linux-kernel - Re: [PATCH 1/3] Documentation/auxiliary_bus: Clarify auxiliary

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Message-ID: <87k0hq2oxc.fsf@meer.lwn.net>
Date:   Tue, 02 Nov 2021 16:06:07 -0600
From:   Jonathan Corbet <corbet@....net>
To:     ira.weiny@...el.com
Cc:     Ira Weiny <ira.weiny@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/3] Documentation/auxiliary_bus: Clarify
 auxiliary_device creation

ira.weiny@...el.com writes:

> From: Ira Weiny <ira.weiny@...el.com>
>
> The documentation for creating an auxiliary device is a 3 step not a 2
> step process.  Specifically the requirements of setting the name, id,
> dev.release, and dev.parent fields was not clear as a precursor to the '2
> step' process documented.
>
> Clarify by declaring this a 3 step process starting with setting the
> fields of struct auxiliary_device correctly.
>
> Also add some sample code and tie the change into the rest of the
> documentation.
>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Looks generally good but ...

>  Documentation/driver-api/auxiliary_bus.rst | 77 +++++++++++++++++-----
>  1 file changed, 59 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/driver-api/auxiliary_bus.rst b/Documentation/driver-api/auxiliary_bus.rst
> index ef902daf0d68..8b3e795f3691 100644
> --- a/Documentation/driver-api/auxiliary_bus.rst
> +++ b/Documentation/driver-api/auxiliary_bus.rst
> @@ -79,18 +79,6 @@ is given a name that, combined with the registering drivers KBUILD_MODNAME,
>  creates a match_name that is used for driver binding, and an id that combined
>  with the match_name provide a unique name to register with the bus subsystem.
>  
> -Registering an auxiliary_device is a two-step process.  First call
> -auxiliary_device_init(), which checks several aspects of the auxiliary_device
> -struct and performs a device_initialize().  After this step completes, any
> -error state must have a call to auxiliary_device_uninit() in its resolution path.
> -The second step in registering an auxiliary_device is to perform a call to
> -auxiliary_device_add(), which sets the name of the device and add the device to
> -the bus.
> -
> -Unregistering an auxiliary_device is also a two-step process to mirror the
> -register process.  First call auxiliary_device_delete(), then call
> -auxiliary_device_uninit().
> -
>  .. code-block:: c
>  
>  	struct auxiliary_device {
> @@ -99,15 +87,68 @@ auxiliary_device_uninit().
>  		u32 id;
>  	};
>  
> -If two auxiliary_devices both with a match_name "mod.foo" are registered onto
> -the bus, they must have unique id values (e.g. "x" and "y") so that the
> -registered devices names are "mod.foo.x" and "mod.foo.y".  If match_name + id
> -are not unique, then the device_add fails and generates an error message.
> +Registering an auxiliary_device is a three-step process.
> +
> +First, a 'struct auxiliary_device' needs to be defined or allocated for each
> +sub-device desired.  The name, id, dev.release, and dev.parent fields of this
> +structure must be filled in as follows.
> +
> +The 'name' field is to be given a name that is recognized by the auxiliary
> +driver.  If two auxiliary_devices with the same match_name, eg
> +"mod.MY_DEVICE_NAME", are registered onto the bus, they must have unique id
> +values (e.g. "x" and "y") so that the registered devices names are "mod.foo.x"
> +and "mod.foo.y".  If match_name + id are not unique, then the device_add fails
> +and generates an error message.
>  
>  The auxiliary_device.dev.type.release or auxiliary_device.dev.release must be
> -populated with a non-NULL pointer to successfully register the auxiliary_device.
> +populated with a non-NULL pointer to successfully register the
> +auxiliary_device.  This release call is where resources associated with the
> +auxiliary device must be free'ed.  Because once the device is placed on the bus
> +the parent driver can not tell what other code may have a reference to this
> +data.
> +
> +The auxiliary_device.dev.parent should be set.  Typically to the registering
> +drivers device.
> +
> +Second, call auxiliary_device_init(), which checks several aspects of the
> +auxiliary_device struct and performs a device_initialize().  After this step
> +completes, any error state must have a call to auxiliary_device_uninit() in its
> +resolution path.
> +
> +The third and final step in registering an auxiliary_device is to perform a
> +call to auxiliary_device_add(), which sets the name of the device and adds the
> +device to the bus.
> +
> +.. code-block:: c
> +
> +	struct axiliary_device *my_aux_dev = my_aux_dev_alloc(xxx);

This ----------^  would appear to be a typo...

Thanks,

jon