[U-Boot] [PATCH] net/phy: Fix phy_connect() for phy addr 0

[Joe Hershberger <joe.hershberger@ni.com>]

On Tue, Dec 17, 2019 at 11:55 PM Marek Vasut <marex@denx.de> wrote:
>
> On 12/18/19 3:06 AM, Joe Hershberger wrote:
> > On Tue, Dec 17, 2019 at 1:04 PM Marek Vasut <marex@denx.de> wrote:
> >>
> >> On 12/17/19 7:47 PM, Joe Hershberger wrote:
> >>> On Tue, Dec 17, 2019 at 11:46 AM Marek Vasut <marex@denx.de> wrote:
> >>>>
> >>>> On 12/17/19 5:25 PM, Joe Hershberger wrote:
> >>>>> Hi Marek,
> >>>>
> >>>> Hi Joe,
> >>>>
> >>>>> On Tue, Dec 17, 2019 at 1:39 AM Marek Vasut <marex@denx.de> wrote:
> >>>>>>
> >>>>>> On 11/7/19 9:04 PM, Joe Hershberger wrote:
> >>>>>>> On Thu, Nov 7, 2019 at 1:16 PM Tom Rini <trini@konsulko.com> wrote:
> >>>>>>>>
> >>>>>>>> On Tue, Nov 05, 2019 at 04:05:11AM +0000, Priyanka Jain wrote:
> >>>>>>>>
> >>>>>>>>> Fix 'mask' calculation in phy_connect() for phy addr '0'.
> >>>>>>>>> 'mask' is getting set to '0xffffffff' for phy addr '0'
> >>>>>>>>> in phy_connect() whereas expected value is '0'.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>
> >>>>>>>>
> >>>>>>>> Reported-by: tetsu-aoki via github
> >>>>>>>
> >>>>>>> Acked-by: Joe Hershberger <joe.hershberger@ni.com>
> >>>>>>
> >>>>>> Sadly, this breaks systems where a PHY is at address 0.
> >>>>>> I have such an STM32MP1 system with LAN8720 PHY and since this patch, I
> >>>>>> cannot use ethernet. Please revert.
> >>>>>
> >>>>> It seems like a case that shouldn't have worked before.
> >>>>
> >>>> Eh? PHY at address 0 definitely did work before and must work now.
> >>>
> >>> Agreed that a phy at address 0 should work. Not agreed that because
> >>> the value "0" used to work due to a bug that it must still. Which of
> >>> these is the statement you are making? Do we already agree or
> >>> disagree?
> >>
> >> I am saying that because a board worked on rc4 and does not work on rc5,
> >> this is a bug introduced by this patch in rc5 and must be fixed before
> >> the release.
> >>
> >> The address 0 is a PHY broadcast address for some PHYs, it's a fixed
> >> address for other PHYs. Thus, a PHY at address 0 must work. If this is
> >> broken now, it's a bug.
> >
> > The only thing this patch should change is to not access addresses
> > other than 0. I read the data sheet for the LAN8720 and it doesn't
> > mention anything about any broadcast behavior, so I'm not sure what
> > you're trying to state here.
>
> Read [1] section 3.7.1 PHYAD[2:0]: PHY ADDRESS CONFIGURATION
>
> What I am saying is that there are two types of PHYs, ones which treat
> PHY address 0 as broadcast and ones which treat it as regular address.
> This one is the later and is configured as such in my case.
>
> http://ww1.microchip.com/downloads/en/DeviceDoc/00002164B.pdf

I see. What's an example of a phy that treats 0 as broadcast?

> >>>>> What about
> >>>>> this board requires the mask to be all 'f's, other than specifying the
> >>>>> wrong phy address? It seems that in your case the phy address is not
> >>>>> actually 0 (or the computed mask would find it), but your board dts
> >>>>> may be setting it to 0 as an "unknown" value, but the correct unknown
> >>>>> value should be "-1". It seems the issue is with these boards.
> >>>>
> >>>> Nope, the address is actually configured to 0 in hardware.
> >>>
> >>> Can you double check that?
> >>
> >> No, sorry, I know the hardware is fixed to 0. Checking it again will not
> >> change this fact.
> >
> > It seems there is no phy driver for this in U-Boot so the generic
> > behavior is being used. I'm at a disadvantage of not having this board
> > to try. Can you revert this patch and run with debug enabled for
> > drivers/net/phy/phy.c to determine what is happening for this board? I
> > would appreciate you helping with this.
>
> It only says "connected to Generic PHY" .
>
> So looking at the commit message, I am not really sure which board or
> issue does this patch fix. But if I understand the commit message right,
> then the aim is to set mask to 0 instead of 0xffffffff for address 0.
> But that's not right either, the mask should be BIT(0) = 1 for address
> 0, and that's what the patch actually does. I guess this then fails
> somewhere further down the road ...

Yes, the commit message is wrong... the expected value is 1, not 0.  I
missed that in the review.

Is the patch you sent earlier a solution for your board or something
unrelated you found as a result of this discussion?