From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Jeremy Linton <jeremy.linton@arm.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net, andrew@lunn.ch,
f.fainelli@gmail.com, hkallweit1@gmail.com,
madalin.bucur@oss.nxp.com, calvin.johnson@oss.nxp.com,
linux-kernel@vger.kernel.org
Subject: Re: [RFC 01/11] net: phy: Don't report success if devices weren't found
Date: Mon, 25 May 2020 10:45:36 +0100 [thread overview]
Message-ID: <20200525094536.GK1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <e6e08ca4-5a6d-5ea3-0f97-946f1d403568@arm.com>
On Sun, May 24, 2020 at 09:46:55PM -0500, Jeremy Linton wrote:
> Hi,
>
> Thanks for taking a look at this.
>
> On 5/23/20 1:20 PM, Russell King - ARM Linux admin wrote:
> > On Fri, May 22, 2020 at 04:30:49PM -0500, Jeremy Linton wrote:
> > > C45 devices are to return 0 for registers they haven't
> > > implemented. This means in theory we can terminate the
> > > device search loop without finding any MMDs. In that
> > > case we want to immediately return indicating that
> > > nothing was found rather than continuing to probe
> > > and falling into the success state at the bottom.
> >
> > This is a little confusing when you read this comment:
> >
> > /* If mostly Fs, there is no device there,
> > * then let's continue to probe more, as some
> > * 10G PHYs have zero Devices In package,
> > * e.g. Cortina CS4315/CS4340 PHY.
> > */
> >
> > Since it appears to be talking about the case of a PHY where *devs will
> > be zero. However, tracking down the original submission, it seems this
> > is not the case at all, and the comment is grossly misleading.
> >
> > It seems these PHYs only report a valid data in the Devices In Package
> > registers for devad=0 - it has nothing to do with a zero Devices In
> > Package.
>
> Yes, this ended up being my understanding of this commit, and is part of my
> justification for starting the devices search at the reserved address 0
> rather than 1.
>
> >
> > Can I suggest that this comment is fixed while we're changing the code
> > to explicitly reject this "zero Devices In package" so that it's not
> > confusing?
>
> Its probably better to kill it in 5/11 with a mention that we are starting
> at a reserved address?
>
> OTOH, I'm a bit concerned that reading at 0 as the first address will cause
> problems because the original code was only triggering it after a read
> returning 0xFFFFFFFF at a valid MMD address. It does simplify/clarify the
> loop though. If it weren't for this 0 read, I would have tried to avoid some
> of the additional MMD reserved addresses.
Yes, that is the worry, and as MMD 0 is marked as reserved, I don't
think we should routinely probe it.
As I've already mentioned, note that bit 0 of devices-in-package does
not mean that there is a MMD 0 implemented, even if bit 0 is set. Bit
0 means that the clause 22 register set is available through clause 22
cycles. So, simplifying the loop to start at 0 and removing the work-
around could end up breaking Cortina PHYs if they don't set bit 0 in
their devices in package - but I don't see why we should depend on bit 0
being set for their workaround.
So, I think you're going to have to add a work-around to ignore bit 0,
which brings up the question whether this is worth it or not.
Hence, I think this is a "simplifcation" too far.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up
next prev parent reply other threads:[~2020-05-25 9:45 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 21:30 [RFC 00/11] Make C45 autoprobe more robust Jeremy Linton
2020-05-22 21:30 ` [RFC 01/11] net: phy: Don't report success if devices weren't found Jeremy Linton
2020-05-23 18:20 ` Russell King - ARM Linux admin
2020-05-25 2:46 ` Jeremy Linton
2020-05-25 9:45 ` Russell King - ARM Linux admin [this message]
2020-05-25 21:02 ` Jeremy Linton
2020-05-25 21:07 ` Russell King - ARM Linux admin
2020-05-25 21:59 ` Jeremy Linton
2020-05-22 21:30 ` [RFC 02/11] net: phy: Simplify MMD device list termination Jeremy Linton
2020-05-23 18:36 ` Russell King - ARM Linux admin
2020-05-25 2:48 ` Jeremy Linton
2020-05-25 8:09 ` Russell King - ARM Linux admin
2020-05-22 21:30 ` [RFC 03/11] net: phy: refactor c45 phy identification sequence Jeremy Linton
2020-05-23 15:28 ` Andrew Lunn
2020-05-23 17:16 ` Jeremy Linton
2020-05-23 17:32 ` Jeremy Linton
2020-05-23 19:12 ` Russell King - ARM Linux admin
2020-05-23 18:30 ` Russell King - ARM Linux admin
2020-05-23 19:51 ` Andrew Lunn
2020-05-23 20:01 ` Russell King - ARM Linux admin
2020-05-25 2:37 ` Jeremy Linton
2020-05-22 21:30 ` [RFC 04/11] net: phy: Handle c22 regs presence better Jeremy Linton
2020-05-23 18:37 ` Russell King - ARM Linux admin
2020-05-25 3:34 ` Jeremy Linton
2020-05-25 9:53 ` Russell King - ARM Linux admin
2020-05-25 10:06 ` Russell King - ARM Linux admin
2020-05-25 21:51 ` Jeremy Linton
2020-05-25 22:01 ` Russell King - ARM Linux admin
2020-05-25 22:22 ` Jeremy Linton
2020-05-25 23:09 ` Russell King - ARM Linux admin
2020-05-25 23:22 ` Jeremy Linton
2020-05-25 23:33 ` Russell King - ARM Linux admin
2020-05-25 23:42 ` Jeremy Linton
2020-05-25 23:46 ` Andrew Lunn
2020-05-25 23:57 ` Russell King - ARM Linux admin
2020-05-25 23:16 ` Jeremy Linton
2020-05-25 23:30 ` Russell King - ARM Linux admin
2020-05-25 22:06 ` Andrew Lunn
2020-05-25 22:17 ` Jeremy Linton
2020-05-25 23:06 ` Andrew Lunn
2020-05-25 23:07 ` Russell King - ARM Linux admin
2020-05-25 23:12 ` Andrew Lunn
2020-05-25 23:46 ` Jeremy Linton
2020-05-25 23:47 ` Andrew Lunn
2020-05-22 21:30 ` [RFC 05/11] net: phy: Scan the entire MMD device space Jeremy Linton
2020-05-22 21:30 ` [RFC 06/11] net: phy: Hoist no phy detected state Jeremy Linton
2020-05-22 21:30 ` [RFC 07/11] net: phy: reset invalid phy reads of 0 back to 0xffffffff Jeremy Linton
2020-05-23 18:44 ` Russell King - ARM Linux admin
2020-05-25 4:20 ` Jeremy Linton
2020-05-25 8:20 ` Russell King - ARM Linux admin
2020-05-22 21:30 ` [RFC 08/11] net: phy: Allow mdio buses to auto-probe c45 devices Jeremy Linton
2020-05-24 14:44 ` Andrew Lunn
2020-05-25 4:28 ` Jeremy Linton
2020-05-25 8:25 ` Russell King - ARM Linux admin
2020-05-25 13:43 ` Andrew Lunn
2020-05-25 22:09 ` Jeremy Linton
2020-05-25 22:41 ` Russell King - ARM Linux admin
2020-05-22 21:30 ` [RFC 09/11] net: phy: Refuse to consider phy_id=0 a valid phy Jeremy Linton
2020-05-22 21:30 ` [RFC 10/11] net: example acpize xgmac_mdio Jeremy Linton
2020-05-23 18:48 ` Russell King - ARM Linux admin
2020-05-22 21:30 ` [RFC 11/11] net: example xgmac enable extended scanning Jeremy Linton
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