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

From: Joe Hershberger <joe.hershberger@ni.com>
To: u-boot@lists.denx.de
Subject: [U-Boot] [PATCH] net/phy: Fix phy_connect() for phy addr 0
Date: Tue, 17 Dec 2019 18:47:57 +0000	[thread overview]
Message-ID: <CANr=Z=YKkCMDR5M6eM3y8Wxsj3G+_DMMQBUbKHNRnNmUvkUuWg@mail.gmail.com> (raw)
In-Reply-To: <4cecdc1d-cf11-e26f-0bb9-deeeb2bd4d95@denx.de>

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?

> > 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? The code as is should compute a mask of
"0x01" which should match the offset for address 0. If it really is at
0 in hardware, maybe there is a different bug. Otherwise I don't see
how this patch would work for the author.

Thanks,
-Joe