Subject: Re: [PATCH v6 05/21] net-next: stmmac: Add dwmac-sun8i

From: Corentin Labbe <[email-masked]>
Date: Tue, 27 Jun 2017 19:37:27 +0200

On Tue, Jun 27, 2017 at 07:29:37PM +0200, Maxime Ripard wrote:
> On Tue, Jun 27, 2017 at 02:37:48PM +0200, Corentin Labbe wrote:
> > On Tue, Jun 27, 2017 at 11:33:56AM +0100, Andre Przywara wrote:
> > > Hi,
> > > 
> > > On 27/06/17 11:23, Icenowy Zheng wrote:
> > > > 
> > > > 
> > > > 于 2017年6月27日 GMT+08:00 下午6:15:58, Andre Przywara <[email-masked]> 写到:
> > > >> Hi,
> > > >>
> > > >> On 27/06/17 10:41, Maxime Ripard wrote:
> > > >>> On Tue, Jun 27, 2017 at 10:02:45AM +0100, Andre Przywara wrote:
> > > >>>> Hi,
> > > >>>>
> > > >>>> (CC:ing some people from that Rockchip dmwac series)
> > > >>>>
> > > >>>> On 27/06/17 09:21, Corentin Labbe wrote:
> > > >>>>> On Tue, Jun 27, 2017 at 04:11:21PM +0800, Chen-Yu Tsai wrote:
> > > >>>>>> On Tue, Jun 27, 2017 at 4:05 PM, Corentin Labbe
> > > >>>>>> <[email-masked]> wrote:
> > > >>>>>>> On Mon, Jun 26, 2017 at 01:18:23AM +0100, André Przywara wrote:
> > > >>>>>>>> On 31/05/17 08:18, Corentin Labbe wrote:
> > > >>>>>>>>> The dwmac-sun8i is a heavy hacked version of stmmac hardware by
> > > >>>>>>>>> allwinner.
> > > >>>>>>>>> In fact the only common part is the descriptor management and
> > > >> the first
> > > >>>>>>>>> register function.
> > > >>>>>>>>
> > > >>>>>>>> Hi,
> > > >>>>>>>>
> > > >>>>>>>> I know I am a bit late with this, but while adapting the U-Boot
> > > >> driver
> > > >>>>>>>> to the new binding I was wondering about the internal PHY
> > > >> detection:
> > > >>>>>>>>
> > > >>>>>>>>
> > > >>>>>>>> So here you seem to deduce the usage of the internal PHY by the
> > > >> PHY
> > > >>>>>>>> interface specified in the DT (MII = internal, RGMII =
> > > >> external).
> > > >>>>>>>> I think I raised this question before, but isn't it perfectly
> > > >> legal for
> > > >>>>>>>> a board to use MII with an external PHY even on those SoCs that
> > > >> feature
> > > >>>>>>>> an internal PHY?
> > > >>>>>>>> On the first glance that does not make too much sense, but apart
> > > >> from
> > > >>>>>>>> not being the correct binding to describe all of the SoCs
> > > >> features I see
> > > >>>>>>>> two scenarios:
> > > >>>>>>>> 1) A board vendor might choose to not use the internal PHY
> > > >> because it
> > > >>>>>>>> has bugs, lacks features (configurability) or has other issues.
> > > >> For
> > > >>>>>>>> instance I have heard reports that the internal PHY makes the
> > > >> SoC go
> > > >>>>>>>> rather hot, possibly limiting the CPU frequency. By using an
> > > >> external
> > > >>>>>>>> MII PHY (which are still cheaper than RGMII PHYs) this can be
> > > >> avoided.
> > > >>>>>>>> 2) A PHY does not necessarily need to be directly connected to
> > > >>>>>>>> magnetics. Indeed quite some boards use (RG)MII to connect to a
> > > >> switch
> > > >>>>>>>> IC or some other network circuitry, for instance fibre
> > > >> connectors.
> > > >>>>>>>>
> > > >>>>>>>> So I was wondering if we would need an explicit:
> > > >>>>>>>>       allwinner,use-internal-phy;
> > > >>>>>>>> boolean DT property to signal the usage of the internal PHY?
> > > >>>>>>>> Alternatively we could go with the negative version:
> > > >>>>>>>>       allwinner,disable-internal-phy;
> > > >>>>>>>>
> > > >>>>>>>> Or what about introducing a new "allwinner,internal-mii-phy"
> > > >> compatible
> > > >>>>>>>> string for the *PHY* node and use that?
> > > >>>>>>>>
> > > >>>>>>>> I just want to avoid that we introduce a binding that causes us
> > > >>>>>>>> headaches later. I think we can still fix this with a followup
