linux-kernel - RE: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to dependent drivers

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Date:   Sat, 4 Nov 2017 03:25:04 +0000
From:   <Mario.Limonciello@...l.com>
To:     <dvhart@...radead.org>
CC:     <andy.shevchenko@...il.com>, <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <pali.rohar@...il.com>
Subject: RE: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe
 to dependent drivers

> -----Original Message-----
> From: Darren Hart [mailto:dvhart@...radead.org]
> Sent: Friday, November 3, 2017 7:53 PM
> To: Limonciello, Mario <Mario_Limonciello@...l.com>
> Cc: Andy Shevchenko <andy.shevchenko@...il.com>; LKML <linux-
> kernel@...r.kernel.org>; platform-driver-x86@...r.kernel.org;
> pali.rohar@...il.com
> Subject: Re: [PATCH 2/2] platform/x86: dell-*wmi*: Relay failed initial probe to
> dependent drivers
> 
> On Fri, Nov 03, 2017 at 11:27:22AM -0500, 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
> 
> Userspace shouldn't be able to remove the dell-wmi-descriptor driver if a
> dependent driver is loaded. It isn't clear to me in which scenario we encounter
> this problem ??

Userspace can however unbind a bound GUID.  When this happens getting
the interface version and size will both fail.

> 
> 
> > should still be verified to return success values otherwise deferred
> > probing be used.
> 
> The part after "otherwise" is breaking my English parser...
> 
> Should this read: "Userspace can unbind the driver, so all methods used from the
> driver should still be verified to return successful values, falling back to
> deferred probing in case of failure." ??

Yeah that's clearer and correct.

> 
> > 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:
> 
> This should trigger a checkpatch error, but doesn't. Huh. For everything but
> "net", comment blocks should start with /* and not following text.
> 

OK.

> /*
>  * First line.
>  * Second line.
>  */
> 
> A nit, and I can clean up if no changes are deemed necessary here.
> 
> > + *  -EPROBE_DEFER: probing for dell-wmi-descriptor not yet run
> > + *  0: valid descriptor, successfully probed
> > + *  < 0: invalid descriptor, don't probe dependent devices
> > + */
> 
> --
> Darren Hart
> VMware Open Source Technology Center