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

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Date:   Fri, 3 Nov 2017 17:53:27 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Mario Limonciello <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 ??


> 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." ??

> 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.

/*
 * 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