Rohár [mailto:pali.rohar@gmail.com]
    > > > Sent: Thursday, November 9, 2017 10:03 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
    > > > 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@dell.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.
    >
    > I understand. But I mean, if function dell_wmi_get_descriptor_valid()
    > should not do that check for DELL_WMI_DESCRIPTOR_GUID itself.
    >
    > Because every driver which would use dell-wmi-descriptor needs to
    > do that check.

    I'll move the check to dell_wmi_descriptor_valid(). That actually does remove
    the need for even including the GUID #define in a header file. All use will be
    contained now directly in dell-wmi-descriptor.c.


    >
    > > > > + 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@gmail.com
    >
    > --
    > Pali Rohár
    > pali.rohar@gmail.com
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