Re: [PATCH 3/3] ARM: zynq: DT: Add Ethernet phys

From: Michal Simek
Date: Fri Aug 29 2014 - 10:26:03 EST

On 08/25/2014 10:21 PM, Florian Fainelli wrote:
> On 08/25/2014 10:46 AM, Jason Gunthorpe wrote:
>> On Fri, Aug 22, 2014 at 01:47:09PM -0700, Florian Fainelli wrote:
>>>> - the ID based strings seem to be not needed since, IIUC, the core
>>>> reads the ID from the PHY and uses it, so I just left it out not
>>>> trying to figure out how to obtain the correct ID
>>> It is not needed, but it is one way to specify a PHY device if you do
>>> not know what compatible string to use instead.
>> No, it is a way to specify a PHY device if the kernel can't auto probe
>> the Phy ID.
>> Last I checked, the kernel doesn't support plain text compatible
>> strings for phys - everything is driven on the phy id, either auto
>> probed or specified in the DT.
> That's right. Some PHY drivers might be relying on specific compatible
> strings though, but not the core PHY library that probes and maps a
> driver to a PHY node.
>>>> - the marvell compatible strings are used in our vendor tree. They
>>>> aren't used anywhere but in our vendor tree. I though keeping them is
>>>> nice since it identifies the PHY fully. And in case that level of
>>>> detail is needed at some point it is already there.
>>> And this is the recommended way to do it in case we ever need to key a
>>> software decision based on the hardware.
>> All compatible strings need to be documented.
>> .. and they need to encode more information than you get from the phy
>> id - die revsision, package option, functional options, voltage
>> codes. Etc.
>> .. and they actually need to be *right*
> Agreed.
>> An example: The kernel reports 88E1318S for all four chips in that
>> family, AFAIK you have to read the package marking to figure out which
>> you have (it is the same die, with options switched on/off at
>> packaging time). People have already posted patches trying to
>> helpfully add a 'marvell,88E1318S' compatible string based on kernel
>> output. Except it is wrong, it isn't actually the '8S version in the
>> HW.
>> Even worse, Marvell has a whole series of socket compatible phys. Just
>> because the board the DT author looked at has a '318, doesn't mean
>> that every board ever made will. We've actually already been switching
>> between the 318 and 318S for production depending on which has part
>> availability.
>> Basically: don't try to override self-discoverable hardware in DT
>> without a really good reason.
> I think that's a very good point, at the very least let's use a
> compatible string that contains the full 32-bits PHY OUI.

I think resolution is:
1. Do not use marvell,88e1518 because it is not listed anywhere
2. Do not add ethernet-phy-idAAAA.BBBB because it breaks autodetection
if there is different phy on the board and we shouldn't restrict us in this.
In spite of autodetection takes some time.
3. "ethernet-phy-ieee802.3-c22" is optional that's why doesn't need to be added
4. Any listed compatible string has to be parsed which takes time

That's why I think make sense not to use any compatible string.
This should give us all flexibility which we want to have.


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