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

["Sören Brinkmann" <soren.brinkmann@xilinx.com>]

On Fri, 2014-08-29 at 05:18PM +0200, Andreas Färber wrote:
> Am 29.08.2014 16:08, schrieb Michal Simek:
> > 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.
> 
> Sorry, but we do need some node that we can reference via phy-handle
> from the gem node, don't we?
> 
> In that case, is not specifying any compatible string a valid option?
> 
> If you don't want to specify the IDs, then I would've assumed we need to
> specify the -c22 in order to have *some* compatible string in order to
> trigger loading of the appropriate driver module.

The compatible string is listed as optional property for PHYs. So, not
having one is an option, I guess. But, I'd also prefer to at least keep
the -c22 one, since I saw problems when I tried using -c45 (the Zed phy
should support it...).
Also, so far, we haven't had any phy nodes in our Zynq dts files and
Ethernet worked, so the auto-detection there works pretty well
apparently. But it may be problematic if more than a single PHY is on
the MDIO bus, I'd assume.

	Sören