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

From: Corentin Labbe <[email-masked]>
Date: Sat, 1 Jul 2017 08:53:58 +0200

On Tue, Jun 27, 2017 at 10:37:34AM -0700, Florian Fainelli wrote:
> On 06/27/2017 10:29 AM, 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 ha>   - it uses an undocumented value, with an unclear implication
> 
> No it's no longer undocumented since [1]
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=29b65f5f97632722bb80969377e5b0e2401fb392
> 
> Due to the timezone difference, you guys have already managed to have
> several exchanges, hopefully I will have a chance to review your
> discussions a little later today.

Hello

I wait for your comment before sending my reverts patch for http://www.mail-archive.com/[email-masked]/msg1431579.html
Could you confirm that internal is only meant for "non xMII internal protocol"

Regards

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