Hi,
On Monday 22 July 2013 08:14 PM, Alan Stern wrote:
> On Mon, 22 Jul 2013, Kishon Vijay Abraham I wrote:
>
>>> The PHY and the controller it is attached to are both physical
>>> devices.
>>>
>>> The connection between them is hardwired by the system
>>> manufacturer and cannot be changed by software.
>>>
>>> PHYs are generally described by fixed system-specific board
>>> files or by Device Tree information. Are they ever discovered
>>> dynamically?
>>
>> No. They are created just like any other platform devices are created.
>
> Okay. Are PHYs _always_ platform devices?
Not always. It can be any other device also.
>
>>> Is the same true for the controllers attached to the PHYs?
>>> If not -- if both a PHY and a controller are discovered
>>> dynamically -- how does the kernel know whether they are
>>> connected to each other?
>>
>> No differences here. Both PHY and controller will have dt information or
>> hwmod
>> data using which platform devices will be created.
>>>
>>> The kernel needs to know which controller is attached to which
>>> PHY. Currently this information is represented by name or ID
>>> strings embedded in platform data.
>>
>> right. It's embedded in the platform data of the controller.
>
> It must also be embedded in the PHY's platform data somehow.
> Otherwise, how would the kernel know which PHY to use?
>
>>> The PHY's driver (the supplier) uses the platform data to
>>> construct a platform_device structure that represents the PHY.
>>
>> Currently the driver assigns static labels (corresponding to the label used
>> in
>> the platform data of the controller).
>>> Until this is done, the controller's driver (the client) cannot
>>> use the PHY.
>>
>> right.
>>>
>>> Since there is no parent-child relation between the PHY and the
>>> controller, there is no guarantee that the PHY's driver will be
>>> ready when the controller's driver wants to use it. A deferred
>>> probe may be needed.
>>
>> right.
>>>
>>> The issue (or one of the issues) in this discussion is that
>>> Greg does not like the idea of using names or IDs to associate
>>> PHYs with controllers, because they are too prone to
>>> duplications or other errors. Pointers are more reliable.
>>>
>>> But pointers to what? Since the only data known to be
>>> available to both the PHY driver and controller driver is the
>>> platform data, the obvious answer is a pointer to platform data
>>> (either for the PHY or for the controller, or maybe both).
>>
>> hmm.. it's not going to be simple though as the platform device for the PHY
>> and
>> controller can be created in entirely different places. e.g., in some cases
>> the
>> PHY device is a child of some mfd core device (the device will be created in
>> drivers/mfd) and the controller driver (usually) is created in board file. I
>> guess then we have to come up with something to share a pointer in two
>> different files.
>
> The ability for two different source files to share a pointer to a data
> item defined in a third source file has been around since long before
> the C language was invented. :-)
>
> In this case, it doesn't matter where the platform_device structures
> are created or where the driver source code is. Let's take a simple
> example. Suppose the system design includes a PHY named "foo". Then
> the board file could contain:
>
> struct phy_info { ... } phy_foo;
> EXPORT_SYMBOL_GPL(phy_foo);
>
> and a header file would contain:
>
> extern struct phy_info phy_foo;
>
> The PHY supplier could then call phy_create(&phy_foo), and the PHY
> client could call phy_find(&phy_foo). Or something like that; make up
> your own structure tags and function names.
Alright. Thanks for the hint :-)
Thanks
Kishon
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