[U-Boot] [PATCH V1 1/3] phy: add phy_connect_by_mask

[Eric Nelson]

On 08/22/2012 01:50 PM, Andy Fleming wrote:
> On Wed, Aug 22, 2012 at 3:11 PM, Eric Nelson
> <eric.nelson at boundarydevices.com>  wrote:
>> On 08/20/2012 05:35 PM, Andy Fleming wrote:
>>>
>>> On Monday, August 20, 2012, Troy Kisky wrote:
>>>
>>> It's best if the driver make the reasonable assumption that its PHY
>>> address
>>> is known when it comes up, and let the board code, which can be aware that
>>> the PHY may exist in varying locations, search for the PHY.
>>
>> A mask with a single bit set is about as specific as you can get, right?
>>
>> Are you asking for something more extensible, like a callback into
>> board-specific code?
>
> More like having the board code call into the driver, to tell it:
> Here's where to find your PHY.
>
>>
>>> With that approach, the driver won't have to change when some board
>>> designer makes the PHY topology even stranger, and I would support
>>> a PHYLIB function to do searching much as you've specified.
>>
>> The primary reason for this change is that it's not only the board
>> designer, but also the purchasing manager or manufacturer who can
>> change the address.
>>
>> Since the PHY addresses are often driven by the state of LEDs on
>> an ethernet connector, swapping part numbers can result in different
>> PHY addresses. We run into this on our Nitrogen6X boards where
>> PoE-enabled jacks result in a different PHY address from a standard jack.
>
> Oh, I understand, fully. My argument is actually that it's even worse
> than that. Imagine that there's a scenario where there's a valid PHY
> at 4 AND 6, but under certain circumstances, your controller is hooked
> up to 6. With the mask solution, the driver will always connect to 4
> (assuming your mask includes 4 and 6). So now, to solve that, you have
> to add more logic, but because the knowledge of the PHY is entirely
> encoded in the ethernet driver and the board config file, there's no
> way to insert logic, except in the driver.
>
> I think that many people will find the need to search the bus, and a
> mask like the one in this patch is a very good way. But the driver
> shouldn't do the searching, IMO.
>

Thanks for the clarification Andy. I didn't understand where you were
headed and it's now clear.

Regards,


Eric