> > > >> patch
> > > >>>>>>>> before the driver and its binding hit a release kernel.
> > > >>>>>>>>
> > > >>>>>>>> Cheers,
> > > >>>>>>>> Andre.
> > > >>>>>>>>
> > > >>>>>>>
> > > >>>>>>> I just see some patch, where "phy-mode = internal" is valid.
> > > >>>>>>> I will try to find a way to use it
> > > >>>>>>
> > > >>>>>> Can you provide a link?
> > > >>>>>
> > > >>>>> https://lkml.org/lkml/2017/6/23/479
> > > >>>>>
> > > >>>>>>
> > > >>>>>> I'm not a fan of using phy-mode for this. There's no guarantee
> > > >> what
> > > >>>>>> mode the internal PHY uses. That's what phy-mode is for.
> > > >>>>
> > > >>>> I can understand Chen-Yu's concerns, but ...
> > > >>>>
> > > >>>>> For each soc the internal PHY mode is know and setted in
> > > >> emac_variant/internal_phy
> > > >>>>> So its not a problem.
> > > >>>>
> > > >>>> that is true as well, at least for now.
> > > >>>>
> > > >>>> So while I agree that having a separate property to indicate
> > > >>>> the usage of the internal PHY would be nice, I am bit tempted
> > > >>>> to use this easier approach and piggy back on the existing
> > > >>>> phy-mode property.
> > > >>>
> > > >>> We're trying to fix an issue that works for now too.
> > > >>>
> > > >>> If we want to consider future weird cases, then we must
> > > >>> consider all of them. And the phy mode changing is definitely
> > > >>> not really far fetched.
> > > >>>
> > > >>> I agree with Chen-Yu, and I really feel like the compatible
> > > >>> solution you suggested would cover both your concerns, and
> > > >>> ours.
> > > >>
> > > >> So something like this?
> > > >> 	emac: emac@1c30000 {
> > > >> 	    compatible = "allwinner,sun8i-h3-emac";
> > > >> 	    ...
> > > >> 	    phy-mode = "mii";
> > > >> 	    phy-handle = <&int_mii_phy>;
> > > >> 	    ...
> > > >>
> > > >> 	    mdio: mdio {
> > > >>                #address-cells = <1>;
> > > >>                #size-cells = <0>;
> > > >>                int_mii_phy: ethernet-phy@1 {
> > > >>                    compatible = "allwinner,sun8i-h3-ephy";
> > > >>                    syscon = <&syscon>;
> > > > 
> > > > The MAC still needs to set some bits of syscon register.
> > > 
> > > Yes, the syscon property needs also to be in the MAC node, that
> > > was meant to be somewhere in the second "..." ;-)
> > > 
> > > But now since Chen-Yu mentioned that we need to set up the PHY *first*
> > > to make it actually discoverable via MDIO, I wonder if we could change
> > > this to:
> > > 1) have the DT as described here
> > > 2) Let the dwmac-sun8i driver peek into the node referenced by
> > > phy-handle and check the compatible string there.
> > > 3) If that matches some allwinner internal PHY name, it sets up the PHY
> > > to make it respond when the MDIO driver queries its bus.
> > > 
> > > Or can a PHY driver set itself up (since we have clocks and resets
> > > properties in there) *before* the MDIO bus gets scanned?
> > > Chen-Yu's comment in the other mail hints at that this is not easily
> > > possible.
> > 
> > I think adding phy compatible just make things more complex.
> > 
> > I think the patch series I sent early fix all problems without more
> > complexity since:
> >
> > - it does not add more DT stuff
> > - it use an already used in tree DT phy-mode "internal" (and so phy
> >   mode PHY_INTERFACE_MODE_INTERNAL)
> 
>   - it doesn't cover all the concerns we had
>   - it uses an undocumented value, with an unclear implication
> 

The answer from Florian anyway breaks my logic, internal is for "internal phy with non-xMII protocol" not just internal PHY

Regards

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